EEVblog® Electronics Community Forum
Products => Test Equipment => Topic started by: KungFuJosh on May 31, 2025, 03:22:00 pm
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They have some nice cables that are also ~$30. We don't have any (yet?), but will probably order some next time we order from them (or Mouser).
I may try one at some point for comparison, but I just blew a bunch of money on the M&P stuff, which I'm happy with anyway.
Having them custom make me that Stealthflex 7 cable was about $34 after conversion, so not bad at all really. That price included the fee for the attached report I was also curious about.
Thanks,
Josh
You should do a test of the cable to compare with OEM Data sheet. Nice they provide the measurement and for a custom quality cable with N and BNC type connectors at that price!! The M&P cables/connectors look like a very good value and quality product.
Since these newer DSOs are venturing into the upper UHF region, maybe start a thread on cables, connectors (N/SMA/BNC) & Adapters with measured results for comparisons. Most DSOs utilize BNC inputs, so info should emphasize at least 1 BNC connector/adapter/cable type.
This might prove useful for folks and save some $ as we've all been down the cheap cable/connector route, ourselves more times than we care to admit :-\
We need to set some standard testing parameters that people can do with scopes. I don't have a VNA yet to test cables.
Maybe we should set some test parameters for different devices.
Thanks,
Josh
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...a high quality inline attenuator of at least 6 dB (more is better) directly at the generator output.
How's this?: https://www.pasternack.com/12db-fixed-n-male-n-female-2-watts-attenuator-pe7047-12-p.aspx (https://www.pasternack.com/12db-fixed-n-male-n-female-2-watts-attenuator-pe7047-12-p.aspx)
This one looks very good. It will allow you to explot the full bandwidth of your generator.
I assume this is not good enough: https://www.amazon.com/dp/B0DKFDD3KT/ (https://www.amazon.com/dp/B0DKFDD3KT/)
It doesn't look that bad, but with a rated bandwidth of 3 GHz, it might not perform optimally at frequencies above 1 GHz. On the other hand, cables have a frequency dependant attenuation also, hence this concern might not apply.
With regard to the cable, the Hyperflex 5 is about the best with ~5 mm diameter we can get up to 2 GHz. You would have a hard time finding a better one, regardless the price.
Above 2 GHz, there might be better options, although vastly more expensive.
M&P's datasheet seems to be pretty good. It even suggest using thicker cables for specific situations.
In my case, at least for the moment, I won't be going above 1 or 2GHz, so I hope I can get away with the 6GHz max attenuator Mike suggested, the UNAT-10A+ (datasheet attached). It was only ~$30 on Mouser. A few dollars cheaper on DigiKey.
Thanks,
Josh
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If you don't have the money for a real VNA, just use a nanovna or litevna. Pretty sure you would get better result than trying to macgyver something with a scope and siggen. At least it's going to be simpler.
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^^^ Agree :-+
@ Josh
Get one of those inexpensive VNAs, this can serve as a "Reference" for the cable DUT. Then the DSO results will have a good comparison to work with, if the cable, like your M&P, comes with a measured data sheet all the better!!
Anyway, thanks for creating this thread, think it will be very useful of many folks!!
Best
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Fine, fine. I'll buy a VNA. I'm planning to anyway, I'm just waiting for a good deal. I probably won't buy a TinyVNA. I have a TinySA Ultra, and it still makes me want a real SA or VNA.
We still need parameters for test setups. I don't know how to setup a cable test on a VNA, considering I've never used a VNA. ;)
Thanks,
Josh
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At the time, I was advised to buy an inexpensive Nano VNA first before embarking on the adventure of a “real” VNA.
I am still grateful for this advice today, because I recently sold my Nano VNA—it was all too fiddly for me, and then there was always the calibration before every use.
(Well, I could now convert my new SSA3021Xplus into a 3.2 GHz VNA, but I still need to think about that very carefully).
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My experience with the TinySA Ultra was similar. All it did was convince me I need a full size / more powerful SA. I think I'll skip that step this time. ;)
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At the time, I was advised to buy an inexpensive Nano VNA first before embarking on the adventure of a “real” VNA.
I am still grateful for this advice today, because I recently sold my Nano VNA—it was all too fiddly for me, and then there was always the calibration before every use.
(Well, I could now convert my new SSA3021Xplus into a 3.2 GHz VNA, but I still need to think about that very carefully).
Hello,
Calibration is also necessary for expensive VNAs. However, there are certain automatic devices available.
There are good PC programs for the NanoVNA, which make it convenient to use.
But VNAs are great.
The PicoVNA manual is good, as it can also be applied to other VNAs.
Best regards
egonotto
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Which version of the NanoVNA is good? I might get one to screw with until I find a decent deal on a "real" VNA.
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LiteVNA
https://video.search.yahoo.com/search/video?fr=mcafee&p=lite+vna+joe+smith&type=E210US105G91906#id=2&vid=21b38ba6f56bd4d68b3de47b72ec2abf&action=click
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The one I had is supposed to be good.
I asked myself the same question last year, Josh:
https://www.eevblog.com/forum/testgear/nano-vna-like-sand-on-the-sea-who-is-the-good-one/msg5567911/#msg5567911 (https://www.eevblog.com/forum/testgear/nano-vna-like-sand-on-the-sea-who-is-the-good-one/msg5567911/#msg5567911)
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Which version of the NanoVNA is good? I might get one to screw with until I find a decent deal on a "real" VNA.
NanoVNA is good at low freq, LiteVNA at higher freq. I bought from Zeenko store in the past and they are reliable (https://zeenko.ja.aliexpress.com/store/1101394653 (https://zeenko.ja.aliexpress.com/store/1101394653)).
The screen size and battery might not matter if you are planning to use it connected to a computer.
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I am still grateful for this advice today, because I recently sold my Nano VNA—it was all too fiddly for me, and then there was always the calibration before every use.
You can save calibration on the device or PC if using a external software.
I normally use it via a computer and have bunch of calibration saved for different setups.
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Would I be better off with the LibreVNA if I'm going to use it on a computer anyway?
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You know you can save calibration right ?
Too late... ;)
But thanks anyway.
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Would I be better off with the LibreVNA if I'm going to use it on a computer anyway?
I personally have no experience with the LIbreVNA, but the electronic calibration kit for it is interesting https://www.aliexpress.com/item/1005008002497171.html (https://www.aliexpress.com/item/1005008002497171.html)
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Would I be better off with the LibreVNA if I'm going to use it on a computer anyway?
I personally have no experience with the LIbreVNA, but the electronic calibration kit for it is interesting https://www.aliexpress.com/item/1005008002497171.html (https://www.aliexpress.com/item/1005008002497171.html)
Apparently it can be used to calibrate other VNAs too. A user on this site used it on a Siglent VNA.
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Would I be better off with the LibreVNA if I'm going to use it on a computer anyway?
I personally have no experience with the LIbreVNA, but the electronic calibration kit for it is interesting https://www.aliexpress.com/item/1005008002497171.html (https://www.aliexpress.com/item/1005008002497171.html)
Also look like the LibreVNA is a full 2 ports device (can measure all S parameters) and the other cheap VNA are not (only S11, S21).
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There's also the NanoVNA SV4401A. That looks interesting too. 7" screen with 2 N ports.
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NanoVNA is good at low freq, LiteVNA at higher freq.
Why? What makes one better than the other?
LiteVNA-64 max is 6GHz, and NanoVNA-F V3 is also maxed at 6GHz. Is there something else that makes one better than the other in your opinion?
I'm leaning towards the NanoVNA-F V2 that Martin had, since 3GHz is probably good enough for me, and the price is better.
More importantly- can these devices be used for the purpose of this thread- to accurate test cables?
Thanks,
Josh
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NanoVNA is good at low freq, LiteVNA at higher freq.
Why? What makes one better than the other?
LiteVNA-64 max is 6GHz, and NanoVNA-F V3 is also maxed at 6GHz. Is there something else that makes one better than the other in your opinion?
I'm leaning towards the NanoVNA-F V2 that Martin had, since 3GHz is probably good enough for me, and the price is better.
More importantly- can these devices be used for the purpose of this thread- to accurate test cables?
Thanks,
Josh
Maybe 9G with harmonics.
We need to set some standard testing parameters that people can do with scopes. I don't have a VNA yet to test cables.
You mention testing them with a scope so I am assuming you are referring to typical patch cables for low frequency use around the home lab. I would just eye ball the connectors for damage, clean them and check if flexing them causes any problems.
Obviously all cables are not the same. Higher grade cables like you may use with a VNA could costs thousands of USD each! They can be easily damaged.
Someone was recently shitting on various brands for making cables that did not meet spec. I made an attempt to measure a few and provide further details.
https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/ (https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/)
The very last post I made was using the LiteVNA to measure insertion loss of a Mini-Circuits cable. That particular cable is spec'ed out to 18GHz which is outside what could be measured with the LiteVNA.
https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5923980/#msg5923980 (https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5923980/#msg5923980)
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... since 3GHz is probably good enough for me ...
The following link shows using a T-check with the LiteVNA. This is just a simple method to verify your setup after calibration. After attempts to remove as many variables as possible, I was able to squeeze decent performance to 3GHz with it.
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5685217/#msg5685217 (https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5685217/#msg5685217)
Showing the dynamic range of the three hardware revisions of the LiteVNA to 9GHz. Consider you would normally want about 10dB margin. Still, for very rough measurements, it could be useful.
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/2450/ (https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/2450/)
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NanoVNA is good at low freq, LiteVNA at higher freq.
Why? What makes one better than the other?
I remember reading/listing joeqsmith experiments with the litevna and he was mentioning the original nanovna was performing better at lower freq. Maybe joe could elaborate more.
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I'll have the NanoVNA-F V2 tomorrow. Now I just need to learn how to use a VNA. 🤷
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From a black box view point, the original NanoVNA had lower noise and could be used for narrow band measurements (crystal filters) which the LiteVNA, V2+ can't. The cost was less than half.
We bought two H4s which are similar to the original NanoVNA with a 4" display. These never performed as well as the original NanoVNAs we bought. I ended up damaging my H4 and while trying to repair it stumbled onto that the mixers they used in the original NanoVNA induced less noise. I ended up adding a few caps and changing the mixers on the H4 and it out performed the original NanoVNA. I ended up making the same mods to my friend's H4 and the performance was on-par with mine. Maybe the early H4's were better. I posted about it here:
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5695997/#msg5695997 (https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5695997/#msg5695997)
The H4 and NanoVNA are only good for about 300MHz. They support harmonics but the dynamic range is poor. So, < 300MHz, narrow band, PDN sort of measurements, NanoVNA. Greater than 300, LiteVNA. They are low cost, so if you play with RF, get them both and you're set.
Just don't be fooled into thinking they are going to compete with a name brand VNA. They are slower, missing key features and use a square wave. People will post how the square wave doesn't matter. I agree in most applications that is true. Certainly for passive devices. However, if you are playing with active circuits that may not be the case, even when working with very low frequencies. Here I demonstrate a 1MHz amplifier that I purposely designed to show how the square wave can be problematic.
https://www.youtube.com/watch?v=y6iOTEU6Zzo (https://www.youtube.com/watch?v=y6iOTEU6Zzo)
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@Josh:
I'm currently on chapter 4...
