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NanoVNA V2+4 SMA load


Mike Wyatt 2020/12/06 13:46

Just received the mentioned V2+4 VNA and decided to check the supplied SMA 50 ohm load that comes with the cal kit. I measured 50.931 ohms with a new KS34465A, which is considerably higher than the type N load supplied with the SSA-2N version which is 49.634 ohms. Measurements were conducted with the supplied Short establishing the Zero ohm reference for the SMA, and using the type N short for the N Zero ohm reference.

What are others finding with the cal load supplied with the various NanoVNA?

Best,
--
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

aleatorii.yg 2020/12/07 03:37

Mine is 50.7 ohms, measured with a Fluke 21, with lead impedance subtracted.

Mike Wyatt 2020/12/07 07:29

Wonder what the "Precision" Cal kits measure?

--
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

Randy True 2020/12/08 15:15

50.4 with the supplied N load.


Randy W4RTT

Mike Wyatt 2020/12/10 06:41

I've asked the OEM for the V2+4 NanoVNA version about the ~51 ohm SMA load (DCR 50.931 ohms), and was told this is correct, and they use this 51 ohm SMA load to help improve the HF RL to better than 35dB. I've made some LF measurements with the V2+4 calibrated with the supplied ~51 ohm SMA load and with another SMA (DCR 49.687 ohm) load, these were compared at 10MHz to a SAA-2N calibrated with the supplied type N load (DCR 49.643 ohm) and a Siglent VNA. These results show the measured impedance follows the basic DCR load difference from 50 ohms. The V2+4 with the 51 ohm load had a almost constant impedance magnitude difference of -0.6 ohms compared with the SAA-2N and VNA readings (which were much closer). However, when calibrated with the other SMA (DCR 49.643) this difference was much lower (almost identical with the SAA-2N) as expected, even so at 100MHz.

Apparently a simple DCR measurement of the cal load can provide a hint of the expected error of LF impedance measurements around 50 ohms (maybe even yield a correction factor), but not a substitute for a quality cal load.

After the holidays I plan on going over to the university and one of my old grad students has offered to help with a cal transfer to the devices I have, so will have access to a few quality cal kits and lab VNAs.

Best,

--
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

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