What does a VNA tell us about this antenna ?

[hendorog]

Now, a really interesting feature would be a "continuous valley" monitoring and linked markers for the desired performance.

For example, let's see I am adjusting this antenna. While I adjust the tuning controls the resonance frequency will change. Unfortunately the VNA function doesn't adjust the "valley" peak marker when it changes. So I must keep pressing peak->valley while I tune the antenna if I want the marker to be updated. It should "follow" the valley.

Linked markers: It would be great to specify something like: I'd like markers set to a certain RL or VSWR value. Again, updated if the antenna behavior changes because I am making adjustments.

I'm not sure what you mean when you say Linked Markers set to a certain RL/SWR? Do you mean something like a reference line, which is drawn across the screen at a particular level?

[tautech]

After that I have a couple more at least to write up here and one is a monster sized whip so that will need a fine day, something that's rare here ATM.

In preparation for this 3m long antenna let's check this ~5m N type M-F RG-213/U cable I have.
DTF set to 8m range and markers on the join to a 700mm cable and the RG-213 end afterwards.
RG-213/U cable specs:
https://www.rfparts.com/rg213-u.html

[borjam]

I'm not sure what you mean when you say Linked Markers set to a certain RL/SWR? Do you mean something like a reference line, which is drawn across the screen at a particular level?

Let's imagine I am tweaking an antenna. I am interested maybe not only on the resonance bandwidth, but also on the usable bandwidth. Let's see I want VSWR < 2:1. If I could set markers based on that value instead of frequency, it could display a table of markers with their frequency and the frequency difference between them.

In the case of my loop antenna it would create two markers and the delta frequency display would be really useful. In the past I had to adjust it by changing the shape of an internal coupling loop that affected both minimum VSWR and bandwidth a bit.

It could be a bit more useful now that you mention a reference line. It could show a table of "usable frequencies" by looking at the VSWR/RL line crossing the reference line.

And the real plus: imagine you are tweaking your antenna and your VNA is in the shack. You can access it from your phone via web, it could show a simple "tuning screen" with the information I am mentioning here.

[hendorog]

I'm not sure what you mean when you say Linked Markers set to a certain RL/SWR? Do you mean something like a reference line, which is drawn across the screen at a particular level?

Let's imagine I am tweaking an antenna. I am interested maybe not only on the resonance bandwidth, but also on the usable bandwidth. Let's see I want VSWR < 2:1. If I could set markers based on that value instead of frequency, it could display a table of markers with their frequency and the frequency difference between them.

In the case of my loop antenna it would create two markers and the delta frequency display would be really useful. In the past I had to adjust it by changing the shape of an internal coupling loop that affected both minimum VSWR and bandwidth a bit.

It could be a bit more useful now that you mention a reference line. It could show a table of "usable frequencies" by looking at the VSWR/RL line crossing the reference line.

And the real plus: imagine you are tweaking your antenna and your VNA is in the shack. You can access it from your phone via web, it could show a simple "tuning screen" with the information I am mentioning here.

Ahh right I get it. Actually I think I have seen something similar now you mention it.

[tautech]

I'm not sure what you mean when you say Linked Markers set to a certain RL/SWR? Do you mean something like a reference line, which is drawn across the screen at a particular level?

Let's imagine I am tweaking an antenna. I am interested maybe not only on the resonance bandwidth, but also on the usable bandwidth. Let's see I want VSWR < 2:1. If I could set markers based on that value instead of frequency, it could display a table of markers with their frequency and the frequency difference between them.

In the case of my loop antenna it would create two markers and the delta frequency display would be really useful. In the past I had to adjust it by changing the shape of an internal coupling loop that affected both minimum VSWR and bandwidth a bit.

It could be a bit more useful now that you mention a reference line. It could show a table of "usable frequencies" by looking at the VSWR/RL line crossing the reference line.

And the real plus: imagine you are tweaking your antenna and your VNA is in the shack. You can access it from your phone via web, it could show a simple "tuning screen" with the information I am mentioning here.

Ahh right I get it. Actually I think I have seen something similar now you mention it.

You can already do this of sorts.

For example in Log Mag (other modes too) adjust one trace in Amplitude to the Ref level you desire and place marker/s upon it where you desire. Then in the Trace menu enable a second trace and use that against the level set with the first trace.
Here we have trace 1 set to some Log Mag level and trace 2 the selected/active trace with markers un-coupled so to be able to move them independent of trace 1 markers.

Not all all hard to do, have a play borjam. 

[borjam]

You can already do this of sorts.

For example in Log Mag (other modes too) adjust one trace in Amplitude to the Ref level you desire and place marker/s upon it where you desire. Then in the Trace menu enable a second trace and use that against the level set with the first trace.
Here we have trace 1 set to some Log Mag level and trace 2 the selected/active trace with markers un-coupled so to be able to move them independent of trace 1 markers.

