antenna spacing

[richingalveston]

I am planning to install 3 antenna on my cucv roof rack. A cb radio using a 3ft fiberglass whip. A 1 ft am/fm radio and a scanner radio. I do not have the scanner yet but I believe the antenna will be small.

Is there a required spacing for these antenna. I am building a post and a mount for all 3 antenna in the middle of my roof rack. I would like to put the antenna approx.. 6 inches between them with the CB in the center.

I do not have any experience with this so I am reaching out for suggestions.
Thank you,
Rich

 

[CliffSegar]

A 6" spacing would be extremely close. For receive, it isn't too bad, but the CB will be used for transmit. CB is limited to relatively low power (compared to amateur or military levels) but I would be concerned with substantially overloading the front end of the broadcast and scanner radio. Power decreases with the square of distance: double distance, a quarter the power. I would suggest the CB antenna in the center and the receive antennas at the far ends of your rack. (I am assuming a linear rack. In any case, separation from the transmitting antenna is your friend.)

 

[richingalveston]

Thank you for the input. I will put the CB in the center and the am/fm at the rear of the rack and save space at the front of the rack for the scanner.
With regards to the coax going to the antenna, does it matter if all the wires are in the same conduit. I will have a piece of seal tight running up to the roof rack from the engine compartment that will have all of the wires in it. The seal tight will run behind the snorkel so it will be hard to see but I really only have one path at this time to the roof rack.
Thank you,
Rich

 

[CliffSegar]

As long as your CB antenna is tuned (lowest SWR) properly, having all the coax in a bundle is fine. When going for the lowest SWR, tune the antenna - not the coax. (IE: don't cut the coax for lowest SWR. If the antenna is correct, the coax length does not matter.) Use good quality coax. If you can find LMR-195 or -200 (same size as RG-5, use that. LMR-240 is the size of RG-8X but would be overkill for what you are doing. I like the LMR variety because it is 100% shield - actually braid over foil. And they have good quality control. Putting them all in a loom will dress them nicely. Obviously, allow a bit of slack in areas subject to flex.