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I'll have the NanoVNA-F V2 tomorrow. Now I just need to learn how to use a VNA. 🤷
Looks similar to my V2+4. The LiteVNA quickly obsoleted it. The Lite provided a wider sweep range, input protection and the biggest advantage, Dislord!! After dealing with so much crap firmware, it was refreshing to see how polished the the Lite was. I only use these with a PC, so I really could care less about 90% of the features added to the firmware. But the Lite has features that the V2+4 will never have because of the closed architecture.
Cost wise, I suspect you could buy the Lite + original Nano for the same amount as the V2+4.
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I bought the NanoVNA-F V2 for $125. The LiteVNA-64 is $160. It's a small price difference if you think it's that much better.
These seem like toys to learn on. Is the LibreVNA a more serious device, or is it just a more expensive toy?
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I bought the NanoVNA-F V2 for $125. The LiteVNA-64 is $160. It's a small price difference if you think it's that much better.
These seem like toys to learn on. Is the LibreVNA a more serious device, or is it just a more expensive toy?
I have used mine for professional work. I wouldn't call them toys. When you do something stupid, you're not out much $$$. We had to replace a 3.5mm short standard a while back. $1000 USD. My guess is someone allowed the center pin to rotate in it. That's all it takes. The LiteVNA has some input protection but my NanoVNA and H4 did not. I have no idea how I damaged my H4 as I normally work on an ESD mat and wear a strap but something blew out the front end. I ended up doing the repairs and adding a TVS to both ports. This isn't something I would ever consider with an expensive VNA.
Like buying anything else, I would have no way to know what metrics are important to you. I run them from a PC. Things like a large LCD (which is turned off when connected to USB), card readers, built in measurements, battery life, are not something I care about. Even the mechanical robustness is not a concern. Like the handheld DMMs, I don't own a VNA that would fit all my needs. Like the DMMs, these low cost VNAs are good enough that they cover a lot of my needs. I often use them over my old Agilent/HP equipment!
Overall, if you wanted to compare what you have with my LiteVNA + NanoVNA combo, sure, you would win on a cost basis but for me even $100 cost savings wouldn't be something I would consider over the performance. Specs for the three are below. I'm not sure I would trust them though. For example, they may claim a 100dB dynamic range but fail to tell you it requires an hour to do a sweep. Beware. I try to provide details about any measurements I post about.
I saw they now have an e-cal for the LibreVNA, and I understand they can do a full 2-port measurement with it. But I started seeing everyone sticking massive heat sinks to them. As soon as it was released, the designer was talking about the next generation (couldn't see buying a second one down). The software interface was locked (eventually opened up) but the developer warned me that it could very well change. Then the performance just wasn't there. With the ecal, say $700ish, we are not really talking disposable for many hobbyist.
I think they all have a bit of a fan following. Many seem to be hams wanting to measure their antenna VSWR in the most complex manner possible and will refer to them as an antenna analyzer. Because I write my own software, I have shown using the VNA being used to measure radiation patterns (in 3D). All automatically. Being able to write custom software for any test equipment is a must have. My choice on the low cost VNAs were based on performing tasks far beyond measuring antennas.
Sysjoint NanoVNA-F V2
Measuring frequency: 50kHz~3000MHz
RF output power: - 9dbm
S11 dynamic range: 50dB(<1.5GHz), 40dB(<3GHz)
S21 dynamic range: 70dB(<1.5GHz), 60dB(<3GHz)
Frequency tolerance: <0.5ppm
Port SWR: <1.1
Display: 4.3" IPS TFT(800x480)
Output capability: 5V/1A
USB interface: USB Type-C
Power consumption: 3.7V Li-Po, 5000mAh
Number of scan points: 101
Display trace: Up to 4
Marker points: Up to 4
Calibration result: Up to 5 groups
Scanning time: 2.7s/every time
Looking at the LiteVNA 64
Frequency range 50kHz ~ 6.3GHz
System dynamic range
>70dB f < 3GHz, calibrated
>50dB f >= 3GHz, calibrated
S11 noise floor
<-50dB f <3GHz, calibrated
<-40dB f >= 3GHz, calibrated
Frequency stability <0.5ppm
Sweep rate >550 points/s Avg=1
Sweep points (on device) 10 ~ 1001 points, adjustable -
Sweep points (USB) 1 ~ 1024 points, adjustable -
Power supply USB, 5V +/- 0.5V 600mA MAX
Battery Li-polymer 3.7V 1300mAh LiteVNA
Operation ambient
temperature -10deg C ~ 50deg C
RF connectors SMA female
Display 3.95"TFT LCD (480x320)
NANOVNA-H4
ABS case: 75mm x 133mm x 18mm (excluding protrusions)
Measurement frequency: 10KHz-1.5GHz
RF output: 0dbm (+-2dbm)
Measurement range: 70dB (50kHz-300MHz), 60dB (300M-900MHz), 40dB(0.9G-1.5GHz));
Port SWR: < 1.1
Display: 3.95 inch TFT (320 x 480)
USB interface: USB type-C communication mode: CDC (serial)
Power: USB 5V 200mA, built-in 1950mAh battery, maximum charging current 1A
Number of scanning points: 101 (fixed)
Display Tracking: 4, Marking: 4, Setting Save: 5
Frequency Tolerance:<2.5ppm
Frequency Stability:<0.5ppm
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I think I'll try out the NanoVNA, and if I like it, I'll return it and buy a LiteVNA64. 😉
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If you download my last user's manual for Solver64 (see dropbox in sig), section 20.0, I talk about the modifications I made to the H4. Shown sweeping from 1.6 to 10kHz after mods.
While this is the best I have seen with these low cost VNAs, it's still not great for power distribution measurements. At best, I would say I can measure the difference between a 1mOhm and 100uOhms, with little accuracy.
If you do at some point feel you need the LibreVNA and want to buy something new, I suggest you have a look at that Pico VNA. The hardware specs look really good. It's a four receiver design. Cost was around $10k USD. At the time their software was not very impressive but that's been several years ago. Sure, 10X the cost but you may find saving up for a much better unit would be better money spent. For now, keep it under $200. Learn how to use it, how not to damage it, what the limitations are....
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I got the 10dB attenuator Mike recommended, and did a bandwidth sweep comparing 3 M&P cables.
1 cable is made by M&P in Italy, using their Stealthflex 7 cable and connectors.
Martin made me a Hyperflex 5 cable, about the same length as the M&P cable.
I made a Hyperflex 5 cable, less than half the length of the others.
It seems the cable length here is likely the reason for the improved flatness compared to the other 2? The longer cables are really close.
This is the short cable:
(https://www.eevblog.com/forum/testgear/cables-connectors-(nsmabnc)-adapters-with-measured-results-for-comparisons/?action=dlattach;attach=2584166;image)
Thanks,
Josh
PS. I received the nanoVNA today...and charged it. That's progress, right?
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Looks like you may only be interested in insertion loss. This thread is similar but OP was asking about impedance.
https://www.eevblog.com/forum/rf-microwave/vna-for-cable-characterization/ (https://www.eevblog.com/forum/rf-microwave/vna-for-cable-characterization/)
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More than 3dB insertion loss at 600MH, you can assume that your setup is the problem. Just to give you something to chew on when for when you get the VNA setup,
Shown is a 74" 50 ohm cable made from Pasternak RG400/U and terminated with HP 1250-0256 BNCs.
https://www.pasternack.com/images/ProductPDF/RG400-U-BULK.pdf (https://www.pasternack.com/images/ProductPDF/RG400-U-BULK.pdf)
To calibrate the setup, I had attached two SMA to BNC adapters. One male, one female. Took a sweep and stored that as the reference (normalizing only). Swapped out the female for a second male then attached the test cable. Not a great setup but gets us in the ballpark.
I ran two tests. One from 1M to 600MHz. You can see at 400MHz I measure an insertion loss of 0.523dB. The cable is spec'ed at 0.555dB. Of course that doesn't account for the connectors or the errors in our cal. But again in the ballpark and a whole lot closer to what I would expect your cables to actually be.
I repeated the test from 1M to 3GHz. At 1HGz we measure and insertion loss of 0.883dB. Cable is spec'ed at 0.888. The ripple is are crap cal. Ignoring that and looking at the worse case 2.679GHz, insertion loss was 2.414dB. At 3dB, the cable is spec'ed at 1.659dB. Considering the poor setup, I would say we are close enough.
You could also try moving the cable around and making sure the graph remains stable.
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More than 3dB insertion loss at 600MH, you can assume that your setup is the problem. Just to give you something to chew on when for when you get the VNA setup,
The scope is 500MHz. What makes you say there's something wrong with the test setup with -3dB at 569MHz?
I did start messing with the VNA. The only thing I've determined for sure is that if I get a real one, I want it to do SA and VNA stuff in one unit.
I made similar cables to test with my power meter, and both the SML and RF power meter were well within spec for accuracy and flatness. Using adapters to test the cables in the test above gives similar results.
Thanks,
Josh
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he meant that what you see in results is more your setup characteristic than the cable itself on that range
as I wrote you back then you are measuring your scopes frontend and ADC
to prove my point even those few key points where the curve has local maximum seems to be in same places just amount of how it goes up/drops down varies
and this is also normal as it is not only cable but connectors even when you exchange single cable only - you press some force on connctors to mount it and this you may see it is so sensitive
that is why for some connctors there are those fancy torque wrenches to tighten em properly
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also with ADC and software "treatment" you could also see some slight variations while repeating the measurements on same cable
(but you would need to set markers on each point of local max and min and note that
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he meant that what you see in results is more your setup characteristic than the cable itself on that range
as I wrote you back then you are measuring your scopes frontend and ADC
Yes, I understand (that part at least 😉). The point of those tests was to measure the effective bandwidth of the scope. I don't consider anything after the -3dB test point particularly useful here. The scope can "bravely" count up to around 930MHz, but I'm ignoring everything over 600MHz anyway.
My curiosities were about the cable & test setup within the scope's bandwidth. What affects that, how to flatten it, etc.
For larger range stuff I would need to use different tools. That's why I'm screwing around with this cheapo VNA, and will probably get a better one eventually.
The wiggles may partially come from the scope frontend/ADC, but certainly better flatness can be achieved, as seen with the attenuator in place.
Thanks,
Josh
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Correct, wrong equipment for the job. It wasn't clear from your post what your goal was.
Personally, I can't see much of an advantage of integrating different tools into one. I guess as long as you get the performance you need. I suspect you would end up with something that can't perform these two tasks very well. I've demonstrated using the LiteVNA directly detecting a local radio station and demodulating the audio as a post process. It was very poor as expected, but I was surprised I could get it to work at all. If I got a new SA, I would go for a real time unit (over swept) but with wider bandwidth than my Signal Hound BB60C. If I were to replace my VNA, I would get another 4-receiver unit with wider range (upper and lower) and faster Ethernet. Maybe 3 ports.
