Author Topic: Feedline measurements  (Read 691 times)

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Offline dobsonr741Topic starter

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Feedline measurements
« on: May 10, 2024, 02:04:55 pm »
I'm setting up a feed line from my office to the attic reusing existing RG6 segments. How can I measure reflections/loss/etc by hooking up to nano VNA, but having access to only one end at a time? I expect it to work from 20m to 2m only for QRP powers.
 

Offline mag_therm

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Re: Feedline measurements
« Reply #1 on: May 10, 2024, 03:51:18 pm »
Put a 50 Ohm terminator on far end.
Sweep Z of S11 using just Ch0. However that won't give the loss, as S21 needs both ends at the cable to be connected.

Edit Sorry , RG6 is 75 Ohm.
« Last Edit: May 10, 2024, 03:53:31 pm by mag_therm »
 

Offline Roger Need

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Re: Feedline measurements
« Reply #2 on: May 10, 2024, 04:53:58 pm »
I'm setting up a feed line from my office to the attic reusing existing RG6 segments. How can I measure reflections/loss/etc by hooking up to nano VNA, but having access to only one end at a time? I expect it to work from 20m to 2m only for QRP powers.

If you leave the far end disconnected you can use the NanoVNA to make the equivalent of a Time Domain Reflectometer (TDR) measurement.  This feature is built into the NanoVNA and you will see impedance bumps as blips on the display.   If you have  a short or an open in the line you will easily see it.  Using the cursor you can measure the distance to the blip.

You can measure loss vs. frequency by doing a Return Loss (RL) measurement with the NanoVNA.  Leave the far end open and divide the RL by two to get an estimate of attenuation loss in the cable.  For best results measure with the far end open and then measure with the far end shorted.  Then Atten. = (RLo +RLs)/4.  Attenuation estimate will be better

If you have a recent version of firmware by DiSlord you can measure several things about your cable by leaving the far end open and using the Cable menu item (under measure).

Roger
 


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