I did actually do that and was seeing about the same return loss. The plot is somewhat noisy and there is a periodic spike at perhaps 300 MHz as captured in the attached photo.
Peter
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On Aug 8, 2019, at 10:09 AM, tuckvk3cca <tuckvk3cca@...> wrote:
Would you be able to use your OSL load to calibrate the nano and then run a scan with it on the supplied dummy? A comparison of the plots ftom the nano vs the 8753 should be interesting. I note that you can get quite decent sma dummy loads with guaranteed swr <1.06 or 30.7dB for under $15. These are less fragile than the ones supplied. Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: Peter Gottlieb <hpnpilot@...> Date: 08/08/2019 03:52 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] Some basic load measurements I made some further measurements using the 8753 setup.I did the OSL cal on one port and looked at both the Smith chart as well as S11.I didn't bother with the cheap BNC load. I used averaging (16) to get more stable measurements.The Smith chart was of little use as each load showed up as a tiny one pixel dot almost exactly in the middle. However, it does display reactance values.All the values here are from the 8753.Load R Z contrib ohms value S11 @ 900 MHzOSL 50.000 0.0000 0.0000 H -76 dB (noisy)Nano 49.184 0.4255 76.942 pH -40.673 dBNarda 50.438 -33.203 m 5.3205 nF -47.356 dBTiny 49.389 0.5977 105.58 pH -40.678 dBNote the resistance values on the 8753 differ from the DC resistance somewhat, even normalizing to the OSL value. You can clearly see the OSL becomes the definition of 50 ohms and the S11 is at the analyzer noise floor.tuckvk3cca pointed out how the 1.02 SWR corresponded to a 40 dB return loss and he is spot on. The Narda shows the best return loss at 900 MHz of better than 47 dB.What would be considered a high quality load? The one that comes with the NanoVNA is not terrible considering the other tiny one I have, which has a NSN number on it, is very similar. Not that having a NSN number infers anything spec particular, but at least it will have a minimum set of specs so somebody thought about it.I note that the very small SMA terminations are slightly capacitive while the 1.5" long Narda termination (it probably has some power rating) is slightly inductive. These variations are too small to see on the Smith chart at regular scale.PeterOn 8/6/2019 10:43 PM, Peter Gottlieb via Groups.Io wrote:> Resending from website as it didn't seem to go through as a message. Also my pasted table from Excel lost formatting so I tried to fix it to be more readable.>>> I just did some very simple resistance and SWR measurements using a HP 8753ES with 85046A, resistance was measured using a calibrated Agilent 34401A in 4 wire mode.>> I did a very basic one port 3 point cal using a Anritsu OSL which is specified to over 3 GHz.>> I took measurements at 900 MHz.>> Load R ohms SWR SWR notes> OSL 50.052 1.001 Flat> Cheap BNC 51.104 1.908 Sloping up with freq> Nano load 49.044 1.019 Flat> Narda 12.4 GHz 49.536 1.018 Flat> Tiny SMA 50.787 1.009 Flat>>> I am guessing there is some significant reactive component in the BNC terminator. All three of the SMA loads showed a flat SWR with frequency so I'm thinking they all have a minimal reactive component.>> The difference in resistances while keeping SWR low was a bit of a surprise to me. The load that came with the Nano is over an ohm off of the load I used to calibrate yet the SWR remains at a low 1.019. Why is this? I did the math and surprisingly this is indeed correct, per calculation the SWR should be 1.021 vs my measured 1.019. I'd say this is darn close seeing one measurement is DC resistance and the other is at 900 MHz.>> So my conclusion is that SWR is not a sensitive number to see resistance differences.>> Once I read some of the references cited I can do some more advanced measurements.>> Peter>> >