Oscilloscope will be the next thing I replace, if I ever find something I like. It doesn't need to be a logic analyzer, spectrum analyzer, vector network analyzer, power supply, function generator..... just a scope. :-DD
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those small VNA units are surprisingly good, especially when one gets a "better" made unit
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Oscilloscope will be the next thing I replace, if I ever find something I like. It doesn't need to be a logic analyzer, spectrum analyzer, vector network analyzer, power supply, function generator..... just a scope. :-DD
I'm not looking for a single device to do it all.
The scope I want is the SDS5000X HD. I currently have the regular 5000X and the 2000X HD. I like the 2000X HD, but I want higher bw, HDMI out, active probe terminals, external clock input, etc.
I want an SA/VNA combo because it's not something I need at all (just for fun/education), and there are some good options including the Siglent SVA series, or the X-R stuff should be better than my needs for the VNA stuff I'll very rarely use. Even better if I can find somebody that wants to trade one. 😉😉
Thanks,
Josh
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Oscilloscope will be the next thing I replace, if I ever find something I like. It doesn't need to be a logic analyzer, spectrum analyzer, vector network analyzer, power supply, function generator..... just a scope. :-DD
I'm not looking for a single device to do it all.
The scope I want is the SDS5000X HD. I currently have the regular 5000X and the 2000X HD. I like the 2000X HD, but I want higher bw, HDMI out, active probe terminals, external clock input, etc.
I want an SA/VNA combo because it's not something I need at all (just for fun/education), and there are some good options including the Siglent SVA series, or the X-R stuff should be better than my needs for the VNA stuff I'll very rarely use. Even better if I can find somebody that wants to trade one. 😉😉
Thanks,
Josh
lets see how it will work when it comes out regarding the scope
as for VNA better models have sets of probes to check EMC, you can use reflectometry which is very useful thing sometimes when strange things with supposedly new good cable etc
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lets see how it will work when it comes out regarding the scope
It'll be fine. Whatever needs to be fixed, will get fixed.
as for VNA better models have sets of prboes to check EMC, you can use reflectometry which is very useful thing sometimes when strange things with suppsedly new good cable etc
What decent VNA can't do S11?
My needs are very limited anyway. You would probably want something more capable than what covers my needs. You gotta buy the device that meets your needs, not my needs. 😉
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we have a saying that appetite grows with eating and yours develops at pretty fast rate ;)
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we have a saying that appetite grows with eating and yours develops at pretty fast rate ;)
I'll try and take smaller bites. 😉
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:-+
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So, anyway...
I watched Joe's video, and a bunch of Paul's videos, and I have a much better understanding of this stuff. I'll try and do some measurements with the SV4401A I got instead of the nanoVNA-F V2.
The F V2 is too small for me. I found it terribly annoying to work with, and much prefer the full size N connectors on the SV4401A.
BTW- Both of them go to 4.4GHz now. I dunno why they don't advertise that?
Thanks,
Josh
ETA: The SV4401A is trash. It can't stay connected to USB to save it's life. I'm probably going to return both and buy something real.
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I added definitions to run the V3500A power meter and the R&S SMIQ and SML series sig gens with TestController. TestController has a great "Param Sweeper" function, which I used to run these tests going from 10MHz to 6GHz with 10MHz steps (600 total).
First, I ran the test with a nice quality cable going from the V3500A to the UNAT-10A+ attenuator connected at the back of the SMIQ06B (I seriously hate the B19 option; I can't wait to convert it).
Then I removed the cable and tested again with just the attenuator.
Then I ran a full self cal on the SMIQ and Zero on the V3500A.
Finally, I removed the attenuator and connected the meter directly to the SMIQ.
I thought the results were interesting, though mostly expected. I knew the direct connection would be the best. However, I was surprised to see the attenuator wasn't really helpful with the SMIQ. It looks (to me) like it made things worse below 3.5GHz, and really only helped above 5GHz.
Here's the comparison:
(https://www.eevblog.com/forum/testgear/cables-connectors-(nsmabnc)-adapters-with-measured-results-for-comparisons/?action=dlattach;attach=2599597;image)
(for our colorblind friends, the legend from left to right matches the plotlines from bottom to top)
I'm going to run the direct tests with and without the attenuator on the SML03 for comparison.
Thanks,
Josh
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I thought the results were interesting, though mostly expected. I knew the direct connection would be the best. However, I was surprised to see the attenuator wasn't really helpful with the SMIQ. It looks (to me) like it made things worse below 3.5GHz, and really only helped above 5GHz.
Here's the comparison:
In TC you can use any value for x-axis, not only time, try right clicking on the hh:mm:ss text at the bottom. You can select a log scale if you want.
You can also combine curves from different files with the import function.
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I returned that SV4401A, and ordered one from another reseller to rule out a hardware fault. Of course, it was all the same. No reliable connection.
Today I found Sysjoint released a new firmware version for the SV4401A, and a custom version of the nanoVNA App. It works now. Shocking, right?
Anyway...
I want to make a comparison to the M&P provided test. How do I need to setup the nanoVNA to match their test? Or is their test result questionable?
I tried testing the cable 50Ω terminated, and connected to port 2 (full calibration done including through).
From their equipment range and description, I'm assuming they're also using some version of the nanoVNA, maybe the SAA2. I dunno though. Is SRL the same as RL, or is there something else I'm missing here?
Thanks,
Josh
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...
Today I found Sysjoint released a new firmware version for the SV4401A, and a custom version of the nanoVNA App. It works now. Shocking, right?
...
Just to make sure. Avre you talking about SV4401A or nanoVNA when you say it works now?
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...
Today I found Sysjoint released a new firmware version for the SV4401A, and a custom version of the nanoVNA App. It works now. Shocking, right?
...
Just to make sure. Avre you talking about SV4401A or nanoVNA when you say it works now?
The SV4401A is a nanoVNA variant. I'm talking about the SV4401A, and a custom Sysjoint released version of the nanoVNA app. The SV4401A still won't work with the "official" releases of the apps (at least not for me on Win11), but hopefully that will be rectified eventually also.
I'm happy to use it with the custom nanoVNA app, and the SVXX01A-Tools app is cute too if you want to control the SV4401A the same on your computer as it looks on the device.
New fw: https://www.sysjoint.com/ueditor/php/upload/file/SV4401A_App_v0.7.0.zip (https://www.sysjoint.com/ueditor/php/upload/file/SV4401A_App_v0.7.0.zip)
Sysjoint nanoVNA-App: https://www.sysjoint.com/ueditor/php/upload/file/NanoVNA-App_by_SYSJOINT.zip (https://www.sysjoint.com/ueditor/php/upload/file/NanoVNA-App_by_SYSJOINT.zip)
SVXX01A-Tools: https://www.sysjoint.com/ueditor/php/upload/file/SVXX01A_Tools.zip (https://www.sysjoint.com/ueditor/php/upload/file/SVXX01A_Tools.zip)
Thanks,
Josh
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Now it's much clearer.
So you use the Sysjoint custom nanoVNA app with your second SV4401A and it's working. Got it.
I've been thinking about getting one to play with, but the only feedback about it was your thread here and it wasn't positive.
Might give it a shot now.
My Agilent N9340A doesn't have a lot of the functionality of these cheap chinese units, but at least I can compare the two (as a sanity check).
I also need to do something about it's dim display (N9340a that is), but haven't gotten around to it yet.
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I think all SV4401As are the same, and made by Sysjoint. I did not like dealing with ARSINC (pronounced Arse Inc.), and they charge more than other suppliers. The 2nd one I got was $319 (instead of $499 from ARSINC), both on Amazon.
I also have an SAA2N, though sanity checking isn't the best going between two very similar devices, but still better than nothing. I hope to get a Siglent VNA eventually.
Thanks,
Josh
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I've been eyeing Siglent's SHA850 & SHA860 series, just can't justify the price for a hobby. ;D
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lol, I don't think I'm worthy of that one either. 🤣
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I still don't know how to convert S11 to SRL, so I'll ignore the M&P test sheet for now.
I assume these are more relevant to the tests we're doing with our scopes anyway.
Thanks,
Josh
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I'm a little puzzled by the screenshots. Is that a 1-port measurement or 2-port? Are you measuring insertion loss or return loss? Numbers don't make sense???
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I'm a little puzzled by the screenshots. Is that a 1-port measurement or 2-port? Are you measuring insertion loss or return loss? Numbers don't make sense???
S11 is always 1 port. It's easier to see on the attached graph. For example, at 500MHz, attenuation is -0.29dB, and at 600MHz attenuation is -0.32dB. This is useful when doing the fun FFT bandwidth tests on a 500MHz scope, because I know that if I go to exactly the -3dB point on the scope, I'm actually not showing the true -3dB point because 10% of that attenuation is coming from this specific cable.
I highly recommend watching some or all of Paul's videos on VNAs: https://www.youtube.com/watch?v=rUDMo7hwihs&list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8&index=1 (https://www.youtube.com/watch?v=rUDMo7hwihs&list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8&index=1)
I didn't understand any of this stuff before I watched some of these...2 or 3 times. 🤣
Thanks,
Josh
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Here's a comparison of 3 cables (S11 cable loss). I couldn't figure out how to move marker labels (maybe not possible?), or any option to show the memory labels. Does anybody know how to do that in nanoVNA-App?
Green = short Hyperflex 5
Orange = Stealthflex 7
Purple = long Hyperflex 5
(https://www.eevblog.com/forum/testgear/cables-connectors-(nsmabnc)-adapters-with-measured-results-for-comparisons/?action=dlattach;attach=2603293;image)
Thanks,
Josh
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https://blog.teledynelecroy.com/2020/05/reading-s-parameters-ripples.html
https://blog.teledynelecroy.com/2014/12/what-s-parameters-reveal-about.html
https://blog.teledynelecroy.com/2014/12/what-s-parameters-reveal-about_9.html
https://blog.teledynelecroy.com/2014/12/what-s-parameters-reveal-about_17.html
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That's the part I'm having trouble with. Are the cables that you are testing terminated with 50 Ohm load?
Because this is what i'm getting with my Agilent N9340A using a directional coupler from Mini-Circuits part #ZFDC-20-4-N+, measuring Agilent cable part #15NNF50-1.5A
Open:
[attachimg=1]
Terminated with 50 Ohm Mini-Circuits load part #KARN-50-18+:
[attachimg=2]
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No load. Paul's video said to test either open or shorted at the other end, so I left them open.
What's the directional coupler for?
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I was measuring cable loss, based on this video:
https://www.youtube.com/watch?v=xqLQH0eWs3E&list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8&index=9 (https://www.youtube.com/watch?v=xqLQH0eWs3E&list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8&index=9)
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Ok, now I know why it didn't make sense to me ;D
If you don't terminate it the other end, almost everything is reflected back, so your return loss is huge.
That's why your VSWR is off the charts.
You need to terminate it to know how much power is reflected back. It should look more like the second picture in my previous post.
Since Agilent N9340A can't make one port measurements, I need a directional coupler to measure the reflected power.
