SWR's

[Coax Kid]

Hi Guys
I have a Q. I have my radio (DX959) in my work truck KW and I have Co-Phase, When I check my swr's with the radio i have a good match, but when I put in the jumper to check with a ex. meter the match is off. My Q. is does the ohms make a dif. with the jumper being 50 and the Co-Phase being 75. I have 18' of co-phase and I think my jumper is 18" or 2' .


Thanks
Coax kid

 

[W5LZ]

The junction of the two 75 ohm feed lines isn't 50 ohms, close, but still not 50 ohms (never will be either). That means that adding or subtracting a length of 50 ohm coax used as a jumper for the meter, can make some slight difference in the SWR shown by the meter. It shouldn't be very much difference though! How big a difference are you talking about?
- 'Doc

 

[Marconi]

The results you are seeing are probably a sure sign that the co-phase harness is not doing what it should be doing and that is because of a mis-match in the system. Adding coax and moving your SWR meter to different positions in the system should not show dramatic changes in your SWR readings.

Check the SWR, or better still use an analyzer at the radio end of the harness. Let us know what values you get for your center working frequency, R, X, SWR. If you do have an analyzer scan for the same results for a value of R=50, or close as possible. Also scan a value for X=0 or close as you can. Don't forget to give us the frequency and let us know what kind of antennas you are using. Also let us know if the AT's are tunable or not? If they are did you pre-tune them individually?

 

[Moleculo]

I'm guessing that if he had an analyzer he would have used that instead of a standard SWR meter. We still need to know the answer to Doc's question.

 

[74IN]

Just lose an antenna.

Feed one, keep the other if you like the way it looks.

Trust the external meter, not the one in the radio.

Co-phase is over hyped.

 

[Marconi]

Well guys, I did a search on Co-phase and Kid Coax was trying to get this harness to work last year and your good ideas back then did not help solve his problem then either. 'Doc gave you a very good idea about what was needed. So maybe you should go back and study that thread and then reconsider what has been said here also.

See: http://www.worldwidedx.com/cb-antennas/27888-co-phase.html

I think that 'Doc also mentioned something about the possibility of a working harness ending up being too short for your big truck. He also suggested a solution. Did you consider or understand those comments? For these reasons I posted earlier that you harness is not tuned and is likely too long.

Also note that the harness you have may never work right unless it has the 75 ohm properties needed. A co-phase harness is not just a piece of coax between two antennas set 9' apart of a big truck. The harness is also not going to be 18' long for 11 meters and work as it should.