Author Topic: VNA recommendation  (Read 6485 times)

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Offline Nikos A.

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VNA recommendation
« on: January 28, 2022, 02:38:22 pm »
Hi guys,

We are looking to purchase a VNA for under 1000$.

Our target RF applications are under 3GHz.

Do you recommend any reliable VNA that you've used in the past?
 

Online Berni

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Re: VNA recommendation
« Reply #1 on: January 28, 2022, 03:47:05 pm »
I use the NanoVNA V2 for a lot of things.

It might look like a toy but it is a perfectly usable VNA. Might not quite have the stability, dynamic range or source flexibility as a real boatanchor VNA, but is also a lot cheaper and smaller than one. I have compared it to a real HP VNA at work and it measured up pretty well
 

Offline Grandchuck

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Re: VNA recommendation
« Reply #2 on: January 28, 2022, 04:06:10 pm »
https://www.tindie.com/products/hcxqsgroup/4-nanovna-v2-plus4/

I have this unit and it works well.  I have no way to compare it to a pro unit.
 

Offline 0culus

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Re: VNA recommendation
« Reply #3 on: January 28, 2022, 08:59:28 pm »
Just be aware that most of the cheaper VNAs are reflection/transmission only. They are not full two port VNAs (i.e. you need to manually reverse your DUT to measure S12/S22).
 
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Online joeqsmith

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Re: VNA recommendation
« Reply #4 on: January 29, 2022, 02:27:51 am »
Hi guys,

We are looking to purchase a VNA for under 1000$.

Our target RF applications are under 3GHz.

Do you recommend any reliable VNA that you've used in the past?

Missing one or two zeros?   :-DD   

Even in the used market, I'm afraid you're not going to find much at that price.   If you want to try one of the low cost VNAs, which I highly recommend for anyone just starting out, just keep in mind all the limitations.  There's no input attenuators, output power setting, square wave drive, poor dynamic range .... But they are very inexpensive and a lot of fun.   They are very low risk IMO.   

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We can add an external transfer relay, step attenuators, bias Ts and even a PC to the mix.         
« Last Edit: January 29, 2022, 03:27:08 pm by joeqsmith »
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA, V2+4 and LiteVNA may be found here:
https://github.com/joeqsmith
 
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Online Berni

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Re: VNA recommendation
« Reply #5 on: January 29, 2022, 11:56:09 am »
Just be aware that most of the cheaper VNAs are reflection/transmission only. They are not full two port VNAs (i.e. you need to manually reverse your DUT to measure S12/S22).

Yep this is usually the case, but then again how often does one even need to measure the reverse transmission parameter? Most of the time just a single port is used (antennas, input matching, parasitic mesurements etc..) and most of the two port stuff you want to measure are things that don't care about direction (like cables) or things that are designed to work in one direction (like amplifiers or some filters)

You can still flip the device around if needed. It's not like the phase repeatability matters that much with a 100$ VNA nor do you need fancy expensive connectors that you might be scared of wearing out. Most of the time you won't be using a proper calibrated (with correction data) open short load standard anyway since such a standard can cost 10 times as much as such a cheap VNA.

You can do a lot with these tiny cheap VNAs, as long as you are aware of its limitations.
 

Offline G0HZU

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Re: VNA recommendation
« Reply #6 on: January 29, 2022, 03:42:52 pm »
With a budget of just $1000 you might be able to buy an old 3GHz HP 8753A TR VNA. If you could stretch to $1500 you might be able to buy something like a full two port 8753C with unknown history. Reliability would always be an issue with something this old. It might already be faulty on the day it gets delivered or it might only work for a month or it might work for 5 years without any problems.

A lot depends on what you want to do with the VNA and what performance level is acceptable. The V2 nanovnas look to be quite capable but the big disappointment here is that there are no decent reviews online for these low cost VNAs. There's no shortage of enthusiastic reviewers but they don't really test the limits of the VNA.
 

Offline 0culus

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Re: VNA recommendation
« Reply #7 on: January 29, 2022, 04:06:54 pm »
Just be aware that most of the cheaper VNAs are reflection/transmission only. They are not full two port VNAs (i.e. you need to manually reverse your DUT to measure S12/S22).

Yep this is usually the case, but then again how often does one even need to measure the reverse transmission parameter? Most of the time just a single port is used (antennas, input matching, parasitic mesurements etc..) and most of the two port stuff you want to measure are things that don't care about direction (like cables) or things that are designed to work in one direction (like amplifiers or some filters)

You can still flip the device around if needed. It's not like the phase repeatability matters that much with a 100$ VNA nor do you need fancy expensive connectors that you might be scared of wearing out. Most of the time you won't be using a proper calibrated (with correction data) open short load standard anyway since such a standard can cost 10 times as much as such a cheap VNA.

