Coax question ??

[johnyb-21]

I am installing dual antennas on my truck. I have access to lots of RG-59/U (75 ohm) coax. Can I run this coax from both antenna's and use a "T" adapter to connect to the radio, or will it be more desirable to go with a mini 8 (50 ohm) co-phase coax ???

[Phaze91460]

You need to run co-Phaze-ed ( HEHEHEhehehe ) coax. Sorry, had to through in the pun.

[316]

Problem with running duals is that you will pull more from one side of the truck rather than equally working cohesively. I can't remeber completley how it works but I know it kinda acts like a set of beams on a base station.
Is that hard to understand. I'm not sure I explained that correctly.
73's

[Bigpimp347 [UK]]

if running two antennas it's like this..
if both are mounted on teh mirrors, then the TX and RX signals will work greatly in a front to back direction, so like a beam.

you will also have to co-phase both to work together,
meaning length of 50ohm coax (RG58) to a 'T' connector,
the 2 pieces of 75ohm (RG59) measured 1/4wave of the operating frequency so around 106" EACH..going to each antenna mount.

then you put a 50ohm load on the end of one 75ohm coax and SWR the other antenna for lowest SWR, then you remove the 50ohm load and put on the other 75ohm coax, and put the antenna (un SWRed) on the first mount and SWR the second antenna.

you then have both antennas with the lowest SWR on the working frequency, and should be phased to work together.
but the ideal spacing should also be 1/4 wave length apart for the antennas, buy not many cars have 106" roofs !!!

or just buy a co-phasing harness..!!
but you still have to SWR each antenna..

[058hamer]

Great tip on the dummy load. 058hamer

[johnyb-21]

Sounds a bit more technical than I thought, but hey, I'll give it a shot. Where would I find a 50 ohm load to put in place of the antenna ??

[Bigpimp347 [UK]]

a 50ohm load or 'dummy load' shopuld be easy to find,
try fleabay for them, around $15 for a cheap one that'll do say 30w 60w maximum, or there's the simple lightbulb types, these handle around 5w,

you can buy the harness too, i'm sure hy-gain and avani did them, there's even 10mtr ones around too..

but load look for dummy load, cheap and always handy to check your rigs power into, so you have an accurate 50ohm, unlike doing it into a antenna that can give false readings..