Difference in SWR readings between nanoVNA and SWR meter

[vinlove]

OK, mate it is not a big deal for me. It is just a 30£ nanoVNA, how accurate it is, I was just testing out.

But RadioListener, you are the one who spray this forum with bullshit, not me.
Read your own posts, and think. You are not interested in giving out anything helpful for the OP. You are only into putting down others points like a piece of dirt.  You keep on going about the problems that doesn't exist.

I would take the screen shots, if I trusted what you were saying, but I no longer take you as a serious forum member. Sorry.
I don't want to go and do what you suggest to do, and get slagged off by you for the rest of this century, because that is what you get pleasure from.

You go and do what you want, and what you think is right. I am going to stop wasting time reading any more of your post from this moment.

[vk6zgo]

vinlove, this is not a specialist ham radio site.
I would suggest taking your original query to QRZ.com, where there are many people with experience of the type of antenna you are using.

[vinlove]

That is now what I am realising VK6ZGO.

I think that Radiolistenr guy is a just short wave listener who has not even touched real transceiver and transmitting antenna in all of his life.  He is just jealous and bitter at the real licensed Hams, because he failed to pass his HAM Radio Exam, it sounds like.  He says that his radios and antennas are registered to somewhere. I have never heard of that kind of rubbish in my life.

[radiolistener]

It is just a 30£ nanoVNA, how accurate it is, I was just testing out.

NanoVNA is much more accurate than any of your SWR meters, if you have any.
And you don't testing, you're trolling and insulting here. Nothing else.

But RadioListener, you are the one who spray this forum with bullshit, not me.

the bullshit here is just your posts. And all what you're doing here is just trolling.

People that needs help and answer won't write bullshit like that:

I don't have time to make screen shots of nanoVNA for this thread.

I don't need look at Smith Charts and make Screen Shots....

I would take the screen shots, if I trusted what you were saying, but I no longer take you as a serious forum member.

A lot of people asked you to provide measurements. But you still continue to ignore that and now you're started to insulting.

He says that his radios and antennas are registered to somewhere. I have never heard of that kind of rubbish in my life.

Where you from?

In my country the law requires government registration of transmitters and using unregistered transmitters is illegal even if you have license.

For example, this how it looks in the license:

[nali]

OK, mate it is not a big deal for me. It is just a 30£ nanoVNA, how accurate it is, I was just testing out.

But RadioListener, you are the one who spray this forum with bullshit, not me.
Read your own posts, and think. You are not interested in giving out anything helpful for the OP. You are only into putting down others points like a piece of dirt.  You keep on going about the problems that doesn't exist.

vinlove If you'd take a break from spitting your dummy out you might notice that it was OwO who actually brought up the subject of earthing & counterpoise. And from reading the content of his and your posts I'd say his knowledge on the subject is a good couple or orders of magnitude higher than your own.

You're being given advice but not listening as it's not what you want to hear, a trait shared by at least one other in this thread.

(and yes, I do hold an AR licence, have done for 25 years)

[m3vuv]

i think radiolisteners radios are maybe registered with chicken bands r us!

[Yansi]

It's almost surprising how ignorant some people can be.

[G7OVK]

Vinlove, I have read every comment in this thread by radiolistener, and everything he says is completely accurate. Your knowledge of the subject is clearly lacking, and you don't seem to be willing to accept what you're being told.

You could start by providing the screenshots/information requested so that we can investigate further. If you're not willing to, don't expect to have your question properly resolved.

[vk6zgo]

Vinlove, I have read every comment in this thread by radiolistener, and everything he says is completely accurate. Your knowledge of the subject is clearly lacking, and you don't seem to be willing to accept what you're being told.
You could start by providing the screenshots/information requested so that we can investigate further. If you're not willing to, don't expect to have your question properly resolved.

Much of what radiolistener says, is indeed correct, but he, like vinlove, has become so absorbed in his narrative that he tends to "draw the long bow".
For example, in dismissing the suggestion of interference from a  nearby high powered RF source, he says:-

For VNA there is no needs band pass filter, because it already measure SWR for specific frequency with very narrow bandwidth. NanoVNA uses PLL synthesizer for frequency sweep and SA602 mixers to shift frequency down and digitize it with 48 kHz ADC, further processing is performed in digital domain.

