| Author |
Message |
    
Scoobydoo
Junior Member
Username: Scoobydoo
Post Number: 30
Registered: 8-2005
| | Posted on Friday, November 18, 2005 - 7:34 pm: | 
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Hi everyone, Im installing a radio and amp in my truck and was going to run 9 feet of coax from the radio to the amp and then another 9 feet of coax from the amp to the antenna. This would give me 18 feet of coax total. Is this right or do I need to run 18 feet form radio to amp and 18 feet from amp to antenna. I just want to do this right. also, where should I check my swr's and what length jumper should I use? Thanks for the help. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 914
Registered: 6-2004
| | Posted on Friday, November 18, 2005 - 9:03 pm: |
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Length is unimportant unless you have an impedance mismatch issue. In that case you would want to use a 1/2 wavelength multiple, and that length depends entirely on the velocity factor of the coax and the frequency you're going to use the most. |
Scoobydoo
Junior Member
Username: Scoobydoo
Post Number: 31
Registered: 8-2005
| | Posted on Friday, November 18, 2005 - 9:41 pm: |
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You lost me. LOL! |
Scoobydoo
Junior Member
Username: Scoobydoo
Post Number: 32
Registered: 8-2005
| | Posted on Saturday, November 19, 2005 - 12:11 am: |
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Ok, I have a question, how would I know if I had an impedance mis-match? I found a formula online for coax length using frequency, velocity factor etc. and it said 14.1 feet of coax. I am still unsure if I would need 14.1 feet from radio to amp then another 14.1 feet from a amp to antenna? Or do I use 7 feet from radio to amp and then another 7 feet from amp to antenna? I am confused on this whole coax theory. |
Tech808
Moderator
Username: Tech808
Post Number: 8400
Registered: 8-2002
| | Posted on Saturday, November 19, 2005 - 12:34 am: |
|
Scoobydoo,
Hook your radio up directly to your antenna or antennas and adjust your SWR for the LOWEST SWR reading you can get on channels 1-20-40.
It should be around a 1:1 or 1:2
Then hook a 3' foot length / jumper of coax from the radio to the amp and your Antenna to the output of the amp and check your SWR with the Amp on and keyed.
If it is higher then try a 6' length / jumper and if that does not work try as 9' jumper from the radio to the amp.
Trial and error by using different size jumpers and adjusting the antenna / antennas is the only way to get it right.
And make sure the Radio and Amp are grounded to the frame and your doors are shut when checking your SWR and nothing is close to interfere with your adjustments.
Lon
Terch808
CEF808
N9OSN |
