Topband: Topband Digest, Vol 214, Issue 17

[W3HKK at roadrunner.com]

I have an AA54. It provides TDR graphing of your coax and can identify
damage areas by distance and Z.

With a multimeter, short the far end and measure d c resistance. and
compare to the specs. 

Not a bad idea when installing new coax is measure its resistance and
Zo and keep in a card file for future comparisons. 

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Sent: Saturday October 17 2020 12:00:42PM
Subject: Topband Digest, Vol 214, Issue 17

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 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.
  >
 > 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.
 >  Reflector
 >

 ------------------------------

 Message: 4
 Date: Fri, 16 Oct 2020 18:40:49 -0600
 From: Don Moman VE6JY 
 To: topband 
 Subject: Re: Topband: Checking the integrity of 75 ohm cable
 Message-ID:

 Content-Type: text/plain; charset="UTF-8"

 Try to find/borrow a older Tek 1502 TDR, they are inexpensive on ebay
 (~$100) and show way more detail than any of the analyzers I've
tried.

 73
 Don VE6JY

 On Fri, Oct 16, 2020 at 5:50 PM Michael Walker  wrote:

 > 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 
 > 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.
 > >
 > >  

 ------------------------------

 End of Topband Digest, Vol 214, Issue 17
 ****************************************
 

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