Idealy your return loss will be -30dbm or more. The closer your get -50dbm to closer you are to "ideal" load.
I have not had good results using one port measurements for cable loss.
I just use two ports to measure insertion loss.
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lol, yeah, I guess it's good I left the VSWR in that graph so I could learn how to do that too...eventually. 😉😉
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How's this look? The 50Ω termination is crap. I had to use an N-N through with the 50Ω cal load.
Thanks,
Josh
ETA: I have some Amphenol 50Ω terminators for N, BNC, and SMA in my Mouser cart.
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That's more like it 😁
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Can somebody explain this one? What's different here between the S11 logmag (cable loss?) vs Coax Loss?
Thanks,
Josh
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Not having that particular device, I'm not certain.
But for cable loss, I personally would not use S11.
I would use S21 (2-port) measurements.
That way after you normalize/calibrate/zero out your device, you are measuring the actual cable loss.
For a decent coax, the loss @ 2GHz should be way under 1db (for few feet/around a meter).
I'll let someone with more knowledge about your VNA interpret the screenshots.
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My understanding on this stuff is quite limited, however...whether measuring S11 or S21 the device should be calibrated appropriately.
I will try to do an S21 transmission test, but doing that in this case is difficult because the cables go from N to BNC, and it's hard to calibrate the Thru right now. I did make a DUT cable for this, let's see how it works out. 🤔
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Here's an S21 test. I don't trust it though since the DUT cable is lower quality than the cable being tested...and I dunno if it's calibrated out properly.
The image with two traces is comparing the same cable with the VNA calibrated differently, and the cable reversed. Blue is with a DUT cable on port 2 calibrated out with a crappy through, and the white trace is with the crappy adapter calibrated out on port 1 instead.
Thanks,
Josh
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do you have any N to N connector cable at hand to make the test on it?
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do you have any N to N connector cable at hand to make the test on it?
Yes, but please describe exactly what you want me to test, and how I should calibrate it first.
Thanks,
Josh
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That looks more like what a cable loss measurement shoud be.
All those dips & peaks are reflections caused in the connectors and difference in velocity of propogation of different cable types.
You want a pretty good quality cable to connect the two ports of the VNA for calibration/normalization, so that measurement plane is at the end of the cable.
That way when you measure your DUT cable, any loss is in the DUT and not in the setup.
Again, I'm not familiar with your VNA, so I can't help with propper calibration procedure.
On the Agilent it's pretty straight forward to normalize the cables/through/etc. for a propper setup.
Once I get myself one of those VNA's, I'll post back with what it looks like on my end.
Give me a few days ;D
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The DUT cable I'm referring to is a cable connecting the VNA to the DUT, which in this case (the DUT) is also a cable. 😉
My question isn't about this VNA specifically, but about calibration in general on a two-port VNA. If you have two DUT cables to connect the DUT (in this case, a cable), and a high-quality pass-through adapter, it's pretty straight forward.
But if I want to test with a single adapter or single DUT cable, it becomes trickier to calibrate those things out. It will be easier once I order the other calibration adapters...but this does get a little ridiculous.
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Just for reference, this is what the above cable looks like when I do S21 measurement:
[attachimg=1]
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I know what you mean ;D
If you want to measure a cable, I wouldn't use 2 cables for calibration.
I would calibrate with one cable for OSL & connect that same cable to the second port for a through.
That way your measurement plane will be at the connector of the second port, to which you connect DUT cable to test.
Idealy you would not use any gender adapters, but even if you do, they should not introduce too much loss (if they are from a reputable manufacturer).
And the adapter loss should be stated in the datasheet.
In my experience, N adapters have a loss of 0.1db to 0.4db depending on frequency (up to 3GHz).
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I know what you mean ;D
If you want to measure a cable, I wouldn't use 2 cables for calibration.
I would calibrate with one cable for OSL & connect that same cable to the second port for a through.
That way your measurement plane will be at the connector of the second port, to which you connect DUT cable to test.
Idealy you would not use any gender adapters, but even if you do, they should not introduce too much loss (if they are from a reputable manufacturer).
And the adapter loss should be stated in the datasheet.
In my experience, N adapters have a loss of 0.1db to 0.4db depending on frequency (up to 3GHz).
Right, I want to set up the DUT cable on port one, but since the cables I'm testing are N to BNC, so is the DUT cable (but with female BNC), and that requires an adapter to connect to the 2nd N port. That means I need a male BNC calibration kit, right? I don't have that yet. I'm going to order some BNC loads to try, but I'm not going to spend a lot of money on this. Close enough is good enough. 😉
IME, the adapters add reflections and loss.
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Just for reference, this is what the above cable looks like when I do S21 measurement:
Assuming any accuracy on my S21 test, that's double the attenuation compared to the Stealthflex 7 cable I tested. Can you adjust the scale to show more detail?
Thanks,
Josh
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That means I need a male BNC calibration kit, right?
You need OSL at the end of the cable on port 1 (the transmit port). So if it end with a male BNC, you would need female BNC OSL or vice versa.
IME, the adapters add reflections and loss.
Absolutely, especially between diferent types of connectors.
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You need OSL at the end of the cable on port 1 (the transmit port). So if it end with a male BNC, you would need female BNC OSL or vice versa.
Exactly. The DUT cable is male N to female BNC, so I'll need male BNC OSL, but I'm going to get female also, cause who knows what stupid thing I'll do next. ;)
The problem is, I'll want to make a nicer DUT cable after I do those things. :palm:
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Sure. The lowest I can go is 1db/div.
Frequency range is 100kHz to 3GHz
[attachimg=1]
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Sure. The lowest I can go is 1db/div.
Seriously? That kinda sucks. Shame on you, Agilent! ;)
The nanoVNA App / device can both go to some fairly ridiculous scales.
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Sure. The lowest I can go is 1db/div.
Seriously? That kinda sucks. Shame on you, Agilent! ;)
The nanoVNA App / device can both go to some fairly ridiculous scales.
Yup, so can the SVA1032X you want however you should well know resolution does not equal accuracy.....for that we must consult datasheets. ;)
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Yup, so can the SVA1032X you want however you should well know resolution does not equal accuracy.....for that we must consult datasheets. ;)
Thanks, Captain Obvious. 😉😉
Datasheets don't account for bad accuracy due to my dumbass screwing up the test setup and/or calibration. 🤣
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It was suggested to me to calibrate both ports, and so I did. I used a different DUT cable, with an assumed higher quality N-BNC adapter. Attached are the results.
Is that a normal thing? Do people calibrate both ports on their VNAs? What's the process normally like if you do?
Never mind. Unless I'm wrong, that's only useful for VNAs that can do more than S11 and S21.
Thanks,
Josh
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Looks good ;D
You are correct, 2-port calibration is performed if both ports can transmit.
I'm with you on your previous question:
What are they showing under "Coax Loss" graph???
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Two tests of my SDG6052X.
Chart 1 is using a nice HF5 cable.
Chart 2 is direct connection through a cheap adapter.
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I'm exploring this again now that I have access to a real VNA. Both ports were OSL calibrated.
Here's the StealthFlex7 N to BNC cable again. Still using a crap adapter and no through cal.
This looks more believable, right?
Thanks,
Josh
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This is a short blue cable that came with a nanoVNA. This seems really good, right?
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This is a short blue cable that came with a nanoVNA. This seems really good, right?
I'd be more concerned about the rather large S21 ripple. This can mean that there are are discontinuities in the cable (reflections at the cable-connector transitions), or that the calibration is not very precise (the effective source and load port match is off, hence the VNA sees discontinuities with respect to the cable).
Attached is the S21 and S11 of a Huber+Suhner Sucoflex 106 (blue traces) and a Sucoflex 104 (red traces) microwave cable. The 106 is almost double the length of the 104, as you can see from the S11 ripple. The load in the cal kit is well below -40 dB return loss when measured against an known-good reference kit, so these ripple are within the dynamic range of the measurement. Overall, this is a good result for a high-quality microwave cable.
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This is a short blue cable that came with a nanoVNA. This seems really good, right?
I'd be more concerned about the rather large S21 ripple.
No need to be when Josh has just discovered what happens when you don't do a full SOLT Cal and then do a through measurement.
I'm exploring this again now that I have access to a real VNA. Both ports were OSL calibrated.
When you shift scaling to mdB these things start showing up. :scared:
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For comparison a random cheap SMA cable of unknown origin. The shape of the S21 trace depends heavily on the bending, and is not even monotonic with frequency. The matching at the cable end is not too bad (|S11| remains below -20 dB), but it has a loss as big as 3.5 dB at certain frequencies. So either a very lossy dielectric, or the cable radiates at these frequencies because the shielding is crappy.
Btw.: The calibration was a two-port unknown thru (UOSM), with the cal planes in the adapters on the VNA ports.
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When you shift scaling to mdB these things start showing up. :scared:
But they require an explanation if one wants to measure precisely in this area. Which is perfectly feasible with the appropriate means. ;)
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I guess I need to use more cables/adapters so I can do the through cal also. Fiiiiiiiiiiiiiiine. But it's a pain in the ass because I don't have any really good DUT cables. We'll see what happens I guess. ;)
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When you shift scaling to mdB these things start showing up. :scared:
But they require an explanation if one wants to measure precisely in this area. Which is perfectly feasible with the appropriate means. ;)
100%
But a S21 is a through measurement so to do it accurately a through needs be part of the VNA Cal.
I guess I need to use more cables/adapters so I can do the through cal also. Fiiiiiiiiiiiiiiine. But it's a pain in the ass because I don't have any really good DUT cables. We'll see what happens I guess. ;)
It's only when you open the rabbit hole of mdB measurements you see these things.
Although not an RF expert it didn't take me long to work out what cabling was to be the most useful and which Cal kit (M or F) to get so to Cal at the DUT.
Your new to you SNA has some pretty neat features for Port extensions and such to enhance accuracy further and remove discontinuities', reflections and such.
Mine lives with member hendorog whom is away for a few days but I'll point him here for some comments to give you a better understanding of this VNA's capabilities.
Check out his Cal kits:
https://vnalab.net/
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When you shift scaling to mdB these things start showing up. :scared:
But they require an explanation if one wants to measure precisely in this area. Which is perfectly feasible with the appropriate means. ;)
100%
But a S21 is a through measurement so to do it accurately a through needs be part of the VNA Cal.
It wasn't immediately clear to me that he hadn't performed a full two-port calibration. :)
I guess I need to use more cables/adapters so I can do the through cal also. Fiiiiiiiiiiiiiiine. But it's a pain in the ass because I don't have any really good DUT cables. We'll see what happens I guess. ;)
I just looked at the datasheet of the SNA5000A series VNA and they seem to be able to perform unknown-thru calibrations. So assuming your cable is reciprocal (which it is), you can use the cable under test itself to do the thru step of your calibration.
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Mine lives with member hendorog whom is away for a few days but I'll point him here for some comments to give you a better understanding of this VNA's capabilities.