You can do a lot with these tiny cheap VNAs, as long as you are aware of its limitations.

The OP sounds like a business possibly, and they didn't elaborate further so we don't know what their requirements are.

joeqsmith above pointed out another serious limitation of the cheap VNAs: square wave drive. This may work fine for most passive devices, but it can cause issues with active device characterization. Plus, if a DUT isn't reciprocal (e.g. a limiter), you may want to know what it looks like from both ends.

"Real" VNAs are more than just being able to do full 2 port S parameters, there's also more control over the stimulus (drive level, step attenuators, DC bias tee for powering amplifiers under test), better repeatability, etc. If a TR test set is sufficient for the OP's needs, that's fine, but in absence of more info about what THEY need out of their VNA, we can only brain dump....
 
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Online Bud

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Re: VNA recommendation
« Reply #8 on: January 29, 2022, 04:08:58 pm »
Toys are just that - toys. None of those toy VNA creators bothered to pull an old HP VNA manual to see what should be involved in VNA specification and characterization.

@OP: as was said, a used 8753 series HP VNA would be your best bet "if" you are serious and do not mind boat anchor device size and weight. If you just want to learn and not measure, go with watever handheld gadget from Aliexpress.
Facebook-free life and Rigol-free shack.
 

Online joeqsmith

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Re: VNA recommendation
« Reply #9 on: January 29, 2022, 06:29:38 pm »
There's no shortage of enthusiastic reviewers but they don't really test the limits of the VNA.

You can always show us but as you stated, I think I already know how this story ends.  :-DD
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA, V2+4 and LiteVNA may be found here:
https://github.com/joeqsmith
 

Offline G0HZU

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Re: VNA recommendation
« Reply #10 on: January 29, 2022, 06:41:01 pm »
There's no shortage of enthusiastic reviewers but they don't really test the limits of the VNA.

You can always show us but as you stated, I think I already know how this story ends.  :-DD

Your attempt to demonstrate finger torque vs a torque tool was probably your funniest fail for me. Maybe you should stick to blowing things up :)
 

Offline coppercone2

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Re: VNA recommendation
« Reply #11 on: January 29, 2022, 07:07:11 pm »
 

Online joeqsmith

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Re: VNA recommendation
« Reply #12 on: January 29, 2022, 07:15:42 pm »
Your attempt to demonstrate finger torque vs a torque tool was probably your funniest fail for me. Maybe you should stick to blowing things up :)
Its out of character for you but I'm glad to hear you found some humor.

This one using a much larger wrench to snap a few was pretty good.


But I had fun playing with the printed wrenches as well.
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA, V2+4 and LiteVNA may be found here:
https://github.com/joeqsmith
 
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Offline Kim Christensen

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Re: VNA recommendation
« Reply #13 on: January 29, 2022, 07:39:44 pm »
Be aware that if you go for a 8753C, that if you want a full S-parameter test setup, it's a separate module. ( 85046A for up to 3 Ghz or 85047A for 6Ghz )
An upgrade from the C version is the 8753ES but you won't find a working one for under $1000. ( keep a keen eye on the options installed! )
« Last Edit: January 29, 2022, 07:42:09 pm by Kim Christensen »
 

Offline G0HZU

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Re: VNA recommendation
« Reply #14 on: January 29, 2022, 08:49:24 pm »
Normally I'd suggest trying to buy an old ex-rental analyser from a rental company. Every so often they sell off the older stock at low prices. The other option would be to try and attend a few local auctions of test gear. I've bought some nice test gear using these methods at quite low prices. However, I'm not sure how realistic this would be in Cyprus.

If I wanted to buy a decent VNA on a low(ish) budget I'd try and buy a HP 8753D but this is likely to cost $2500. If I only had less than $1000 to spend I'd probably buy a 3GHz nanovna V2 for <$200 and then start saving for the HP 8753D.

 

Offline rfclown

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Re: VNA recommendation
« Reply #15 on: January 29, 2022, 10:44:39 pm »
I can't recommend anything under $1000. I use (and recommend) used HP8753s, but they aren't that cheap, and they are huge. A 3.5mm cal kit in good condition might cost $1000 used. I started with a 8753B that I paid $1800 for without a test set (I used couplers). Then I bought a test set. Sold B and upgraded to 8753C... etc... now I have a 8753D with test set. All bought on eBay, but nothing was cheap. But these are solid VNAs. They are what I used at my job before being laid off in 2009, and what I decided to buy when I started contracting. I have a nano S-A-A V2 that I got out of curiosity, but I don't use it since I have my HPs. It is amazing for what it is, but it's not the same. In 2018 I bought a Copper Mountain R60 (single port USB VNA) for a company I was working for to test antenna assemblies (TDA function came with it), but I think we paid $3k for that. Seems like there's the $100 nano kind of thing, or the several thousand dollar thing. Not really anything in between.
 