From my reading of that, he is asserting that having high selectivity following the mixer will guarantee narrow bandwidth at the device input.
This is, of course, not the case.
Historically Superherodyne receivers have had at least one tuned circuit before the mixer, or at the very least a bandpass filter.

With an untuned mixer &, effectively, a low IF, image interference is probable, as is intermodulation between the wanted frequency & even widely disparate frequency sources if they are strong enough.

SWR bridges are normally so insensitive that they are used with high enough power levels to make direct reading of external carriers highly unlikely.

Before the "chest beating" starts, I will state that I have been an Amateur Radio Operator since 1977.
In my working career, I spent 30 plus years working with TV & Radio Broadcasting, the latter both FM & AM (MF & HF), as well as Communications transmitters & associated equipment, so maybe my opinion might just, possibly, be worth considering.

My advice to the OP to take it to QRZ.com is based upon the fact that hams are a minority on this site, & QRZ has some people who are very experienced in the use of the type of antenna he has, & can give him advice which isn't associated with the ongoing "aggro" in this thread.
Whether he choses to take it, is up to vinlove. 

[m3vuv]

maybe this may help,found it on iogroups,sorted my issue out after pulling my hair out for almost 2 days! :Problem solved !

I'm running the new Nanovna-Q software from Nov. 26.
Before calibration I did the RESET, sure. The calibration resistors are OK, I have two, one that came with the NanoVna and one from MiniCircuits.

The RESET procedure was the problem:
 I did not realize that I also need to  SAVE to Cx right after Reset. Otherwise the data isn't really cleared and remains in the memory.
If I remember correctly in previous firmware versions the RESET automatically cleared the memory loction without having to save actively.

Whatsoever, now it works fine again.  Thanks for your inputs !

[radiolistener]

I did not realize that I also need to  SAVE to Cx right after Reset. Otherwise the data isn't really cleared and remains in the memory.

This is incorrect information. There is no need to save calibration right after CAL RESET. Save is not required at all for calibration. You can save calibration at any time if it needs, but you can use calibration with no save until power off.

Save is needed just to be able to recall calibration later, for example after power off.

Also, when you're doing clearconfig command there is needs power off before any save operation, otherwise save operation will restore old bad configuration and it will needs to repeat clearconfig again.

[OwO]

Historically Superherodyne receivers have had at least one tuned circuit before the mixer, or at the very least a bandpass filter.

With an untuned mixer &, effectively, a low IF, image interference is probable, as is intermodulation between the wanted frequency & even widely disparate frequency sources if they are strong enough.

SWR bridges are normally so insensitive that they are used with high enough power levels to make direct reading of external carriers highly unlikely.

This is all true, but in a VNA it's very easy to tell between external interferers and the true S11 response - the signal generator and the LO are phase coherent (when mixed down to DC with DSP you get a constant, unchanging vector) whereas any external interferers will have a random phase at any given time (unless they are somehow phase-locked to the same crystal as the LO). Hence the request for a smith chart which will very clearly tell you if you have an interferer problem or not. An interferer will show up as a "noisy" or "jagged" smith chart while physical devices will tend to have a "smooth" response provided you have enough resolution. This is also why I always say a cheap shitty VNA is better than a decent SNA because in a SNA (other than a few "special" models that are just a VNA with phase hidden from the user) you can not tell between an interferer and the device response and so are always "flying blind".

[m3vuv]

I did not realize that I also need to  SAVE to Cx right after Reset. Otherwise the data isn't really cleared and remains in the memory.

Thats total b.s!!you need to reset the call then save that slot before trying to write new cal data into it,otherwise it gets corupted!,dont take my word for it,try it!!

This is incorrect information. There is no need to save calibration right after CAL RESET. Save is not required at all for calibration. You can save calibration at any time if it needs, but you can use calibration with no save until power off.

Save is needed just to be able to recall calibration later, for example after power off.

Also, when you're doing clearconfig command there is needs power off before any save operation, otherwise save operation will restore old bad configuration and it will needs to repeat clearconfig again.