Check out his Cal kits:
https://vnalab.net/
I've looked at his site before a few times, but I've never seen N stuff there. I know you prefer SMA, but I want N and SMA cal kits. I'd like a Siglent F504TS to magically appear on my bench. ;)
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It wasn't immediately clear to me that he hadn't performed a full two-port calibration. :)
I may have mentioned it once or twice. I usually know when I'm doing something stupid. ;)
I just looked at the datasheet of the SNA5000A series VNA and they seem to be able to perform unknown-thru calibrations. So assuming your cable is reciprocal (which it is), you can use the cable under test itself to do the thru step of your calibration.
That's crazy. How does that work? Do I use the cable for the through, and then just run S21, or do I need to use one of those fancy features I haven't properly tried yet?
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That's crazy. How does that work? Do I use the cable for the through, and then just run S21, or do I need to use one of those fancy features I haven't properly tried yet?
Yes, if your VNA supports that, you can use the cable as a thru, and then simply run a S21 measurement. That's what I did in the measurements I posted above -- the DUT is the thru. R&S calls that UOSM, but this method is also known as unknown thru or SOLR (short-open-load-reciprocal). It relies on the assumption that the 2-port device used as a thru is reciprocal, which is true for a cable. It was first published in 1992 in an IEEE Microwave and Guided Wave Letters volume by A. Ferrero and U. Pisani.
The method is based on the 8-term error model for VNA measurements (using error two boxes at each port, each described by ABCD-parameters), and this error model can be converted to the usual 12-term error model by using additional measured quantities, the so-called switch terms. These are the ratios of the incoming and outgoing wave amplitudes at one port while the other port is used as a source. This requires the VNA hardware to have four receivers (in a two-port VNA).
Sounds magical, but it works. :) At first sight, the math behind it is a bit confusing though.
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Mine lives with member hendorog whom is away for a few days but I'll point him here for some comments to give you a better understanding of this VNA's capabilities.
Check out his Cal kits:
https://vnalab.net/
I've looked at his site before a few times, but I've never seen N stuff there. I know you prefer SMA, but I want N and SMA cal kits. I'd like a Siglent F504TS to magically appear on my bench. ;)
Request a N type of the gender you prefer and he'll price something and give you an ETA.
hendorog likes to characterize every Cal kit to see what he's getting and know buyers will be satisfied for their spend.
BTW he discovered where F504TS is made and now buys direct to undercut what we can provide them for......I don't care and prefer he handles this RF stuff as it is pretty specialised and I'm not about to shell out for a 20+ GHz VNA like he has.
I do know he'd prefer a SNA6134A but neither of our pockets are that deep ! :scared:
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That's crazy. How does that work? Do I use the cable for the through, and then just run S21, or do I need to use one of those fancy features I haven't properly tried yet?
Yes, if your VNA supports that, you can use the cable as a thru, and then simply run a S21 measurement. That's what I did in the measurements I posted above -- the DUT is the thru. R&S calls that UOSM, but this method is also known as unknown thru or SOLR (short-open-load-reciprocal). It relies on the assumption that the 2-port device used as a thru is reciprocal, which is true for a cable. It was first published in 1992 in an IEEE Microwave and Guided Wave Letters volume by A. Ferrero and U. Pisani.
The method is based on the 8-term error model for VNA measurements (using error two boxes at each port, each described by ABCD-parameters), and this error model can be converted to the usual 12-term error model by using additional measured quantities, the so-called switch terms. These are the ratios of the incoming and outgoing wave amplitudes at one port while the other port is used as a source. This requires the VNA hardware to have four receivers (in a two-port VNA).
Sounds magical, but it works. :) At first sight, the math behind it is a bit confusing though.
Thank you! That was very helpful. It looks like the advanced cal options make it so I can do SOLR and then change the R later, or do SOL and add R later too. Noice.
How do the attached charts look now?
Thanks,
Josh
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[BTW he discovered where F504TS is made and now buys direct to undercut what we can provide them for...
Oooh, now that's interesting. I'm gonna have to email or message him. Thanks, Rob!
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How do the attached charts look now?
Looks absolutely great. Even though there's a bit more trace noise than with the R&S. But I guess that's the difference between a € 6.000 and a € 60.000 VNA. ;)
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I wouldn't mind having an R&S FPL to play with also. Both are way out of my league though. :-DD
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Looks absolutely great. Even though there's a bit more trace noise than with the R&S. But I guess that's the difference between a € 6.000 and a € 60.000 VNA. ;)
What are your other settings, like RBW set to? Averaging? How many points are you testing at? Do you have any smoothing applied? I have mine set to 20001 points with no smoothing.
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How do the attached charts look now?
Looks absolutely great. Even though there's a bit more trace noise than with the R&S. But I guess that's the difference between a € 6.000 and a € 60.000 VNA. ;)
Recent discussions with hendorog have been about this.....
Tests of what the HW can do for him with HPAK, CM, SNA5004A and his X-R VNA's have been very interesting and spurred him to add a smoothing feature (not averaging) in the VNA SW package he's been developing.
Apparently single pixel traces are on the way ! :o
It's a totally private development that I get to test a little as it can report if there is a new version and autoupdate on command.
It's in a fairly advanced stage now and primarily collects the raw data from a VNA over LAN or GPIB and crunches it on a PC to offer more capability than what a VNA can provide.
A wee introduction and screenshot is here:
https://www.eevblog.com/forum/testgear/siglent-sva1015x-1-5ghz-spectrum-vector-network-analyzer-(coming)/msg6243401/#msg6243401 (https://www.eevblog.com/forum/testgear/siglent-sva1015x-1-5ghz-spectrum-vector-network-analyzer-(coming)/msg6243401/#msg6243401)
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What are your other settings, like RBW set to? Averaging? How many points are you testing at? Do you have any smoothing applied? I have mine set to 20001 points with no smoothing.
From memory, I think it was set to 200 Hz RBW and 601 points, 0 dBm source power, with no averaging or smoothing filters applied. But the ZVB generally has an extremely low trace noise, and a dynamic range well above the published specs.
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From memory, I think it was set to 200 Hz RBW and 601 points, 0 dBm source power, with no averaging or smoothing filters applied. But the ZVB generally has an extremely low trace noise, and a dynamic range well above the published specs.
Here's two for comparison. One with 20001 points, 30kHz RBW, and one with 601 points, 200Hz RBW. Both with a touch of smoothing applied. I'd say that's good enough for me. ;) ;)
Thanks,
Josh
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Here's two for comparison. One with 20001 points, 30kHz RBW, and one with 601 points, 200Hz RBW. Both with a touch of smoothing applied. I'd say that's good enough for me. ;) ;)
Looks very good. Also for comparison: Both channels set to 601 points. Channel 1 is at 100 kHz IFBW (which yields 54.09 ms sweep time), channel 2 is at 100 Hz IFBW (which yields 12.06 s sweep time). No averaging or smoothing is applied. Both channels are calibrated with the unknown thru method, the DUT is again the Sucoflex 104 cable.
You can see a bit of trace noise with 100 kHz IFBW if you zoom in, but at 5 dB/div that would be invisible. Also you can see a small discrepancy between the two S21 traces. That might be because the two calibrations of channel 1 and 2 were done with separate connections of the cal standards. At 0.08 dB/div things like temperature and connector torque start to matter (I didn't use a torque wrench and only tightened them hand-tight.).
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That might be because the two calibrations of channel 1 and 2 were done with separate connections of the cal standards. At 0.08 dB/div things like temperature and connector torque start to matter (I didn't use a torque wrench and only tightened them hand-tight.).
Yep, if you carry the calibration of channel 2 over to channel 1, the two S21 traces agree much better, so it very likely is connector repeatability when connecting the cal standards. But you do get some ripple from transplanting the calibration.
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Thanks! Your posts are informative and helpful for learning this stuff.
Why do you select 601 points in this range?
Thanks,
Josh
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Josh,
You need to get real cables from Gore!!
https://www.gore.com/products/vna-microwave-rf-assemblies?xcmp=hdr-all_aero_ppc_aad_google_NA%7C%7Cgore-cables-branded (https://www.gore.com/products/vna-microwave-rf-assemblies?xcmp=hdr-all_aero_ppc_aad_google_NA%7C%7Cgore-cables-branded)
Best
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You need to get real cables from Gore!!
Quit it! :-DD :-DD :-DD
I have real cables from Messi & Pauloni, and I won't be spending anything higher than that. I've already spent more on cables from them than my previous two VNAs cost combined. ;)
The cable I'm testing is a shitty free cable, but that's on purpose. I do have some more stuff coming from M&P also though, including a nice N to N cable they're making for me. I'll test that when I get it. I'll also make a couple N to N cables myself for comparison with solder and crimp versions. The nicer cables I have are N to BNC.
Thanks,
Josh
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Why do you select 601 points in this range?
When you only want to look at, say, a plot of the S21 magnitude and things don't vary rapidly with frequency, using more frequency points doesn't help much but increases sweep time. After all, your screen resolution is limited. This may be different when things like the phase changes rapidly with frequency and you want to plot that, or look at the Smith chart, and the curve becomes angled. But that's not the case with a piece of cable, which should have a flat group delay.
You may also need a lot more points when you want to do some specific post-processing of the S-parameter data, like converting to the time domain. Then the number of points is directly related to the maximum ambiguity-free electrical length of your setup.
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This is a different short N to N cable. What do you think about this one? How do you think this cable compares to the other one?
Thanks,
Josh
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This is a different short N to N cable. What do you think about this one? How do you think this cable compares to the other one?
If the results are for real I'd call that cable defective. Around 3 GHz you have a S21 ripple with almost 2 dB amplitude (pp). That could be explained by two impedance discontinuities along the cable (e.g., at the ends) of about -9.4 dB return loss if you do the math, assuming they are both equal. With two such discontinuities at -10 dB return loss each, the reflections would add up to about -4 dB worst case (constructive interference), which corresponds roughly to the peaks of the S11 ripple near 3 GHz. So what you show is consistent with two discontinuities of about -10 dB return loss near 3 GHz.
You could check if the frequency Δf between two ripple peaks corresponds to the electrical length L of the cable, from L = kc/2Δf, where k is the velocity factor of the cable. With k = 0.7 and ΔF = 280 MHz (the 2 in the denominator accounts for the round trip of the reflected wave in the cable) this yields L = 0.38 m. Is that your cable length? That would mean the discontinuities are at the ends.
So either your calibration is off, or you have some serious defects along the cable, e.g., incorrectly mounted connectors. A good cable should have a |S11| below -25 dB and only minimal S21 ripple.
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If the results are for real I'd call that cable defective. Around 3 GHz you have a S21 ripple with almost 2 dB amplitude (pp). That could be explained by two impedance discontinuities along the cable (e.g., at the ends) of about -9.4 dB return loss if you do the math, assuming they are both equal. With two such discontinuities at -10 dB return loss each, the reflections would add up to about -4 dB worst case (constructive interference), which corresponds roughly to the peaks of the S11 ripple near 3 GHz. So what you show is consistent with two discontinuities of about -10 dB return loss near 3 GHz.