Offline 3isenhorn

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Re: VNA recommendation
« Reply #16 on: January 30, 2022, 09:53:51 am »
Hi,

Depending on your use case and budget, you might have to consider alternatives.
Do you really need the Vector capability?  Do you need the full two-port capability?
Maybe a spectrum analyser with tracking generator is the right choice? Maybe some of these devices are even already available?

In general, I think it's hard to get a complete VNA setup for under $1000, as that would include a CalKit for me.


 

Offline cdev

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Re: VNA recommendation
« Reply #17 on: January 30, 2022, 09:32:26 pm »
I have a nanovna2 which I spent less than $100 for, on tindle, total. I also have a nice aftermarket case for it. It can work up to 4.4 GHz with some peaks between 3 and 4.4 Ghz. Up to 3 Ghz is what its rated for. I also have a cal kit for it. Which are simple SMA components.

It gets a lot of use. For the stuff I do it works great.
« Last Edit: January 30, 2022, 09:35:11 pm by cdev »
"What the large print giveth, the small print taketh away."
 

Offline chrisl

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Re: VNA recommendation
« Reply #18 on: January 31, 2022, 01:19:07 am »
Look for an used Agilent 8714ES.  Will cost more than $1000 but you can find a deal time to time that will be near $1k.
 

Offline TheSteve

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Re: VNA recommendation
« Reply #19 on: January 31, 2022, 01:33:45 am »
Look for an used Agilent 8714ES.  Will cost more than $1000 but you can find a deal time to time that will be near $1k.

This is an excellent choice. You can easily do a color LCD upgrade or connect an external LCD monitor if the green screen bothers you. I have seen this go for great prices over the years. Very under appreciated.
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Offline tautech

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Re: VNA recommendation
« Reply #20 on: January 31, 2022, 08:06:55 am »
Hi guys,

We are looking to purchase a VNA for under 1000$.

Our target RF applications are under 3GHz.

Do you recommend any reliable VNA that you've used in the past?
~60% over your budget:
SSA3021X+ and hack it to a SVA1032X ...... a 3.2 GHz SA and VNA.
Avid Rabid Hobbyist
Can help with advice on Siglent equipment when time allows.
 
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Offline Nikos A.

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Re: VNA recommendation
« Reply #21 on: January 31, 2022, 09:08:14 am »
Thank you for your replies guys!! Really appreciate it!!

A friend of mine measured the S11 parameter of a 6dBi antenna manufactured by Kerlink using the NanoVNA SAA-2N V2.2
https://www.amazon.de/Converter-50KHz-3GHz-Measuring-Parameters-Standwave/dp/B099S5NNMN

For this test, the ACCIOT-KAN01 (868MHz) antenna was used. This antenna is used for the LoRa gateways in the EU. This is the datasheet.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fcdn.shopify.com%2Fs%2Ffiles%2F1%2F0447%2F5633%2F6807%2Ffiles%2FDatasheet-6dbi-ACCIOT-KAN01-ACCIOT-KAN02-v1-0tmzmxMR5JTmBJ.pdf%3Fv%3D1615569419&clen=773192&chunk=true



This test shows that the antenna is more efficient on 853MHz instead of 868MHz.

Probably the antenna is not well designed by the manufacturer - hard to believe since this is a well-established and known manufacturer.
Could this low-cost VNA make such inaccurate measurements?
Also, the state of calibration of this VNA is unknown - I do not know if they even calibrate such a low-budget equipment


 

Online Berni

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Re: VNA recommendation
« Reply #22 on: January 31, 2022, 11:09:02 am »
The return loss of 15dB is a VSWR of 1.4 while a 10dB return loss is a VSWR of 1.9 so it is a reasonably good antenna at both of those frequencies.

Antennas are also affected by proximity to other things, so the actual optimal frequency can shift about somewhat. So how you place your antenna might affect your mesurement and once the antenna is installed it might have a different response again. For that reason you typically don't aim to tune an antenna for a super super good return loss, that tune will be thrown off by antenna installation anyway, so you often don't really aim for any VSWR bellow 1.5, anything under 2 is also pretty decent, above about 3 is a bad antenna.

Tho it depends on application, a little wifi module won't care about a little reflected power. But a 100kW radio transmitter feeding a giant antenna on top of a radio mast will end up having many kW bounced back if the VSWR is not really really good. Since it's on top of a giant mast you don't have to worry about things getting close to it to detune it and you can afford to have some extra tuning elements that get adjusted for best possible VSWR

So for just a LORA antenna the accuracy of a NanoVNA is plenty good.