Not all all hard to do, have a play borjam. 

I'll check later at home. Anyway, a remote controlled VNA you can operate or at least watch from the discomfort of your tower using your phone can be a sort of a killer application for hams

Not "sort of", but actually doing it

[tautech]

Anyway, a remote controlled VNA you can operate or at least watch from the discomfort of your tower using your phone can be a sort of a killer application for hams

Not "sort of", but actually doing it

Well didn't I just demonstrate now you can set some arbitrary level with another trace then use another to do the tune ?

WRT SVA1015X remote control, behind the scenes one using the SVA's inbuilt webrowser is being prepared between NZ and Oregon as we speak !
Hopefully there'll be some evidence to study later.......

[borjam]

Well didn't I just demonstrate now you can set some arbitrary level with another trace then use another to do the tune ?

WRT SVA1015X remote control, behind the scenes one using the SVA's inbuilt webrowser is being prepared between NZ and Canada as we speak !
Hopefully there'll be some evidence to study later.......

Actually it would be possible to make a phone app to do something like this.

I'll play a bit more this evening and get back to you. Anyway, not criticizing, just making a suggestion.

[tautech]

Well didn't I just demonstrate now you can set some arbitrary level with another trace then use another to do the tune ?

WRT SVA1015X remote control, behind the scenes one using the SVA's inbuilt webrowser is being prepared between NZ and Canada as we speak !
Hopefully there'll be some evidence to study later.......

Actually it would be possible to make a phone app to do something like this.

Things already exist but I'll let those doing it explain later. 

[borjam]

I might have another interesting suggestion for automatic port extension correction, but I need to run some more tests.

(And given that I am far from a VNA guru, more a little grasshopper, the idea needs validation from more experienced folks here)

[tautech]

Yes, that is what I was referring to. It is a feature that should be requested.

Done !

Thanks borjam and Steve.

Useful indeed and a feature that certainly would've helped when I did final tuning of the J-Pole I made to resolve the proximity effects once it was installed.

Word back from the factory is Peak and Valley marker tracking is already on the 'to do' list.
No indication of when it might be added to firmware.....

[hendorog]

I have had the opportunity to play with an SVA which is sitting in Canada - from here in NZ. This was to see how usable the live web interface is over a WAN.

Latency was actually really good considering the distance, the ping is about 170ms. I was expecting it would be much worse than that.

The SVA was quite usable from a PC over VNC or the web interface which uses VNC internally.
The best result was using the RealVNC Google Chrome add-in with marker values updating up to 5 times per second.

The web interface, and any other VNC client I tried, including the RealVNC native client, was a bit slower. and any attempt to change settings like colour depth to improve the speed also made it slower.

I installed a VNC app on my phone. It wasn't as fast, and it had that age old problem of controlling a mouse cursor with a touch screen.
However it would have been perfect used readonly for monitoring a trace and/or marker values when tuning an antenna. Pinch to zoom the screen and the phone shows the full screen image landscape.

All in all it was surprisingly good over such a long distance.

[tautech]

Just had a quick play with the SVA1015X that hendorog connected to earlier.
Right now in NZ it's peak online time so the results with an iPad and the VNC app were a little disappointing due to latency of more than 1s which is not too bad at peak time considering it's in Oregon ! 
Still I made a couple of small adjustments to the setup and a marker just to prove to myself it works.

I installed the VNC Viewer from the Apple app store yet to get it working you need open a free account at realvnc.com Then it's just the matter of verifying yourself to them from emails and within the app and you're good to go.
The SVA1015X we've been able to connect too has been graciously made available to us on an open port by an EEVblog member.

While there I grabbed an iPad screenshot as proof of connection.
 

[tautech]

Yes, that is what I was referring to. It is a feature that should be requested.

Done !

Thanks borjam and Steve.

Useful indeed and a feature that certainly would've helped when I did final tuning of the J-Pole I made to resolve the proximity effects once it was installed.

Word back from the factory is Peak and Valley marker tracking is already on the 'to do' list.
No indication of when it might be added to firmware.....

Playing around with settings as a result of suggestions from borjam I've asked for another feature from the SVA team:
Limit lines.
SVA and SSA have them in SA mode so a Limit UI button is already on the front panel so I've asked if limits can be added into VNA mode.

We've got to keep the engineers busy don't we ? 

[hendorog]

Just had a quick play with the SVA1015X that hendorog connected to earlier.
Right now in NZ it's peak online time so the results with an iPad and the VNC app were a little disappointing due to latency of more than 1s.
Still I made a couple of small adjustments to the setup and a marker just to prove to myself it works.