You could check if the frequency Δf between two ripple peaks corresponds to the electrical length L of the cable, from L = kc/2Δf, where k is the velocity factor of the cable. With k = 0.7 and ΔF = 280 MHz (the 2 in the denominator accounts for the round trip of the reflected wave in the cable) this yields L = 0.38 m. Is that your cable length? That would mean the discontinuities are at the ends.
So either your calibration is off, or you have some serious defects along the cable, e.g., incorrectly mounted connectors. A good cable should have a |S11| below -25 dB and only minimal S21 ripple.
That's what I thought (crappy cable). It was a short one I made last year, but I definitely screwed up the connectors. Yes, your length estimate is correct as well.
Attached is another cable I made, but much longer, and also a little better. I redid one of the connectors yesterday to change the gender from F to M, and I assume that also improved the quality of the connection since I'm better at those now than I was a year ago. ;)
Should I redo the other end, or do you think this looks good? Keep in mind it's Hyperflex 5, which they don't recommend above 2.4GHz.
Thanks,
Josh
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This is that same "better" cable. I did a full SOLR cal before each of the screenshots, switching the direction of the cable for R.
I swapped the direction to see if this is a valid test of the connector quality at either end of the cable.
Am I correct that the S11 readings on "Old to new" are less desirable than those on the "New to old" screenshots?
If so, I assume I should redo the Old connector to improve the cable. Is that correct?
Thanks,
Josh
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Yes, the "New to Old" is slightly better, but not by much.
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Yes, the "New to Old" is slightly better, but not by much.
Thanks, that's what I thought. Is it enough to bother redoing? Or do you think they should both be improved? Or leave them alone?
Thanks,
Josh
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Looking at their datasheet, they don't list any specs regarding return loss above 2GHz. And return loss between 1.2GHz & 2GHz is ">22db", whatever that means :-//
I personally wouldn't use it for anything above 1-1.2GHz to do any critical measurements. I've played with M&P coax in amateur radio setting, but would not call it "test equipment grade" cable.
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They have different grades of cable, but their datasheets are a little weird. I think they might be at the top end of what I'm willing to spend on cables though. It's also worth noting that nothing I'm doing requires anything better than $20 generic cables.
I'm sure the $5000 Gore cables Mike suggested are a little better. ;)
What do you use?
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Cables Mike linked sure are nice, but I'm not shitting $$$ :-DD
I scrounge eBay for good deals on similar (not quite as good) cables. Also, some of the equipment I have bought, came with realy nice cables.
Right now there are couple of cables available (no affiliation):
https://www.ebay.com/itm/227309779780 (https://www.ebay.com/itm/227309779780)
If I have to make my own and they are not going to be very long, I use RG400. Even chinesium stuff is relatively consistent in performance and you can use good connectors for rg58 on it.
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I'm happy with the M&P stuff, I just need to do a better job than that other shit cable I made. I think that was maybe the worst one I did- that's why I tested it.
I will have a better idea on the M&P quality soon though. They're making me an N cable with their Sahara 10 cable, which is rated much higher than the other cables I have. I'm looking forward to seeing how that looks on my VNA. I can't test my other good cables because they're N to BNC, and I want the S21 chart like Mario showed above.
If I can get a good deal on one of the cables you linked, I'd love to test it for comparison...but generally speaking, that's 3 times the price I would want to pay for a cable. Now that I think of it, I'm going to get some longer cheap cables to compare also. ;)
Thanks,
Josh
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No worries ;D
My biggest issue with M&P cables is except for their "whatever 10" stuff and "airborn5" cables. none of the other cables they make is compatible with standard/regular connectors.
The Hyperflex 5 for example is .212 diameter, so you can't use none of the .195/200 connectors on it or the .240 connectors, so you have to use whatever connectors they sell.
And I think (from my experience, no imperical evidence) that their connectors aren't that good at higher frequencies.
Just my $.02 cents
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Tools for the job. ;)
For me, the Hyperflex 5 was an excellent upgrade compared to other cables when doing bandwidth tests on my oscilloscopes. None of my scopes have gone to or over 1GHz though. I always got a higher -3dB point with the M&P cables compared to anything else I tried. IME I think their quality is good for their pricing.
Hyperflex 5 isn't rated for higher frequencies over 2 or 2.4GHz, but it's not terrible either. I'll test it higher to see what it looks like. The only sorta issue is that my cal kit is only rated to 4.5GHz, so I dunno how good it will look above that regardless.
I find other things about M&P weird. Like they had N crimp connectors for 5 and 10, but not 7 series cables.
For people like you and Mario that are more serious about RF, I can see budgeting higher priced/quality cables. Makes no sense for me when this is 95% academic and 100% a waste of money...though I might have ordered a pre-owned Huber+Suhner Sucoflex 104 cable to compare. :-DD
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Tools for the job. ;)
Yup, 100%
For me, the Hyperflex 5 was an excellent upgrade compared to other cables when doing bandwidth tests on my oscilloscopes. None of my scopes have gone to or over 1GHz though. I always got a higher -3dB point with the M&P cables compared to anything else I tried. IME I think their quality is good for their pricing.
That's been my experience also. My highest bandwidth oscilloscope is an analog-ish LeCroy/Iwatsu @ 470MHz, so my tests have been done using VNA's & SA's
I find other things about M&P weird. Like they had N crimp connectors for 5 and 10, but not 7 series cables.
Yup, makes no sense :-//
Makes no sense for me when this is 95% academic and 100% a waste of money...though I might have ordered a pre-owned Huber+Suhner Sucoflex 104 cable to compare. :-DD
>:D
:-DD
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>:D
:-DD
Yup, another point for you. Don't worry- I'll get you again! :-DD :-DD :-DD
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I posted this cable test procedure a while ago. It comes from Dr Joel Dunsmore - who pops up here from time to time.
https://www.eevblog.com/forum/testgear/cables-and-connectors-for-vna-lt-3-ghz/msg2444583/#msg2444583 (https://www.eevblog.com/forum/testgear/cables-and-connectors-for-vna-lt-3-ghz/msg2444583/#msg2444583)
With VNA cables, normally the priority is stability and being free of faults. Within reason the absolute performance in Return Loss and Through Loss is not as important.
As an aside, I discovered I had a fault in a cable using TDR on SNA a while ago.
(See attached DTF mode pic from the recently repaired SSA which I had handy)
I terminated the far end of the cable, and the trace shows a spike about 2/3rds of the way along the cable.
This was one of a pair of Siglent (Rosenberger) N-SMA cables that have seen a bit of travel, so it may have had a minor mishap (bent) at some stage.
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I posted this cable test procedure a while ago. It comes from Dr Joel Dunsmore - who pops up here from time to time.
Can you pretty please demonstrate that method using the SNA5000A Rob gave you? ;) ;)
Thanks,
Josh
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I posted this cable test procedure a while ago. It comes from Dr Joel Dunsmore - who pops up here from time to time.
Can you pretty please demonstrate that method using the SNA5000A Rob gave you? ;) ;)
Thanks,
Josh
That is good to hear, sounds like he doesn't want it back!!! :-+ :popcorn:
I'll take some pics.
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Pop quiz: How much did this 2 meter cable cost? ;)
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No clue, but looks like s***t :-DD
One thing I'm forgetting to ask. Are you testing them as a through (both end connected to the vna) or single ended (as if it were an antenna)?
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No clue, but looks like s***t :-DD
I'd say that's a clue. 🤣
One thing I'm forgetting to ask. Are you testing them as a through (both end connected to the vna) or single ended (as if it were an antenna)?
Doesn't the S21 measurement answer your question? ;) ;)
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I posted this cable test procedure a while ago. It comes from Dr Joel Dunsmore - who pops up here from time to time.
Can you pretty please demonstrate that method using the SNA5000A Rob gave you? ;) ;)
Thanks,
Josh
That is good to hear, sounds like he doesn't want it back!!! :-+ :popcorn:
:-DD
You paying for our Siglent HQ trip and hotel costs later this year ? :P
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I posted this cable test procedure a while ago. It comes from Dr Joel Dunsmore - who pops up here from time to time.
Can you pretty please demonstrate that method using the SNA5000A Rob gave you? ;) ;)
Thanks,
Josh
That is good to hear, sounds like he doesn't want it back!!! :-+ :popcorn:
:-DD
You paying for our Siglent HQ trip and hotel costs later this year ? :P
More money in test gear sales than cal kits fella :clap:
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:-DD :-DD :-DD
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Doesn't the S21 measurement answer your question? ;) ;)
Brain fart |O
I need to stop reading/looking at things before my first cup of coffee :)
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Serves you right for getting me to buy two different H+S cables. :-DD :-DD :-DD
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Serves you right for getting me to buy two different H+S cables. :-DD :-DD :-DD
I'm pleading the Fifth ;D
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Here's that new M&P cable (Hyperflex 10 Sahara). Whattayathink?
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This is the Stealthflex 7 cable I made with crimp N connectors.
This was a little funny. I thought I did something wrong since I ordered 3 meters, and DTF was saying it's 4 meters long. After triple checking my settings, my daughter helped me measure the cable. The VNA was correct. M&P sent me an extra meter for free. :-DD
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They look OK.
But I still wouldn't use them above around 2GHz or so.
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They look OK.
But I still wouldn't use them above around 2GHz or so.
Sure, but they don't really recommend that on them either (at least not the thinner ones). For non-critical measurements, they're fine anyway. I might do some sweeps and see what it looks like. Also compare the prices to the Sucoflex 104 or higher, and they're definitely worth it. ;)
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
Visual or analytic ?
Pretty sure you can save a reference trace to compare a live one against.
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
Visual or analytic ?
Both. For example, I made drivers for the V3500A power meter and SMIQ06B sig gens, and the attached is a comparison of multiple V3500A units using the SMIQ as the source.
For cable comparisons, I could do sweeps of all the cables with the SNA as both ends, and separate tests with the SMIQ as an external source to the SNA.
TestController will make charts and spreadsheets with the data.
Pretty sure you can save a reference trace to compare a live one against.
That would work for using the SNA by itself, but it would be fun to use other toys too. ;)
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
Do it >:D
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Also compare the prices to the Sucoflex 104 or higher, and they're definitely worth it. ;)
No arguments there ;D
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
Do it >:D
:-DD :-DD :-DD
I probably will. I've been procrastinating a driver for the Hioki IM35XX LCRs that I'll probably do first.
Do you have an SNA?
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I'm tempted to add support for the SNAs to TestController for sweep comparisons.
Do it >:D
:-DD :-DD :-DD
I probably will. I've been procrastinating a driver for the Hioki IM35XX LCRs that I'll probably do first.
Do you have an SNA?
Show AI the SNA programming guide and some TC code and set it loose. :P
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Show AI the SNA programming guide and some TC code and set it loose. :P
No need, I know how to do it. I've tried using AI in the past with it, and sometimes it helps a little. Mostly it screws up and guesses stupid shit and tries to force it to be something else. Some things AI is good at, and everything else makes shit take longer just correcting the AI slop.
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Do you have an SNA?
Not as of right now (but you never know >:D).
I have access to HPAK stuff and have the Agilent E7495A & the SV4401A here.
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Do you have an SNA?
Not as of right now (but you never know >:D).