EDIT:
Also once you have a VNA you can easily DIY a lot of antenna types from just wire and RF connectors you have laying around. That way you can make an antenna that is built to your needs and tune it to be as precise as you want it to be. Lots of antenna designs out there with there own pros and cons (some are small, some are wideband, some are narrowband, some are insensitive to detuning, some are very directional, some are very omnidirectional.. etc)
« Last Edit: January 31, 2022, 11:16:13 am by Berni »
 
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Offline cdev

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Re: VNA recommendation
« Reply #23 on: January 31, 2022, 05:40:54 pm »
All antennas that are supposed to be soldered permanently to pieces of electronics are specified under certain conditions, say what size ground plane they have. Measurements of such antennas are useless in other contexts.

For example, a ceramic GPS antenna produced by Taoglas may be intended for mounting in the center of a piece of PCB and resonate at the right frequency when it is. But if its mounted at the end of a device where it doesn't have a ground plane not only wont it resonate at the right frequency, which means that it wont get the polarization right as its a highly optimized design that shrinks the size of a patch antenna and depends on all sorts of factors relating to whats around it. Off tune it will also likely function worse than a (spiral) piece of wire cut to the correct frequency and diameter and also wont have the proper polarization meaning rejection of signals that are not GPS.  its likely.

Making the significant extra expenditure on a "real" GPS antenna useless. Installed badly, you fancy, small ceramic antenna may be less than useless. Buying a commercial antenna doesn't guarantee you anything except spending the money. Understand the users responsibility is to provide the antenna with the right environment so it can work. Make sure you interact in a meaningful way with the manufacturer to get the support you are paying for by buying their product. Thats absolutely essential if ceramic materials are involved. Because that tells you its a system, with missing parts, besides the antenna itself.

A good VNA can give you much of the information you will need to do this properly but not all of it. The other half is YOU. You need some knowledge of how RF behaves and some common sense, and some trial and error to get it consistently right. As you see, now you can spend a lot less. But if you get a functional VNA that is just the beginning of a learning journey. Its going to be a fairly similar journey no matter how much you spend on a VNA, if it is a VNA. Best that it be an inexpensive journey if you are a beginner. Maybe later on when you really NEED a better one for some specific reason and your expenditure is likely to be a needed one then spend more on one then.

A plastic case may be better in terms of accuracy.

The best advice I can give you is call them (the antenna manufacturer) on the phone and have a discussion with your manufacturers support person, and if you can send them a picture of your proposed usage of their antenna in situ, as it were.  I would ask them what their antenna gives you that a monopole doesnt. There is a good chance that its simply a size reduction. It may have lower gain than a monopole. 

Ask them to sell you their antenna. (Justify the expense to you).  Just because a family of devices claims long range, doesn't mean that their devices actually possess the ability to traverse that long range.  Given the nature of VHF and UHF, it may actually be impossible for the signals to go very far if the devices at the two ends of the link are no more than a meter or two above the ground.

Speak to them. Thats almost a must-do if real money is about to be spent. Better safe than sorry.
« Last Edit: January 31, 2022, 06:11:02 pm by cdev »
"What the large print giveth, the small print taketh away."
 
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Offline Joel_Dunsmore

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Re: VNA recommendation
« Reply #24 on: January 31, 2022, 08:46:16 pm »
Thank you for your replies guys!! Really appreciate it!!

A friend of mine measured the S11 parameter of a 6dBi antenna manufactured by Kerlink using the NanoVNA SAA-2N V2.2
https://www.amazon.de/Converter-50KHz-3GHz-Measuring-Parameters-Standwave/dp/B099S5NNMN


Probably the antenna is not well designed by the manufacturer - hard to believe since this is a well-established and known manufacturer.
Could this low-cost VNA make such inaccurate measurements?
Also, the state of calibration of this VNA is unknown - I do not know if they even calibrate such a low-budget equipment
A couple things about measuring dips in return loss of antennas:
The dip shows the point where the antenna impedance matches the calibration load impedance (plus any cable flexure changes) of the VNA.  I had one customer swear the crystal oscillators in his 8714's were drifting because the dip in his antenna return loss was moving in freq. We had to ship an SA to him so he could measure each one and see they were all exactly in spec (they never really drift). The cause was a poor load, a drifty cable, and the fact that the return loss dip does NOT say where the antenna is tuned in frequency, only where it is tuned to match the reflection impedance. To test the real frequency you need to do an OTA transmission test.

And, as has been mentioned, the ground plane configuration makes an absolutely huge difference in how the impedance appears at the VNA.

oh: and be sure to discharge (ground) your feedline from the antenna before connecting to the VNA; it's very easy to build up a large charge.

Oh: and if you are near an airport or the coast, watch out that the radar doesn't sweep by your antenna and blow up the front end of the VNA (another long story about the French company which did that).
 
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