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T-Check with LabView NanoVNA


John Galbreath 2021/08/20 21:31

Is it necessary to have a transfer relay to perform a T-Check with LabView/NanoVNA ?  I did not get the prompt to install the T-check adapter as described on page 112 of the manual.  I have an AURSINC clone and this may create havoc.

Joe Smith 2021/08/21 03:13

In general I have seen posts, typically from the radio hobbyist, that claim you do not need a transfer relay to perform a T-Check.

As for my software, I assume that the user knows what they are doing and typically won't impose any limits.  Once again, I have no crystal ball to see what you are doing and you provide no details to allow anyone to replicate it. I assume the problem is between the PC and chair.  Start by checking there.  Of course, there are videos demonstrating the T-Checks use if you would like to learn more about it.

Joe Smith 2021/08/22 08:25

Looking at my source, even without a VNA attached, the software should still display the prompt.   Now why anyone would ever do that, I am not sure but it gets back to what I mentioned.  As a general rule, I don't normally limit what you do with the software.

Of course, its not magic and the manual is clear that you have to actually press the T-Check button.
" Next select the T-Check button. You will be prompted to install the T-Check adapter. "

There may have been some question as what a "button" is or where is is located.  Still, you have watched the videos and this seemed clear enough but maybe not:
https://youtu.be/XaYBpPCo1qk?t=2188

I'm staying with the problem being between the keyboard and chair unless you provide details that show otherwise.

John Galbreath 2021/08/24 09:27

Yes, the situation was caused by operator error.

I noticed that on the YouTube tutorial that you recommended an Omron RF relay as a transfer relay.  I doubt my ability to design a gadget to receive USB command to change transfer relay state and send relay status back via USB to the PC.  Does your LabView program allow for manual transfer relay operation, as I found a Bird DPDT manual RF switch with N connectors which is low SWR, low insertion loss and high in isolation.  Could the program prompt me to manually change the Bird RF switch and click "OK" when I change it ?

Joe Smith 2021/08/24 11:04

On Wed, Aug 25, 2021 at 12:27 AM, John Galbreath wrote:

>
> Yes, the situation was caused by operator error.

Good yo know you sorted it out.  Pressing the button is pretty important.

>
> I noticed that on the YouTube tutorial that you recommended an Omron RF
> relay as a transfer relay.  I doubt my ability to design a gadget to
> receive USB command to change transfer relay state and send relay status
> back via USB to the PC.  Does your LabView program allow for manual
> transfer relay operation, as I found a Bird DPDT manual RF switch with N
> connectors which is low SWR, low insertion loss and high in isolation. 
> Could the program prompt me to manually change the Bird RF switch and
> click "OK" when I change it ?

I doubt you will find anywhere that I recommended an Omron relay as the isolation was very poor.  What the manual does state is:
"The left most relay is an old Transco device. It was designed for operation to 18GHz and is well suited for this task."   Transco, Omron, what's the difference...

For the control, there is hardly anything to design.  Again, referring to the manual:  "It uses a common USB – TTL adapter from FTDI."  and for the beginner, there is even a schematic for a small DC-DC converter that I put together from the junk box to drive it.   Again, its not something I would recommend anyone construct but it's there for a reference.

I highly recommend you clean out your ears and listen very carefully to the following video.
https://youtu.be/XaYBpPCo1qk?t=1928

Of course, you may have watched the first video but if you pay close attention and listen, I think you will find I again talk about the poor performance, not just once.
https://youtu.be/GJNMnq8eD0E?list=PLZSS2ajxhiQD2gftdurGQoyGpUM_HobNI&t=728
https://youtu.be/GJNMnq8eD0E?list=PLZSS2ajxhiQD2gftdurGQoyGpUM_HobNI&t=2051

It hardly seems like a recommendation of any sorts but feel free to point out where I contradict any of this.

These videos are long, boring and data heavy.  They are not meant to be entertaining but rather explain the basics to the beginning EE.  I certainly understand that with today's culture where everyone is an expert after watching 5 minutes of video, that actually sitting down and trying to learn anything seems foreign for many of us.  It's easier to just post on the forums.  So I certainly understand but I think you would be far better served by actually spending the time watching and listening rather than posting.

John Galbreath 2021/08/24 11:08

OK, I don't like the Transco or Omron relays either.  What is your opinion regarding the suitability of the manual Bird RF switch ?

Jim Lux 2021/08/24 12:21

On 8/24/21 9:27 AM, John Galbreath via groups.io wrote:
> Yes, the situation was caused by operator error.
>
> I noticed that on the YouTube tutorial that you recommended an Omron
> RF relay as a transfer relay.  I doubt my ability to design a gadget
> to receive USB command to change transfer relay state and send relay
> status back via USB to the PC.

Probably not get status back (and a lot of surplus transfer relays don't
have status contacts anyway), but there's tons of USB relay boards on
Amazon. You'll need a two channel one (typically a transfer switch has
two coils).

Make sure you get one that has a published interface - some come only
with a windows exe, and that's useless.

