Topband: Checking the integrity of 75 ohm cable

[Jim Brown]

On 10/16/2020 1:26 PM, Gary Smith wrote:
> What would be an easy way to tell if these
> coax have been damaged in some way?
> 
> I do have an old MFJ-259B

That might give you a clue if the cable is open or shorted, but it's 
unlikely to show chewing that doesn't cause an open or short, but allows 
water intrusion, etc.

The best tool is a vector analyzer that includes software/firmware with 
a very good TDR function. I use the VNWA3EC, built by hams in the UK 
from a design by DG8SAQ, who also does both firmware and software.

https://www.sdr-kits.net/DG8SAQ-VNWA-models

The TDR function in this unit is really excellent, and can be used with 
the antenna connected. The procedure is to do a very wide sweep (I 
usually sweep 50 - 500 MHz) so that fine detail shows up clearly. 
Software then does an inverse FFT on the sweep to get the TDR, and 
allows the user to choose which of five different windowing functions 
provide the clearest view of the measurement.

There are ultra-cheap VNAs around, but I don't know the capabilities of 
their operating software.

One way I test my RX antennas is to use them to listen on the AM BC band 
while I switch directions, using this FCC website to tell me who is 
where on each frequency.
https://www.fcc.gov/media/radio/am-query

73, Jim K9YC