[radiolistener]

From my reading of that, he is asserting that having high selectivity following the mixer will guarantee narrow bandwidth at the device input.
This is, of course, not the case.
Historically Superherodyne receivers have had at least one tuned circuit before the mixer, or at the very least a bandpass filter.

With an untuned mixer &, effectively, a low IF, image interference is probable, as is intermodulation between the wanted frequency & even widely disparate frequency sources if they are strong enough.

There is no bandpass filter on the mixers input in the NanoVNA, but as OwO mentioned above, REF and LO sources are phase coherent. And external sources are not coherent with REF and LO, so it doesn't affect measurement much. Of course if it's power level is not enough to overload mixers input.

For example here is a small test.

I connected 145 MHz antenna to NanoVNA and take measurement:


After that I placed handheld radio near to antenna connected to NanoVNA and start transmission with about 5W power at 0.5 meter distance on 145.3 MHz and take second measurement on NanoVNA:


As you understand, there is very strong interference from 5W transmitter near the measured antenna. But do you see any significant difference in VNA measurement?

[radiolistener]

Thats total b.s!!you need to reset the call then save that slot before trying to write new cal data into it,otherwise it gets corupted!,dont take my word for it,try it!!

it gets more fun, especially when you wrote that you're using my firmware version.

I wrote you how to properly use it and now you wrote that this is bullshit... 

[m3vuv]

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An optional additional explanation is:

[Caaarlo]

I just did SWR reading on my HF antenna which is a EFLW with a balun.

At 7.15 Mhz, my SWR meter off ATU is 1:1.1 SWR.
On nanoVNA reading for the antenna at the same freq. is 1:2.87 SWR.

That I would say is, a huge difference.

Not sure which is right at this point and time.

Obviously one is wrong, or both wrong.
But it can't be both right?

I step in a bit late, but as far as I understand, you are using nanovna to measure the antenna directly, without ATU.
Well... have in mind that after that point, towards the TX, the ATU is transforming whatever impedance your antenna has, to a value close to 50 ohms (and this is what the TX actually sees)... that's the reason for the SWR meter built into the TX, to show an almost perfect SWR. But when measuring the antenna alone using nanovna, or any SWR meter, it will show the actual VSWR without the ATU impedance transformation.

If you bypass the ATU, or feed your antenna directly from the TX, then your SWR meter should read the actual SWR of your antenna, and it should be similar to the value shown by the nanovna (within a tolerance of 10% that analog meters usually have).

In short: SWR along the TX-ATU line can be completely different from the SWR along the ATU-Antenna line, especially when using high impedance antennas like yours.

[K0CRX]

I'm late to the show, too, but, I'll toss in my two cents.  I'm a very new user of a NanoVNA and I am seeing differences in readings like vinlove.

Using 160-meter off-center fed dipole -

Freq              3.5            3.7      4.0

NanoVNA     1.82          1.92     1.95     All instruments agree that the best match is at 3.3 mc
Autek  RF-1  H (>4:1)    H         H
MFJ 207        3+            3+       3+

Using 40-meter center fed dipole (might have a defective balun)-

Freq             7.0           7.2       7.3

NanoVNA     1.16          1.32    1.74
Aurek RF-1   3.6            3.3      3.9
MFJ 207       2.3            2.5      3+

The VNA has been properly calibrated as per instructions.  VNA measurements done using port CH0.  All units agree on the point of lowest SWR, but, do not agree on the indicated SWR.

Is it possible that we are using the wrong port?  Should the unused port be terminated?

[Yansi]

160m dipole for 3,5 meg? Wtf

3,5M is 80m band and the dipole size shall be 40m end to end.

[chris_leyson]

I tend to agree with radiolistener regarding SWR meter accuracy particularly where power level is concerned. You could build a 20dB or 30dB directional coupler using a pair of Ferroxcube 4C65 toroids for example and measure the voltage on the forward and reflected ports.
A long time ago I designed a 10kW 30dB directional coupler using 4C65 toroids and I think the core OD was about 35mm, I could be wrong about the OD maybe it was the next size up. Anyway, core area is determined by the lowest operating frequncy and peak flux density, 2MHz was the lowest operating frequency and I think the peak flux density was 30mT. I will have to run the numbers. Transformer directional couplers are not too difficult or expensive to build.