Here's a slightly more upscale vendor, with which I've had decent luck:
https://www.phidgets.com/?tier=1&catid=2&pcid=1

I've bought a variety of USB controlled widgets from a multitude of
Chinese vendors, some work, some don't - there's some learning curve and
research required. Some work with Windows, but not with Mac or Linux/RPi.

You might also try places like adafruit.com.






Jim Lux 2021/08/24 12:35

On 8/24/21 11:08 AM, John Galbreath via groups.io wrote:
> OK, I don't like the Transco or Omron relays either.  What is your
> opinion regarding the suitability of the manual Bird RF switch ?
> _._,_._,_
> ------------------------------------------------------------------------

Automation vs manual? Automation reduces a source of mistakes. You solve
the problem once, and never have to worry about it again.

My rule of thumb at home is:

Do it by hand up to 3 times, after that, figure out how to automate it.

at work it's:

Do it by hand once, so you know what steps to automate. Then automate.

That's because oopsies at work cost money out of the budget to redo the
test (or prove that you didn't break something).

If you can get a transfer switch cheaply, and you want to make full 4
parameter measurements on a regular basis, then it's probably worthwhile.

Max Gain Systems (https://mgs4u.com) for instance has a variety of
transfer switches for $40

https://mgs4u.com/product/rly-sma-64/

You'll cobble together that, a 24V power supply, some short coax jumpers
(preferably hardline), and some sort of USB interface (another $20-30) -
for <$100, you'll be set pretty much forever.

Joe Smith 2021/08/24 15:22

>... I found a Bird DPDT manual RF switch with N connectors which is low SWR...
>OK, I don't like the Transco or Omron relays either.  What is your opinion regarding the suitability of the manual Bird RF switch ?

As much as you seem to believe I have a crystal ball,  I would have no way to know what part number you are looking at, how you intend to connect it or what your requirements are.   If it really is a DPDT, I assume it has six N connectors.  How do you even plan to connect it in the RF path?   Why would you ever consider something like this over using an actual transfer relay?    You can find the old Transco relays but anything used is going to be a total gamble.  I wouldn't bother.  You could buy a new one but expect $500 on up.  Even if you added one, you are still limited by the VNAs hardware.

While the software allows you to manually control the transfer relay, it expects it to be under software control when it's being used.  I have no plans to support a manual method.

Depending on your wants/needs, you could wait and see what OWO brings to the table next.  Estimated price is around the cost of a transfer relay.  May be other benefits as well.  We have to wait and see.

I've seen some pretty odd posts when it comes to making full 2-port measurements.  The best so far was one of the radio hobbyist suggesting to use two VNAs.  You can't make that stuff up.

Jim Lux 2021/08/24 16:27

On 8/24/21 3:22 PM, Joe Smith via groups.io wrote:
> >... I found a Bird DPDT manual RF switch with N connectors which is
> low SWR...
> >OK, I don't like the Transco or Omron relays either.  What is your
> opinion regarding the suitability of the manual Bird RF switch ?
>
> As much as you seem to believe I have a crystal ball,  I would have no
> way to know what part number you are looking at, how you intend to
> connect it or what your requirements are.   If it really is a DPDT, I
> assume it has six N connectors.  How do you even plan to connect it in
> the RF path?   Why would you ever consider something like this over
> using an actual transfer relay?    You can find the old Transco relays
> but anything used is going to be a total gamble.  I wouldn't bother. 
> You could buy a new one but expect $500 on up.  Even if you added one,
> you are still limited by the VNAs hardware.

The "transfer switch" is a 4 connector device.  It's electrically like a
"reversing switch" for DC motors. Inside, it's pretty simple, there's 4
striplines that alternately connect the 4 terminals.

if the terminals are ABCD, it's arranged like this:

A - B
|     |
C- D

and either AB and CD are connected, or AC and BD are connected. The
spacing between the connectors is equal, so the RF properties are well
matched.

(In waveguide, it's a bit different, and called a "baseball switch"
because there's a core that rotates 90 degrees. But the connectors are
the same, A connects to either B or C, and D connects to either C or B. )

I've had fairly good luck with used switches - I've never had a bad one
out of a few dozen.  I've had a couple where I couldn't figure out the
model number or wiring, or the case was beat up, so I sawed it open to
see how it worked.

Yes, new ones are *very* pricey.

And with used, you won't necessarily know if it's a 4 GHz or a 26 GHz
switch, or if it's 70 dB or 80dB isolation or something in between.



>
> While the software allows you to manually control the transfer relay,
> it expects it to be under software control when it's being used.  I
> have no plans to support a manual method.
>
> Depending on your wants/needs, you could wait and see what OWO brings
> to the table next.  Estimated price is around the cost of a transfer
> relay.  May be other benefits as well.  We have to wait and see.
>
> I've seen some pretty odd posts when it comes to making full 2-port
> measurements.  The best so far was one of the radio hobbyist
> suggesting to use two VNAs.  You can't make that stuff up.


Why not? I was the one who suggested it, and when I get some time, I'll
buy a second NanoVNA and try it.  No reason it won't work - at least to
the performance of the NanoVNA. Sure, I'm not sure it could be
calibrated to the level of the mmWave Keysight boxes at work, but maybe.
Won't know unless I try.

