Products > Test Equipment
Copper Mountain Technologies VNA
G0HZU:
--- Quote from: tomud on August 03, 2023, 06:49:08 pm ---As for the VNAs described here, I'd rather see sample measurements than opinions. With a description of what calibrators, test leads, etc. were used.
--- End quote ---
One interesting test would be to measure a DUT (from a cold start) with an old stored calibration using the same test fixture.
Looking back through my recent files, I measured an HP 8120-4781 cable back on the 26th July with my old E5071 VNA. This would have been calibrated using an unknown through cal after the analyser was allowed plenty of time to warm up.
Today is the 4th August and I fired up the VNA and loaded up the 8 day old cal corrections and measured the cable again today from a cold start. As soon as the VNA would let me, I took a plot of the cable. This can be compared with the original measurement out to 3GHz.
There's bound to be some phase shift even though I used the same decent HP cal cable (the same way around) as last time but I would expect the amplitude agreement to be really close even though the cal was done 8 days ago and I'm also comparing cold to the original cal 8 days ago (note: the analyser was fully warmed up 8 days ago when the calibration was done).
There's about an hour between the cold and the warm test today. The Cal plot is the 8 day old data for the same cable.
I used a decent HP N cable as part of the initial calibration. This cable is in very good condition and gives repeatable results up to 3GHz although some minor differences are inevitable across 8 days and through removing and reattaching the cable. The main aim is to show the change in drift from cold to warmed up (today) to show how stable the VNA is from a cold start onwards.
Sadly, I did knock/move the cable between cold and warm so I'd really like to repeat this again and make sure I don't touch anything.
To clarify, the warm test was taken about 1 hour after today's initial cold test. The Cal plot is the original from 8 days ago.
The results below are quite good I think. There is hardly any drift at all between all three cases. The E5071 is a very old VNA so I'd expect any modern alternative to be able to compete well against this old workhorse.
tautech:
--- Quote from: G0HZU on August 03, 2023, 05:02:58 pm ---Also, my main desktop PC is in the opposite corner to the VNA in my workroom now. So any cable routing would be a pain.
--- End quote ---
Have you considered a WiFi solution, something you can easily open and close at will ?
Away from the bench/lab I often need a LAN connection but cabling is 10m away and sneakernet was the normal solution until another member suggested using one of these in Client mode:
https://www.tp-link.com/us/home-networking/wifi-router/tl-wr802n/
Found I can power it from an instruments USB port too and it's invisible to the network.
So armed with the instruments IP and especially when you have a well featured webrowser remotely accessing instrument files is now a breeze which also saves on sneaker rubber. :)
G0HZU:
Thanks, yes I've thought of other ways to do this. All of them are more efficient but I don't want to network the Win 2k VNA. I can't avoid the trip across the room anyway.
I did an insertable device calibration last night and measured a nice 10dB attenuator up to 6GHz. I left the cables and attenuator in place overnight. At around lunchtime today I powered up the E5071 VNA and loaded the previous cal into it and immediately measured the 10dB attenuator.
The first plot shows the difference between last night and the initial cold measurement today. This is a really harsh test but I think the VNA did OK here.
The second plot shows the response after a short warmup and then at +3 hours and +5 hours. This looks a lot better. Hardly any drift at all.
This is only a scalar measurement of s21 though. Usually, I measure two port models of semiconductors (eg BJT or FET) and this involves measurements near the edge of the smith chart with a reflection coefficient very close to 1 at some frequencies. This is where I really need the stability of the E5071 VNA. It does seem to do a good job when measuring semiconductors up to many GHz.
G0HZU:
Note that this is an N type attenuator. The fine trace ripple seen above about 4GHz is probably due to the limits of my homebrew N type cal kit. I have worked out the Cx and Lx coefficients for this cal kit out to 6GHz and it does use extremely nice Suhner 18GHz N connectors with 8 slits in the female centre contact for example. I used very expensive N connectors in the cal kit. They are similar quality to decent VNA N connectors. Now that it is corrected, this cal kit does work extremely well. But not as well as a decent Keysight N cal kit.
I do have an Anritsu N kit but it doesn't offer male and female calibration for an insertable device. I've got various cal kits for SMA and 3.5mm including an N4431B Ecal and an 85033E mechanical kit.
G0HZU:
All I meant to do in my last post was to add some background info about the calibration setup I used as requested below. I also used an HP 8120-4781 N cable as part of the test setup.
This cable is old but still quite good. I don't have any $$$ metrology grade N cables here but this one should be quite stable over time if not moved.
--- Quote ---With a description of what calibrators, test leads, etc. were used.
--- End quote ---
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