I have access to HPAK stuff and have the Agilent E7495A & the SV4401A here.
Oh man, I'm looking forward to the points from that when you do get an SNA and blame me. :-DD
The driver I (might) make for the SNA series would only work for that series. Your HPAK stuff would need their own drivers (if somebody didn't already make one). I do have an SV4401A, but I don't think I'd make a driver for it, unless it's close enough to the SNA programming (assuming both use standard SCPI stuff). I haven't checked into either at all yet.
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Oh man, I'm looking forward to the points from that when you do get an SNA and blame me. :-DD
No blame will be assigned ;D. I've been on the fence for quite some time, but I keep buying used gear |O (just recently got a non-working 53220A to see if I can fix it).
SV4401A is just a toy, not even sure if it has ANY support for SCPI???
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Oh man, I'm looking forward to the points from that when you do get an SNA and blame me. :-DD
No blame will be assigned ;D. I've been on the fence for quite some time, but I keep buying used gear |O (just recently got a non-working 53220A to see if I can fix it).
I'm still gonna collect the points in the TEAS war. ;)
SV4401A is just a toy, not even sure if it has ANY support for SCPI???
Yeah, definitely a toy, but kinda fun. No idea if it has SCPI or what protocol it uses over USB. Not really exciting to explore with that one.
The UI in the SNA series needs some more development IMO, but it's generally awesome and fairly intuitive.
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I might have missed it, which SNA do you have?
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I got my feeBay Sucoflex 104 cables in today. One of them is definitely trash, the other not sure.
Here's the first one... There appears to be a defect at one end of the cable, and I'm guessing I had the wrong end in Port1 for the tests.
This one is getting returned.
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Here's the 2nd cable...
It was listed as N to N, but it's obviously N to SMA with an N adapter. Is the adapter why the DTF spike is wider?
With the adapter, it's not better than the M&P cables.
Should I keep this one or return it?
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I might have missed it, which SNA do you have?
SNA5002A with the 8.5GHz upgrade and the other options.
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I would return both. Your M&P are performing better.
That's why I don't buy used cables from eBay.
SNA5002A with the 8.5GHz upgrade and the other options.
Nice ;D
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I would return both. Your M&P are performing better.
That's why I don't buy used cables from eBay.
I mean, this one has that adapter on it, and that might be the reason it's performing poorly...and I only paid $22 total including shipping. I'm gonna test with another adapter. 🤔
ETA: The adapter is a Pomona 4297, which costs $37. Even if the cable is terrible (it isn't thaaat bad), it's probably worth it for the adapter if it isn't bad.
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This is that better Sucoflex cable with the Pomona SMA-N adapter on it. It's very sensitive to bends, but this is the best I got with it so far.
The other end also feels like SMA-N but is probably original to the cable (under heat shrink). Is that normal with these, or is this a weirder cable?
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The other end also feels like SMA-N but is probably original to the cable (under heat shrink). Is that normal with these, or is this a weirder cable?
The ones I've see have a direct N connector crimped to it, no adapters under the heatshrink.
What I don't like is the S11 plot. S21 will depend on the lenght of the cable. How long is it?
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The other end also feels like SMA-N but is probably original to the cable (under heat shrink). Is that normal with these, or is this a weirder cable?
The ones I've see have a direct N connector crimped to it, no adapters under the heatshrink.
What I don't like is the S11 plot. S21 will depend on the lenght of the cable. How long is it?
Yeah, the S11 looks weird for sure.
The DTF was accurate ~1.8m:
(https://www.eevblog.com/forum/testgear/cables-connectors-(nsmabnc)-adapters-with-measured-results-for-comparisons/?action=dlattach;attach=2815199;image)
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Just looked up the datasheet for Sucoflex 104 (I think that's what you have). It's supposed to be around 0.4 db/m @ 3GHz.
Maximum insertion loss @ 26.5GHz (for 1 meter cable) should be no more than 1.77db. That's with 3.5mm connectors, N will be a little worse.
So 1.3 db for 1.8m seems a little much. I think the adapters on the ends are screwing up the results.
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Yeah, I think so too. How can I remove the adapter from the equation? I have the auto fixture removal option, but I've never tried it and I don't know if it will be sufficient, or if it's even appropriate lol. SOLR is supposed to be better, isn't it?
I looked back on my M&P results, and they were significantly better. I forgot they were under 1dB. If the adapter is okay, I might keep it anyway, but I dunno. $22 shipped is cheap enough for the cable + adapter that it's not a big deal either way. I mean, that adapter has to be better than the free crap that came with my nanoVNA, right??
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I have the auto fixture removal option, but I've never tried it and I don't know if it will be sufficient, or if it's even appropriate lol. SOLR is supposed to be better, isn't it?
Not having hands on experience with the SNA line, I can't help there. In theory SOLR should do better.
If the adapter is okay, I might keep it anyway, but I dunno. $22 shipped is cheap enough for the cable + adapter that it's not a big deal either way. I mean, that adapter has to be better than the free crap that came with my nanoVNA, right??
The datasheet I was able to find for Pomona 4297 is a joke, the only "spec" they list is 0 - 12.5GHz frequency range.
For $22 I would personaly keep the cable, but I would either buy better adapters (which you probably want to have either way) or buy good connectors for that cable and re-crimp it.
Just my $.02 ;D
P.S. You will be paying WAAAY more than $22 for decent set of adapters :-DD
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Oh, I know, this shit gets expensive fast.
BTW- Aren't I doing this wrong anyway? SOLR, where R is Reciprocal for the "Unknown Thru" method. Searching says: "The Thru must be reciprocal (S21=S12)." But that's not the case here using an adapter.
Correct me if I'm wrong since I'm new AF to this stuff, but wouldn't I need to auto remove the adapter fixture, and then use two separate cal kits (N + SMA) to measure the cable correctly?
I'm guessing there's an easier way to do it. I dunno. 🤷
Either way, I think I'll keep the cable whether it's good or not. Eventually, hopefully, I'll be good enough to figure that out. :-DD
Attached is that same cable S11 with OSL correction, and nothing attached to the SMA end. I know, I know, I need to waste money on an SMA cal and load shit too.
Thanks,
Josh
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BTW- Aren't I doing this wrong anyway? SOLR, where R is Reciprocal for the "Unknown Thru" method. Searching says: "The Thru must be reciprocal (S21=S12)." But that's not the case here using an adapter.
Almost every passive network is reciprocal. Your cable+adapter certainly is.
If you have a high-quality, characterized and insertable Thru standard, you can do a regular SOLT calibration, of course.
Correct me if I'm wrong since I'm new AF to this stuff, but wouldn't I need to auto remove the adapter fixture, and then use two separate cal kits (N + SMA) to measure the cable correctly?
That’s correct. Attach the adapter to the VNA port (N-type) and calibrate at the SMA reference plane.
This effectively removes the adapter from the measurement.
[ Of course, this assumes the adapter is electrically stable; if you suspect it's faulty, the calibration may not be reliable. ]
De-embedding would be an alternative, but only if you already have the adapter's S-parameters.
I doubt AFR (Automatic Fixture Removal) will work here. It typically requires a fixture length of at least four wavelengths, and at your fmax of only 3 GHz, the adapter is simply too short.
If you want to isolate the cable, Time Gating out the connectors is straightforward, but you won't be able to isolate the connectors alone without including a few cm of the cable as well. Keep the resolution in mind: at only 3 GHz, even the shortest time-domain window is relatively wide.
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De-embedding would be an alternative, but only if you already have the adapter's S-parameters.
What parameters should I measure?
Is there a good tutorial somewhere to profile adapters and cal kits?
I have a shitty SMA cal kit that came with a nanoVNA, but if it's profiled well with the good N cal kit I have, then it should be usable, right?
It's clear I have a lot to learn.
Thanks,
Josh
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De-embedding would be an alternative, but only if you already have the adapter's S-parameters.
What parameters should I measure?
Simply measure the S-parameters of the adapter (S11, S21, S12, S22).
[ The catch, however, is that you need calibrated reference planes where the adapter can be mechanically inserted.
E.g. For an N to SMA adapter, the VNA needs one calibrated SMA port and one calibrated N port ]
Is there a good tutorial...
The 'VNA Bible' is the Handbook of Microwave Component Measurements: with Advanced VNA Techniques by Joel Dunsmore.
You'll find a lot of useful information on the web, too.
I have a shitty SMA cal kit that came with a nanoVNA, but if it's profiled well with the good N cal kit I have, then it should be usable, right?
How can you characterize the SMA kit if the calibrated VNA ports are N-ports where you cannot attach them?
You need a "golden standard", either a characterized SMA kit, or a characterized adapter.
Well, up to, say, 300 MHz, you can probably live with 'ideal' standards—meaning you treat them as ideal and just measure the RDC of the Load. But at 3 GHz, the parasitic effects and the electrical length of the standards are no longer negligible, making proper kit definitions essential.
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How can you characterize the SMA kit if the calibrated VNA ports are N-ports where you cannot attach them?
You need a "golden standard", either a characterized SMA kit, or a characterized adapter.
Well, up to, say, 300 MHz, you can probably live with 'ideal' standards—meaning you treat them as ideal and just measure the RDC of the Load. But at 3 GHz, the parasitic effects and the electrical length of the standards are no longer negligible, making proper kit definitions essential.
Thanks for all the info. I plan on getting a proper kit + adapters, probably from Roger. I do want to learn how to characterize stuff eventually.
Thanks,
Josh
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Nothing to add to what gf said already, it pretty much covers everything.
I don't have any SMA cal kits, I standardized on N connectors with all my stuff, otherwise I could have mailed you mine so you could check if what you have is good or not.
Thanks for all the info. I plan on getting a proper kit + adapters, probably from Roger. I do want to learn how to characterize stuff eventually.
Check out what MiniCircuits have in their catalog (not as a kit but as stand alone part numbers), then look around on ebay.
I have bought a few N loads, shorts, etc. from there. brand new, for a lot less than other places. And checked with calibrated VNA's they were all perfectly following the datasheet.
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If metrology-grade standards are not required, the Premium 12 GHz Calibration Kits from SDR-Kits offer a viable budget option.
While assembled using high-quality Rosenberger components, these kits cost only a fraction of official factory calibration kits.
https://www.sdr-kits.net/calibration-information-for-DG8SAQ-VNWA-3-3EC (https://www.sdr-kits.net/calibration-information-for-DG8SAQ-VNWA-3-3EC)
Unfortunately, they are currently listed as unavailable/sold out on their website.
EDIT: Even the Amphenol kits from SDR-Kits are likely better than NanoVNA bundled kits. While NanoVNA standards are completely uncharacterized No-Name parts, the Amphenol kits use genuine industrial-grade components and come with documented model coefficients (delay and fringe capacitance). Mechanical repeatability is likely better, too.
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Thanks! Those are some great prices. Looks like I'll get some kits from them too, eventually.
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This one is @mawyatt's fault. ;)
36" Gore Phaseflex N to N cable...from eBay. Of all the eBay cables, this one seems to be tougher in the sense that it maintains the results shown regardless of screwing around with the cable. I can push it up or down, left or right, slightly loosen the connector, and there's almost no difference if anything.
