cb antenna mount location help needed

[bansil]

Our Expo vehicle is rather large and all metal (it's a 8ft wide 40 ft flat nose bus) exploring is still exploring right?:coffeedrink:

I have read about ground planes and antenna radiation patterns enough to confuse myself

I have talked to a couple cb shops and have gotten way different opinions

I believe the best spot for an antenna would be on top but at 10ft tall I would be hitting everything with a 4 ft stick and destroying it would be easy (would a 2ft be tall enuf?)

mounted either front or rear on the bumpers would require very long antennas to get over the roof (to give opposite end coverage)which of course would hit everything

So I was told dual antenna's mounted on the mirrors would work great since I am so wide, I have read alot of negatives on dual side mounts with all the metal availible to screw up the rf radiating properly

I only want a nice reliable 5-10 mile distance on flat open roads

Any recommendations?
Sorry for long post

 

[k9lestat]

i wonder if you could run dual whips or fire sticks on opposing corners at opposite ends of the vehicle? just wondering.

 

[Hill Bill E.]

Dual antennas off the mirrors would be your best bet.

Here is some great reading and info from Firestick, on setting up antennas, and tuning them properly.

Firestick

 

[bansil]

Thanks for the link,I was reading that site yesterday,first place I went after here(of course) firestiks have been on all my rigs except the K40 and prior the 10 foot steel death whip.

I ordered an SWR meter yesterday, figured cheap insurance towards a good install, and it was always a pain to find someone with one.

I read somewhere 104" between and 108" between them mounted.

 

[BigJimCruising]

"I only want a nice reliable 5-10 mile distance on flat open roads"

On CB that's not going to be a reliable distance even with the best of conditions. Most of the time 1 to 2 miles is about the best you will do. I tell you that so you don't get your hopes up. CB just doesn't typically work that well.

Given your type of rig I'd shop around for a good base loaded 5/8 wave whip antenna. (I've heard the Wilson brand is pretty good but don't know first hand) Find a spot near center of the rig to mount it. Tune it for the best match you can get. This will let you drive under gas stations and bridges with only the metal whip hitting and the base load will give you a decent signal out. Not the best setup but will do. The dual antennas is more for the "trucker" look then any great gain in signal output.

 

[Tennmogger]

BigJim gives good advise. Dual antennas 'look' good but making them work requires an impedance matching harness (to get back to 50 Ohm feed again after paralleling two 50 Ohm antennas) and the combined pattern is probably in the wrong direction anyway.

Top center is the best place. Larsen makes some really good base loaded whippy whips. If you need a source check out Ham Radio Outlet www.hamradio.com. The model that covers 10m ham band can cover the CB band by adjusting initial cut length. My Larsens have survived trail use for years.

You can have a long row of antennas down the center line of that bus!!!

 

[Finlay]

So I was told dual antenna's mounted on the mirrors would work great since I am so wide, I have read alot of negatives on dual side mounts with all the metal availible to screw up the rf radiating properly

I only want a nice reliable 5-10 mile distance on flat open roads

Any recommendations?
Sorry for long post

Any mobile antenna is a bag of compromises. You'll just have pick which limitations you prefer to live with.

I think dual mirror mounts are probably your most practical bet. It's what semis do - for a variety of reasons - and they get acceptable performance pretty easily. I run dual sticks on my pickup with good results, too.

If it is the sort of bus I think it is, 3 foot sticks will work OK, but 4 is better. But if you get a foot or two above the cabin, you'll be fine.

The other advantage is having far less cable to run. If you have to go to the middle of the bus, well, that's a lot of coax.

Anyway - it's easy to overthink this. The CB is only 4 watts; at some point the receive gain on the other end will be far more important than any incremental gain on the transmit side.

 

[GlennA]

Have you considered a single mirror mount? I have run dual mirror mount and single mirror mount in the past. I could see no significant difference in performance. When using a single mirror mount, I mounted to the mirror that I thought would see the least traffic. On my truck that was the passenger (right) side, on your bus it may be the driver (left) side. One thing to consider is the antenna overall height. Most highway bridges are at least 13'6". Anything over 13'6" is considered overheight. Hitting an object at highway speed with the antenna will damage any antenna. A fiberglass antenna will probably break, a steel whip will just end up significantly disfigured but may still function. Just my .02.

 

[bansil]

I have 1 3ft firestick I may just experiment and mount it on the pass mirror and buy new coax and "see" how it works.
With everything I've read,good coax,above the roof 2ft,swr meter to check and tune and my multimeter to check the mounts connection(I'll run a ground wire from the mount to the body/chassis) like firestick reccomends,I will have a good base to start with
Thanks for all the help!
Sometimes reading everything makes you turn something simple into a "what if"

 

[DaveInDenver]

Have you considered a single mirror mount?

This is the way I'd go. Use the longest one that is practical and keeps you from hitting too many overhead signs and stuff. Probably about a 5 or 6 foot tall antenna. All mobile installs are compromise, so the end result is a mix of being able to live with it daily vs. performance. There are too many variables using dual radiators and they can be touchy about tuning. Even commercial broadcasters and stationary amateurs have headaches keeping multiple elements tuned on fixed towers, forget moving with them flopping around through all sorts of weather and environments.