The AM Forum
March 28, 2024, 07:47:51 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: COAXIAL CABLE FAILURE  (Read 2156 times)
0 Members and 1 Guest are viewing this topic.
KB5MD
Contributing
Member
*
Offline Offline

Posts: 614


« on: October 09, 2017, 12:25:48 PM »

I have a vertical array on 80m.  The coaxial lines are buried leading to the vertical elements.  All the antennas are tuned to a low SWR for the same frequency but the swr is different
on the opposite ends of the various coax leadins at the connecting points on the phasing box.  I am using a comtek box in the center of the array.  My question is what method to use to determine if the coax to each element is bad.  They are not shorted, just high SWR on two of the four and the remaining two are not equal in SWR.  All the coax leadins are custom made to exactly the same lengths and did work fine until the SWR went crazy.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2648


Making AM GREAT Again!


« Reply #1 on: October 09, 2017, 12:46:46 PM »

TDR or mfj259 or darn near any other vna would work.

--Shane
KD6VXI
Logged
w1vtp
Member

Offline Offline

Posts: 2638



« Reply #2 on: October 09, 2017, 02:30:22 PM »

Roll your own TDR:

https://www.allaboutcircuits.com/projects/build-your-own-time-domain-reflectometer/
Logged
WA2SQQ
Contributing
Member
*
Offline Offline

Posts: 1090


« Reply #3 on: October 09, 2017, 03:21:30 PM »

Even easier
https://www.youtube.com/watch?v=9cP6w2odGUc
OR
https://www.youtube.com/watch?v=I1gfUNh5PJQ

Logged
W1ITT
Member

Offline Offline

Posts: 573


« Reply #4 on: October 09, 2017, 03:23:41 PM »

A simpler and dirtier method would be to put a dummy load at the far end of each  cable and measure the SWR. If the you don't have low level test equipment, you can jump the main transmission line from the shack into each of the feeders in turn, terminating them in the dummy load where the vertical element would be, and use the station exciter to measure.  It will involve a few back and forth trips but we can all use the exercise.   Remember, we are talking about 80 meters here, so some pigtail connections would be just fine.  Under "normal" conditions, a cable should be OK at amateur power levels unless it has gotten seriously wet, or bitten by a critter, but lightning just loves 4-squares, and Thor will have his way.  I like my TDR and network analyzers, but sometimes expedient methods are in order. Don't over-geek the problem.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.053 seconds with 19 queries.