Topband: Checking the integrity of 75 ohm cable

[Michael Walker]

RigExpert has a variety of Antenna Analyzers that have a built in TDRs.

I highly recommend them.

Mike va3mw

On Fri, Oct 16, 2020 at 5:15 PM Jim Brown <jim at audiosystemsgroup.com> wrote:

> 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
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