Try it again now, it was on 751 points and taking a while to sweep. I changed it to 201 and its updating much faster.
I noticed it was on 201 points when I tested it.

I installed the VNC Viewer from the Apple app store yet to get it working you need open a free account at realvnc.com Then it's just the matter of verifying yourself to them from emails and within the app and you're good to go.

I was able to skip the RealVNC registration thing on the PC install. Not sure if that is the case with the iPad version though.

[borjam]

Playing around with settings as a result of suggestions from borjam I've asked for another feature from the SVA team:
Limit lines.
SVA and SSA have them in SA mode so a Limit UI button is already on the front panel so I've asked if limits can be added into VNA mode.

We've got to keep the engineers busy don't we ? 

As Groucho Marx would say, MORE WOOD!!

Yet another suggestion. It's confusing when you have more than one trace on screen but only one of the scales (the one for the currently selected graph).

What about adding scales with color matching the trace color? Or maybe at least balancing them left and right of the graph.

[tautech]

Yet another suggestion.

Keep em coming. 

It's confusing when you have more than one trace on screen but only one of the scales (the one for the currently selected graph).

Agreed but with the flag on the active trace visible on the left you do get used to it.

What about adding scales with color matching the trace color? Or maybe at least balancing them left and right of the graph.

Dunno how best to implement that and we best all have a bit of a chat and throw some ideas around.
Me, well it's getting late here and the brain fog is coming down. 

hendorog, we can chat about it tomorrow by mail. 

[tautech]

Next the 3m monster:
3x 450mm stainless radials

Small branding just above the radials identifies a NZ brand from which I've found a matching datasheet.
Datasheet attached below.

As it's big it will much lower frequency than those tested before therefore we limit the sweep to just 500 MHz.


Look at all those dips, we better look closer and find their frequencies.


OK so as I know were this antenna came from and have the repeater too I know the bands it operated in as 136 - 174 MHz so let's look closer at the best Log Mag dip and its SWR.
Here I've disconnected and set a second trace to a Ref level representing an acceptable SWR then switched back to trace 1 and reconnected.


Not ideal I know as RF connectors have a finite life and an important reason why I've asked Siglent to implement user Limits into VNA modes.

Finally a quick check with a Smith chart that raises some questions on the impedance match of this antenna.
I will add its location for testing was not optimum with several near field structures that would impact on its performance.

[tautech]

Now with a SVA1032X let's revisit the first subject I looked at, this 2.4 GHz WiFi antenna:



With the SVA1015X only 1.5 GHz sweep this was the Log Mag result:


Now with a 3.2 GHz sweep let's see how some of the markers placed align with the previous screenshot.
Markers 1 and 5 placed ~2.3 - 2.5 GHz




Discovered is another Wifi whip so that's the next subject with this new SVA1032X.

[tautech]

This time the Wifi antenna I mentioned above. It's a little longer than the white one tested previously and here I've added 100x averaging so to negate the operator proximity effects each time I adjust something on this SVA1032X.


Full 3.2 GHz sweep.

[RCinFLA]

Saying that anything below a given VSWR number is good can be misleading, other then lower VSWR is generally better.

A given VSWR number is a circle of a given radius around the center of Smith chart.  The number given in the mismatch loss equation is based on 10*Log10( 1-r^2) where 'r' is the circle radius ('rho').  This is only power transfer mismatch loss and does not take into account possible detuning effects on resonance of a transmitter output tank circuit or receiver input tank circuit with its optimum noise termination resistance.

A given VSWR can produce any impedance along the circle, from resistive, to inductive, to capacitive.  The given impedance can have a greater detrimental effect on the tank circuit tuning that results in more degradation in transmitter RF output power or receiver sensitivity then yielded by the mismatch loss equation alone. 

It can also cause instabilities in the transmitter PA or receiver LNA.  A 'load pull' test checks the stability when a given rho magnitude is rotated around all 360 degrees while checking for stability.  Putting a 100 ohm load on a 50 ohm line stretcher and moving length over half wave length range checks load pull for all impedances along 2:1 VSWR circle.

[E Kafeman]

 What does a VNA tell us about this antenna ?
It is a bit misleading label for this tread.
Antenna mounted directly at VNA is a very poor mounting place if it not is by purpose that VNA should be a part of the antenna measurement. Actual measurements curves shows dips at 400 and 1200 MHz. Antenna in it self is too short to provide resonances at these frequencies.
What is measured is to a degree the antenna and its nearfield such as the VNA. It is neither an antenna designed to be placed parallel and close to a big metallic surface.
Measurement setup is less optimal and VNA probably not correct calibrated.

Normally when measuring this type of antenna do we try to avoid that measurement cable is included in actual antenna measurement.
A free space with nothing that resonated near antenna and ferrite tubes around measurement cable is much the standard setup.
Connecting antenna directly at VNA and VNA is a bit hard to hide from actual measurement.