It *is* substantially cheaper than a transfer switch, computer
interface, and related stuff.  2 $50 VNAs and some Coax Ts, can't get
much simpler than that.

And your comment prompts me: I just ordered a second one. Probably won't
get around to testing until Friday.

Joe Smith 2021/08/31 04:34

>>... I found a Bird DPDT manual RF switch with N connectors which is low SWR...
>>OK, I don't like the Transco or Omron relays either.  What is your opinion regarding the suitability of the manual Bird RF switch ?

Still waiting on a part number and how do you even plan to connect it in the RF path?   Why would you ever consider something like this over using an actual transfer relay?

John Galbreath 2021/08/31 10:42

Bird switch I have is part # 72-2.  It is a 2-position, double pole, double throw, 50-ohm, manually-operated switch with 6 each N connectors.  The 1-GHz VSWR is 1.06.  Cross talk is 75 db down - insertion loss is 0.09 db @ 1 GHz.

Four good reasons to consider manual switch over automatic relay:

a.  I have this brand-new switch in my garage.

b.  I doubt my ability to design and build a working PC-USB relay control gadget.

c.  I rarely do 2-port manuevers.

d.  My wife wants me to spend more time with her and less time playing with my nerd toys.

Joe Smith 2021/08/31 13:47

And how would you propose to connect it into the RF path?  Can you hand sketch a drawing and attach it?

John Galbreath 2021/09/01 09:21

My guess is that my NanoVNA has about 50 db or less isolation between ports with nothing attached.  The Bird switch has 70 db or better isolation with nothing attached.  If I add 2 coax jumpers with N-connectors where indicated at x and y without making crosstalk much worse, then I would suggest a path as shown in the attached figure.

Was this a trick question ?

Joe Smith 2021/09/01 10:56

It's what I was expecting.  I had posted what I suspected were the two proposals here:

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3659584/#msg3659584

Maybe we will get some feedback.

Joe Smith 2021/09/04 07:45

Too bad, zero feedback outside of Jim joining up.  Assuming you read my posts, you know my main concern with your manual switch is the unterminated stubs you are adding to your RF path.  With the two VNAs and Ts, there are many other concerns I mentioned which includes also adding stubs, 25ohm mismatch and running the two VNAs async.   I mentioned using a couple of splitters to at  least keep with a 50 ohm system but the losses would be poor.  All pretty basic and I wouldn't think you would need to buy a second VNA to prove it was a bad idea but Jim was running experiments at the time.   Sadly they never posted any results.

If you wanted to try your DPDT switch and Ts, consider the cost of the connectors, Ts and cables.  Keep the connections short but don't exceed the bend radius of the cable.  Try it over the frequency range you are planning to work in.  I assume with you posting with the V2 group you are working at frequencies that this will be important.    You would need to save two calibrations and load them manually.  Of course, that's not going to get the T-check working with my software.

Jim Lux 2021/09/04 08:17

On 9/4/21 7:45 AM, Joe Smith via groups.io wrote:
> Too bad, zero feedback outside of Jim joining up.  Assuming you read
> my posts, you know my main concern with your manual switch is the
> unterminated stubs you are adding to your RF path.  With the two VNAs
> and Ts, there are many other concerns I mentioned which includes also
> adding stubs, 25ohm mismatch and running the two VNAs async.   I
> mentioned using a couple of splitters to at  least keep with a 50 ohm
> system but the losses would be poor.  All pretty basic and I wouldn't
> think you would need to buy a second VNA to prove it was a bad idea
> but Jim was running experiments at the time.   Sadly they never posted
> any results.
Probably this weekend.. got busy with work. I have my two NanoVNAs, I
have my Ts

Joe Smith 2021/09/21 10:43

On Sat, Sep 4, 2021 at 11:17 PM, Jim Lux wrote:

>
> On 9/4/21 7:45 AM, Joe Smith via groups.io wrote:
>
>> Too bad, zero feedback outside of Jim joining up.  Assuming you read my
>> posts, you know my main concern with your manual switch is the
>> unterminated stubs you are adding to your RF path.  With the two VNAs and
>> Ts, there are many other concerns I mentioned which includes also adding
>> stubs, 25ohm mismatch and running the two VNAs async.   I mentioned using
>> a couple of splitters to at  least keep with a 50 ohm system but the
>> losses would be poor.  All pretty basic and I wouldn't think you would
>> need to buy a second VNA to prove it was a bad idea but Jim was running
>> experiments at the time.   Sadly they never posted any results.
>
> Probably this weekend.. got busy with work. I have my two NanoVNAs, I have
> my Ts
>
>>
>> If you wanted to try your DPDT switch and Ts, consider the cost of the
>> connectors, Ts and cables.  Keep the connections short but don't exceed
>> the bend radius of the cable.  Try it over the frequency range you are
>> planning to work in.  I assume with you posting with the V2 group you are
>> working at frequencies that this will be important.    You would need to
>> save two calibrations and load them manually.  Of course, that's not going
>> to get the T-check working with my software.
>
>

Did you get any further with your testing?

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