10:1 turns ratio will give you 20dB coupling and 32:1 will give you 30 dB coupling. See fig. 17 https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers
Also https://www.researchgate.net/publication/312570585_Design_and_development_of_a_dual_directional_coupler_with_transformers_for_HF_band_applications/link/5cf4a49ea6fdcc84750020fb/download

EDIT: I forgot to add, what accuracy does you SWR meter claim over a given range of source and load impedance and through power. It's hardly metrology by any standard just a ball park indicator.
Build a dummy load with a known SWR and then measure.

Just cos you got an ameteur license doesn't make you an RF engineer, you've got to step up to the mark, understand the measurements your instruments are making and why they might be wrong it's basic physics, just saying.

 

[metrologist]

At 7.15 Mhz, my SWR meter off ATU is 1:1.1 SWR.
On nanoVNA reading for the antenna at the same freq. is 1:2.87 SWR.

I was wondering, the ATU is measuring the tuned system. Is the VNA connected with the ATU not in line?

[radiolistener]

Is it possible that we are using the wrong port?  Should the unused port be terminated?

You're needs to use CH0 port of NanoVNA for VSWR measurements. The second port CH1 no needs to be terminated. Also, make sure you're performed calibration and it works properly before measurement.

Since you're using unbalanced antenna, you're measuring antenna with different ground configurations. Because unbalanced antenna using outer side of coax cable braid as a part of antenna, include metal case of your equipment. And even ground line of mains, if it has connection to the coax braid through metal case of your equipment.

In short, you're needs to take care to prevent common mode currents from antenna through your equipment, otherwise you will see measurements for different antenna configuration. In such case you will see different VSWR values, but all of them are correct. Just because unbalanced antenna (with no RF choke and balun) connected to different equipment are different antennas.

In order to test if you're measuring antenna instead of your equipment ground, just try to connect some long wire to the metal part of NanoVNA SMA connector (ground pin). With proper antenna it should not affect your measurement. But if you see different VSWR values with connected long wire, then there is a problem with your antenna. In such case you're needs to use RF choke, balun and ATU on the antenna side to eliminate such effect. Otherwise your antenna will be noisy and low efficient.

The most easy way to reduce such effect is to use RF choke from coax line, something like that:


This coil from coax line works as inductor for currents through outer side of coax braid, but it don't affect the signal inside coax cable.

How many turns is needed depends on the frequency. Lower frequency requires more inductance, so it needs more turns. For 3.5 MHz 10-15 turns should be enough.

This coil should be placed at distance about 1-2 meters from feeding point of antenna. Don't place it very close to antenna. For better performance you can place the same coil at the point where coax cable enters into your shack/building.


Be prepared that sensitivity of your antenna with RF choke will be reduced. Because you will see just your real antenna performance with no affect of parasitic ground. But at the same time you will see less noise from your home equipment and better antenna efficiency.

[chris_leyson]

I ran the numbers for a 30dB transformer coupler, N = 32 turns, Ferroxcube TX36/23/10 4C65 core,
Ae = 64mm^2 = 0.64cm^2, P = 10,000W, Erms = 707V, f = 2MHz. In cgs units and assuming a sinewave then Bpk(Gauss) = Erms x 1E8 / (4.44 * Ae(cm^2) * N * f(Hz)) = 388 Gauss or 38.8mT
The next size up TX58/41/18 has Ae = 152mm^2 = 1.52cm^2, Bpk = 164Gauss = 16.4mT.
I can't remember the exact core size but I do remember being a little aprehensive stuffing 10kW into it. The single or through winding is just the inner from some 50 Ohm coax with a copper tape shield grounded at one end. Somewhere I have a small 20dB coupler and will check it with a NanoVNA.

[g0fvt]

IMHO two of the contributors to this thread have been bang on the money. I believe the issue is common mode current/lack of a counterpoise whilst checking with the VNA.

[m3vuv]

ive had mfj 259 analysers give crazy reading on some antennas,i think its some sort of voodoo at work!