开云体育

Hi Bryan
You are forgetting that the female female adaptor has a delay which when removed shift the measurement plane away form the calibration plane.
I have a suggestion which work with good precision up to 100Mhz or even higher pending the expectations and what is mentioned under Note!!.
The proposal is the following:
1. Enable a phase trace with 1degree/division at reference point 5.
2. Enable a Display/Scale/Electrical Delay of 100ps.
3. Set the frequency range of interest e.g. 50KHz to 100MHz
4. Calibrate at the end of the test cable with the male calibration kit fitted to the female female adaptor and do not use the open adaptor from the kit, just leave the female female adaptor unterminated during open calibration. Save calibration to either 1 to 4.
5. Observe after the calibration that the phase trace is slanting slightly downwards with a phase of about 0.15dgree at 100MHz
6. Remove the female female adaptor and observe the phase trace raises upwards quite considerable as we removed the phaseshift for the female female adaptor.
7. mount the bulkhead/pcb edge adaptor to the test cable and now trim the Display/Scale/Electrical delay until the phase trace is horizontal with 0 degree all over the frequency range.
8. Now the measurement plane is to the rear of the bulhead/PCB edge adaptor without any parasitic component and accurate measurements possible.
9. Remember to remove the Display/Scale/electrical delay afterwards
Note !! The condition for getting the phase trace adjusted to 0 degree is the bulkhead/pcb edge adaptor must have a shorter delay than the female female adaptor. If not increase the 100 ps delay.
I recommend to use a better SMA testcable than the one supplied and if you have another Female Female aadaptor use it as the one supplied have excessive loss
Kind regards
Kurt
-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af bryburns via Groups.Io
Sendt: 6. oktober 2019 23:13
Til: [email protected]
Emne: Re: [nanovna-users] Inductor S21 measurement using nanoVNA

Hi, aa_talaat,

Here is a suggestion.

I would recommend that you connect the inductor from the center conductor of port 0 to the ground of port 0 with the shortest possible wires. If you could, I would recommend soldering it across an SMA female connector that directly connects to the location where you did the Open, Short, and Load calibration for S11. In your most recent pictures, with short cables, that would mean you use an SMA femaile connector and solder the part to the back of the SMA connector where you would normally mount it to the circuit board. As long as you connect to the same point as you did the open, short, and load calibration, the measurements should be pretty good. You can then measure the inductor directly by observing the S11 information.

Several of the programs (nanoVNASaver or nanoVNA_mod_v2 for example) will show you the equivalent parallel impedance of the device connected to port 0. What you should see on the Smith chart is a short at very low frequencies, say 50 kHz, (a dot near the left side of the Smith Chart) with an increasing impedance (primarily inductive reactance) of the device you have connected. On the Smith chart the plot should start near the left edge of the horizontal axis and proceed clockwise around the outer circle on the Smith chart as the frequency is increased. Based on what you have said, I wouldn't go much beyond 30-100 MHz as the stop frequency; however, experimenting with the stop frequency would be instructive regarding the device you are measuring. At some frequency, the inductor will appear as a very high impedance (this will be reflected by the plot going to the right side of the chart) because it will have a parallel resonance which is an indication of the amount of capacitance in your coil.

I hope this helps.

--
Bryan, WA5VAH