So, anyway... What do we think of this cable? Does it live up to the Gore name?
Thanks,
Josh
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This one is @mawyatt's fault. ;)
Glad I didn't get blamed for that one ;D
Much better. On S11 the worst is -33/-32db which is still quite good, but there's also a lot less variation with frequency (going from best case to worst case).
And a lot less loss too, .464db for 3ft that comes out to .155db/ft @ 3GHz, I can live with that.
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I retested the M&P Sahara 10 (S10, 3 meters) and Stealthflex 7 (SF7, 4 meters) cables for comparison with the Gore (36").
Am I correct that for a comparison between the 3, S11 looks best on the Gore cable, both in terms of level and shape?
S21 @ 3GHz:
Gore: -0.464dB
S10: -0.76dB
SF7: -1.541dB
Can we directly compare these, or not? If it's acceptable to multiply them all and pretend they're the same length, then wouldn't the S10 be the best for this measurement? Or is that now how we go about comparing S21 with different lengths?
Thanks,
Josh
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You are correct, S11 looks best on Gore cable.
You are also correct in assuming you can compare S21 between the cables.
Every manufacturers datasheet gives you attenuation per (however many) feet/meters for a particular frequency.
So @ 3GHz your Gore has -0.464db for 1M cable.
For 3M cable you just multipy -0.464 x 3 = -1.392db (which is more than S10 @ the same lenght).
Same for 4M: -0.464 x 4 = -1.856db (which in turn is more than SF7).
For VNA you don't need the lowest loss coax (within reason obviously), what you need is very good phase stability and a linear S11 (not sure how to phrase that one).
S11 of SF7 looks better than that of the S10, but I still don't like it :P
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Thanks, that's helpful.
S11 of SF7 looks better than that of the S10, but I still don't like it :P
That's what I expected you to say. ;) I will retry S10 again. It might be PEBKAC related. SF7 looked similar then I did something and it was flatter. :-DD
In any case, getting good results with that Gore cable took no effort. I think that's partially because it's much shorter and easier to setup without worrying about the extended length and whether I want to coil it or try and lay it out some way.
I did also get a lower quality Gore SMA cable (not Phaseflex) but it was not good. Rolling the dice on feeBay can be interesting.
Thanks,
Josh
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What's the deal with SRL? I want to try and setup the test the same way M&P probably did for the attached tested cables.
Thanks,
Josh
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In any case, getting good results with that Gore cable took no effort. I think that's partially because it's much shorter and easier to setup without worrying about the extended length and whether I want to coil it or try and lay it out some way.
That's the whole point of phase stable cables (which Gore & Junkosha are one of the few companies that make them), that they are very stable with flex & temperature.
So you don't have to "freeze" everything in time to perform measurements. But they cost arm & a d**k new :-DD
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What's the deal with SRL? I want to try and setup the test the same way M&P probably did for the attached tested cables.
I honestly have no idea what kind of VNA they used, but it definitely doesn't have enough points in the sweep.
But even in those tests you can see the impedance being very unstable.
Looking at the S10 test, if they had used as many points in the sweep as you did, they might have a similar result.
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Hmm, so it sounds like you're saying I should drop it down to 2 points, and then get a nice linear result? 🤔🤔🤣
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If you want to get results similar to what M&P have, yup. :-DD
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lol, I'm gonna do it just to try and match their test results.
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I dunno if I did the setup for this correctly, but...at least it looks cool. ;)
This is the Sahara 10. I should drop the points down to 51 to match M&P's lol.
Thanks,
Josh
ETA: Oh, I think this has to be wrong. It's a 3m cable. :palm: Eh, I'll figure out the right way eventually. :-DD
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Keep trying, you'll get it to look like M&P eventually :-DD :-DD :-DD
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What's the deal with SRL?
Researching the literature a bit, it seems that SRL measures the signal reflections caused by internal manufacturing inhomogeneities inside a cable, calculated as the deviation from the cable's own fitted characteristic impedance as a function of frequency. It is not the S11 you measure. It neither includes the connectors, nor reflections from the impedance mismatch between the cable's characteristic impedance and 50 Ohm.
Typically, it's measured for whole reels (say 100m). If the DUT is too short, SRL may not 'see' periodic manufacturing inhomogeneities introduced by the machine. While some mechanical vibrations cause variations in the centimeter range, slower cycle times can also introduce periods of several meters.
IEC TR 61156-1-5 defines the standardized mathematical techniques to calculate SRL from S-parameter data. I don't think that the Siglent VNA can calucate it directly, so you would need to export measured S-parameters and calculate offline.
The best freely available description I found was chapter 4.3 in the following paper (here it is called Fitted Returns Loss):
https://www.aesa-cortaillod.com/wp-content/uploads/2024/03/Paper-2020-IWCS-Procedures-to-overcome-spurious-effects-in-meas-of-RF-com-cables.pdf (https://www.aesa-cortaillod.com/wp-content/uploads/2024/03/Paper-2020-IWCS-Procedures-to-overcome-spurious-effects-in-meas-of-RF-com-cables.pdf)
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Typically, it's measured for whole reels (say 100m). If the DUT is too short, SRL may not 'see' periodic manufacturing inhomogeneities introduced by the machine. While some mechanical vibrations cause variations in the centimeter range, slower cycle times can also introduce periods of several meters.
Thanks. That's interesting, considering they charge extra to test the cable. 🤔
I asked them how they performed the test last year, and this was their response:
Hi Josh, the cable must be connected to the ports of a Vector Network Analyzer, the basic test measures the parameters S1-1 Impedance and Return loss.
Also, it ensures that the cable is working properly and the contacts with the connector are compliant (absence of standing waves).
On request, the parameters S1-2 (cable losses) can be measured only if this has a length > 5 meters for a 5 meter cable, 8-10 meters for cables
with a larger diameter.
From their answer, it sounds basic. Maybe something lost in translation?
Thanks,
Josh
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Keep trying, you'll get it to look like M&P eventually :-DD :-DD :-DD
I dropped it down to 51 points last night, and it's pretty ugly. ;) ...still the wrong length though. I need to learn the correct way to use a cable as a DUT and do the SOLR cal specifically for TDR.
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I dropped it down to 51 points last night, and it's pretty ugly. ;)
In order that you don't need to guess:
Lowpass TDR requires a harmonic frequency grid, i.e. f_start = step, and f_stop = N_points * step.
If non-harmonic frequency points are measured, the VNA would need to inter/extrapolate them for lowpass TDR, which is suboptimal.
[ DC unfortunately needs to extrapolated anyway as it can't be measured. ]
For good time resolution, use a large f_stop. The higher the frequency, the better the resolution: Δt = 1 / (2 × f_stop).
The frequency step (Δf) determines the maximum range of the time axis. A long cable requires a long time axis and therefore a small frequency step. For example, a 10 MHz step results in a time axis with a total duration of 1 / 10 MHz = 100 ns, which is typically displayed from -50 ns to +50 ns.
Keep in mind that the time axis resulting from the TDR (-> IFFT under the hood) is circular and wraps around. To avoid wrap-around (aliasing) of the data, make sure the time window is long enough for the DUT, and ideally even long enough to capture multiple reflections bouncing back and forth. If in doubt, it is always better to make the time axis longer than necessary by using a smaller frequency step.
Examples:
f_start = step = 10 MHz, N_points = 300, f_stop = 3 GHz (-> Δt = 167 ps, time axis = -50 ns ... +50 ns)
f_start = step = 1 MHz, N_points = 3000, f_stop = 3 GHz (-> Δt = 167 ps, time axis = -500 ns ... +500 ns)
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Because TEAS is real, and I'm an idiot, I bought a couple more Gore cables. First, here's a comparison of the original 36" cable with the new one also.
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Here's a 48 inch 3.5mm Gore cable using some crappy (free with nanoVNA) N to SMA adapters. I'm curious to see how this compares when I get some better adapters from @hendorog.
Thanks,
Josh
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Here's a 48 inch 3.5mm Gore cable using some crappy (free with nanoVNA) N to SMA adapters. I'm curious to see how this compares when I get some better adapters from @hendorog.
Thanks,
Josh
Even with crappy adapters the S11 still looks better than the M&P cables you were testing previously :-DD
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True, but they were attached during R calibration, so they shouldn't hurt it tooooo much, maybe? ;)
It will be interesting to compare it with some good adapters that will be properly calibrated out before R though...and also with the same good adapters calibrated the same way I did with the crappy ones...whenever I get them from across the globe.
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I got a 2nd Gore 3.5mm 48" cable in today. c1 is the original, and c2 is the new one.
Still with the crappy adapters and no torque wrench.
Playing with this crap has really made me look forward to getting better adapters and a torque wrench...and for that matter, a 3.5mm cal kit. Why is @hendorog on the other side of the planet?? ;)
I really want to see what these cables look like when I have that stuff. My cal kit only goes up to 4.5GHz, so I also want to see how they look up to 8.5GHz with the new kits.
Thanks,
Josh
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I'm messing around with the cal kits I got from @hendorog (see here (https://www.eevblog.com/forum/testgear/vna-lcr-calibration/msg6368793/#msg6368793)).
This looks pretty good, right?
It's a Gore Phaseflex 36in N to N cable. SNA cal'd with the N kit and torque wrench.
Thanks,
Josh
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Looks good to me ;D
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Thanks! I'm going to test out the 3.5mm cal sets, and then do some tests comparing the results with the same cable using the regular cal set and the LibreCAL.
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When comparing cables for using with a VNA, these are my thoughts:
With VNA cables the most important thing is how they react to movement.
Cable movement is almost unavoidable during a calibration and while connecting DUT's, at best it can be minimised. So the cables you want are the ones which change the least when moved.
Stability is more important than absolute performance. Anything can be measured but the stability makes the measurement repeatable.
That means the effect of the cable can be eliminated from the measurement of the DUT - and the same thing applies to adapters.
So it is worthwhile doing a test of the relative performance of the cable before and after it is moved and comparing the difference between cables.
That is what this procedure is all about: https://www.eevblog.com/forum/testgear/cables-and-connectors-for-vna-lt-3-ghz/msg2444583/#msg2444583 (https://www.eevblog.com/forum/testgear/cables-and-connectors-for-vna-lt-3-ghz/msg2444583/#msg2444583)
I think that will tell you which cable is the best for using on the VNA :)
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Also test the cable, then remove it and reinstall to see the variation.
Best
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Also test the cable, then remove it and reinstall to see the variation.
Best
Keeping everything clean (ports and cable ends) and properly torqued also matters.
A few days back for another post I dragged out my SVA1032X to show how to do Reference Offset to allow for pads/attenuator deduction so to keep levels correct and at ~1/2 sweep there was a blip on the trace from a -20dB TG signal. :-//
Just tightening the N connector properly made it disappear. :phew:
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I've done that with all my cables, and I'll do it again here. The cables I'm using for this are Gore cables, and there's almost no visible change messing with the cables compared to the others.
...and yes, I got some torque wrenches from Roger also. ;)