开云体育

Here is another application for nanoVNA.

I own a Narda 3060-20 directional coupler that I have not been able to find directivity information on. The coupler has a 10-200 MHz frequency range and a -20 dB coupling factor. The test setup photo is attached.

Test procedure:

1. Connect nanoVNA CH0 to the output port of the coupler under test.
2. Connect nanoVNA CH1 to the coupling port of the coupler under test.
3. Leave the input port of the coupler under test open.
4. Turn on the nanoVNA
5. Set the nanoVNA to display CH1 LOGMAG only to reduce screen clutter.
6. Set the start and stop frequencies of the nanoVNA as appropriate for the coupler.
7. In the nanoVNA CAL menu select "RESET" and then select "Calibrate-Thru" and "Done".
8. Back out of the menu to the main CH1 LOGMAG display (Should be a straight line at 0 dB, see photo 1).
9. Connect a 50 ohm load to the input port of the coupler under test.
10. Use the marker to read the coupler directivity off the displayed response (see photo 2).

The measured directivity of the Narda 3060-20 was 30 dB at 10 MHz and 22.5 dB at 200 MHz. The minimum directivity for a reliable measurement is 20dB, and 30dB or larger for the measurement of well-matched devices. Hope this info is useful to other nanoVNA users.

At step 3 you can also use a shorted load. Then you have directivity for short. The two should be close about 0.5 dB. Also reverse IN and OUT to check symmetry.

30dB is rather low for 10MHz. I can get 53dB at 10MHz and 37dB at 35 MHz but this was not measured with the nanoVNA.

tuckvk3cca,
Thanks for the feedback. I finally was able to find a directivity specification of 20 dB minimum for the Narda 3060-20 on the web, which is in agreement with my measurement made using the nanoVNA. My best directional couplers have a 40 dB directivity. The ones I own with a directivity below 20 dB I only use for indicative purpose.

Hello hwalker,
Thank you very much for this useful application note.

I very much welcome the fact that not only the measuring setup was described in detail,
but also the measuring result was evaluated in detail.

I think it makes sence to put the contents in a PDF document and copy it in the files section of this group.

73, Rudi DL5FA

Rudi,
I totally agree with you than an applications note section would be a welcome addition to the "Files" category of this user group. The group is approaching 3000 messages and it is getting harder to use the search button to locate specific content . A lot of new users come here with some familiarity using antenna analyzers, and zoom in on the SWR measuring capabilities of the nanoVNA. It is only after being exposed to the nanoVNA's numerous measuring capabilities by other users, that they come to realize the nanoVNA also can measure tdr, attenuation, gain and impedance. At $50, it provides a cheap hands on education that can help to improve your job skills or better enjoy your hobby.

Here is my RF-bridge measurement. I have blue RF-bridge with two installed jumpers.

I'm using more standard RF bridge measurement method:

1) Open CAL menu and calibrate OPEN/SHORT/LOAD as usual
2) Connect two 50R terminators to CH0 and CH1 and calibrate ISOLN
3) Connect CH0 to the bridge Input
4) Connect CH1 to the bridge Output
5) Connect 50R terminator to the bridge REF
6) Leave bridge DUT connector open
7) Calibrate THRU and then press DONE and close (no need to save)
8) Connect second 50R terminator to the DUT connector
9) Measure S21