There is also some kind of problem with instrument calibration. For actual setup and type of antenna and frequency range, it is not even close to realistic impedance in last Smith Chart above. Guess that correct port forwarding not is performed.

I repeated a similar measurement below as a comparison. Measured a D-Link router antenna.



Connecting cable have several ferrite tubes and nearfield is not a part of the measurement. Note that Smith Chart is stable and not rotates a lot of turns. No low frequency anomalies are seen.
Similar result for most of my collection of old router antennas.

It is an interesting tool and price but very hard to judge what it is able to measure. Is it a network analyzer or single port analyzer (can it measure S12)?
Is it maybe a problem with its calibration? I have searched in the data sheet that could be found but could not find such information.

[tautech]

What does a VNA tell us about this antenna ?
It is a bit misleading label for this tread.

Please suggest a more suitable topic name.
Maybe one that has the VNA model # ?

Antenna mounted directly at VNA is a very poor mounting place if it not is by purpose that VNA should be a part of the antenna measurement. Actual measurements curves shows dips at 400 and 1200 MHz. Antenna in it self is too short to provide resonances at these frequencies.
What is measured is to a degree the antenna and its nearfield such as the VNA. It is neither an antenna designed to be placed parallel and close to a big metallic surface.
Measurement setup is less optimal and VNA probably not correct calibrated.

Yes all this is a problem for both the SMA WiFi whips I tested. On the last one I engaged averaging to somewhat negate operator proximity affects.

Normally when measuring this type of antenna do we try to avoid that measurement cable is included in actual antenna measurement.
A free space with nothing that resonated near antenna and ferrite tubes around measurement cable is much the standard setup.
Connecting antenna directly at VNA and VNA is a bit hard to hide from actual measurement.

What cable length in your experience might be suitable to mostly exclude nearfield influences ?
Just a few hundred mm or a meter or so ?

There is also some kind of problem with instrument calibration. For actual setup and type of antenna and frequency range, it is not even close to realistic impedance in last Smith Chart above. Guess that correct port forwarding not is performed.

Correct, no port extensions were used for the WiFi antennas so the N-SMA and SMA M-F adapters will impact some on results.

I repeated a similar measurement below as a comparison. Measured a D-Link router antenna.
(Attachment Link)
(Attachment Link)
Connecting cable have several ferrite tubes and nearfield is not a part of the measurement. Note that Smith Chart is stable and not rotates a lot of turns. No low frequency anomalies are seen.
Similar result for most of my collection of old router antennas.

Thanks for the lesson on how to do it !   

It is an interesting tool and price but very hard to judge what it is able to measure. Is it a network analyzer or single port analyzer (can it measure S12)?

No, it's a single port and through to the spectrum analyser input so only S11 and S21. Let's not forget the SVA models are spectrum analyser and VNA combo units. 

Is it maybe a problem with its calibration? I have searched in the data sheet that could be found but could not find such information.

Member hendorog and I have checked the Cal against a few SOL's that he has and the factory port Cal is pretty darn close.
Of the 2 units I have used in the antenna tests in this thread (SVA1015X and later SVA1032X) the SVA1032X is a spanking new unit that I already have a pre-public FW version that I have yet to install. I don't have the release notes for it but AFAIK it was to address some issues that Sharihar (TSP) found when he did a recent review.
https://www.youtube.com/watch?v=ToVJTKCyIU8&feature=youtu.be

Right how both my demo units are with hendorog for deeper comparisons against his 6 GHz HP and SH VNA's.

[borjam]

Antenna mounted directly at VNA is a very poor mounting place if it not is by purpose that VNA should be a part of the antenna measurement. Actual measurements curves shows dips at 400 and 1200 MHz. Antenna in it self is too short to provide resonances at these frequencies.
What is measured is to a degree the antenna and its nearfield such as the VNA. It is neither an antenna designed to be placed parallel and close to a big metallic surface.
Measurement setup is less optimal and VNA probably not correct calibrated.

Normally when measuring this type of antenna do we try to avoid that measurement cable is included in actual antenna measurement.
A free space with nothing that resonated near antenna and ferrite tubes around measurement cable is much the standard setup.
Connecting antenna directly at VNA and VNA is a bit hard to hide from actual measurement.

What cable length in your experience might be suitable to mostly exclude nearfield influences ?
Just a few hundred mm or a meter or so ?

The near field is determined by the wavelength. You can consider it a wavelength and, if you want to be safer, also include the transition zone. That would be two wavelengths.

https://en.wikipedia.org/wiki/Near_and_far_field

In order to check some WiFi/cellular antennas I used the actual cabinet of the equipment that would mount them, putting the miniVNA Tiny inside and using an adapter to connect the antenna.