Dual Band Antenna Mounting Location?

[kjp1969]

Ham gurus: Advice sought!

I've already talked to Cobra and Wilson, with ambiguous responses to this question. At present, I have a Wilson 1000 CB antenna with a 60" whip in a through-the-roof mount. It's visible in the photos below and works very, very well. I'd like to mount a dualband 2m/70cm antenna somewhere on the truck to use with a 55 or 75w 2m radio. Another through the roof mount would be fine, but it would have to be right next to the CB antenna in order to allow for the (huge) cargo box. Would the two interfere with each other if they were 12" apart? Unlike the CB, the Ham antenna would live on the truck full time, and if on the roof would have to be springy or fairly low profile to allow me to park in underground garages.

Alternatives include putting the Ham on the tab where the work light is mounted on the spare tire carrier, putting the CB there and using the roof mount for the Ham (would hate to lose the range of the CB with the good roof ground plane), or possibly a hood lip mount for the Ham and leave the CB where it is.

Photos for reference. In the high overhead shot, my bronco is in the middle. The box takes up most of the roof space on the passenger side.

 

[Fish]

The roof is better, but you may have some interference with the CB antenna. Keep them as far away as possible. I think I've heard one bandwidth is preferred. That being said, my work Suburban has around 5-6 antennas on it and they all seem to work OK.

As far as low profile, you could use a Larsen low profile antenna most of the time and switch to something else when warranted. http://www.larsen-antennas.com/docfiles/ASB10/SalesSheets/LOWPRO.pdf

You could also look at a hood lip mount or something like that.

 

[kjp1969]

The roof is better, but you may have some interference with the CB antenna. Keep them as far away as possible. I think I've heard one bandwidth is preferred. That being said, my work Suburban has around 5-6 antennas on it and they all seem to work OK.

As far as low profile, you could use a Larsen low profile antenna most of the time and switch to something else when warranted. http://www.larsen-antennas.com/docfiles/ASB10/SalesSheets/LOWPRO.pdf

You could also look at a hood lip mount or something like that.

I agree- the options are numerous. I'm looking for advice on which way to go. Will the 2 antennas on the roof next to each other interfere with each other? Does 2m need a ground plane like the CB? Will the roof be appreciably better than the tire rack or hood?

 

[H0LLYW00D]

here is how close I have my antennas and I have not gotten any interferance from either one. (Left is quad band and right is CB)

 

[kjp1969]

here is how close I have my antennas and I have not gotten any interferance from either one. (Left is quad band and right is CB)

Thanks; that's good to know. The sales guy at the Ham shop mentioned that he had two Ham antennas next to each other on similar freqs and one radio burned up the other. That was similar freqs, which I'm sure is the reason- One pumping out 55w right next to another receiving it.

 

[Fish]

Typically speaking, the 2m antenna will require a ground plane just like the CB. That's why the roof is preferable. How far apart can you possibly get the antennas? Will you be using both radios simultaneously? Or one for traveling with one group and the other for traveling with different folks?

The roof does present a better ground plane than the hood or tire rack, assuming that the antenna is not mounted on the very edge.

How much do you really use the CB? Maybe move that antenna to the tire rack if it's just for up close stuff and put the 2m on the roof?

I'm suffering from the same dilemma you are, except I have a giant camper shell to contend with. Debating if I should put the antennas (way) up on top of the camper, or on the truck roof. The top of my camper is around 8' in the air, so branches are a huge concern.

 

[kjp1969]

How much do you really use the CB? Maybe move that antenna to the tire rack if it's just for up close stuff and put the 2m on the roof?

That's what I'm thinking. The Wilson 1000 lives in the garage except for a few trips per year. I'd leave the Ham ready to operate or operating at all times.

I'm told that you can actually get a burn from a bare metal 2m antenna when its transmitting- another good reason to keep it up and out of harm's way. But better still would be to have them both up there.

 

[1911]

Will the 2 antennas on the roof next to each other interfere with each other?

The 2m radio on anything more than the lowest power setting will push through any squelch setting on the CB so you'll get a big burst of static through the CB receiver when you key up the 2m. The CB will not affect the 2m much because cb is only 4 watts max.

Does 2m need a ground plane like the CB? Will the roof be appreciably better than the tire rack or hood?

Yes and yes. You can run a 1/2-wave 2m antenna with minimal ground plane like on a tire rack but you will get noticeably better 2m performance with a 5/8-wave antenna on the roof.

 

[xtatik]

I'm told that you can actually get a burn from a bare metal 2m antenna when its transmitting- another good reason to keep it up and out of harm's way. But better still would be to have them both up there.

RF exposure and burns are covered in the study material and practice tests for the Technician class license. You might want to give it a read before powering up.:coffeedrink:

 

[kjp1969]

The 2m radio on anything more than the lowest power setting will push through any squelch setting on the CB so you'll get a big burst of static through the CB receiver when you key up the 2m. The CB will not affect the 2m much because cb is only 4 watts max.




Yes and yes. You can run a 1/2-wave 2m antenna with minimal ground plane like on a tire rack but you will get noticeably better 2m performance with a 5/8-wave antenna on the roof.

Thanks for the helpful comments. I can separate them by 6 feet or so by going roof/tire rack. That's about the best that I can do. It kills me to dismantle the CB setup when it works so well, but I want to favor the Ham with this new install.

 

[kjp1969]

So before I head off to the Ham shop, can anyone answer me this: Is the through-the-roof antenna mount that I installed in a 3/4 inch hole to mount my Wilson 1000 the same as the mount that I will use to connect a dual band antenna? In other words, can I hook up the new Ham antenna to the old mount/coax without changing it?

 

[1911]

So before I head off to the Ham shop, can anyone answer me this: Is the through-the-roof antenna mount that I installed in a 3/4 inch hole to mount my Wilson 1000 the same as the mount that I will use to connect a dual band antenna? In other words, can I hook up the new Ham antenna to the old mount/coax without changing it?

It sure SOUNDS like a standard NMO mount but I can't be 100% sure from your description alone - a photo would remove all doubt. An NMO mount is great for 2m/70cm and gives you the widest range of choices for antennas. Single-antenna cb and 2m/70cm ham both use 50-ohm coax so you're good there too.

 

[kjp1969]

It sure SOUNDS like a standard NMO mount but I can't be 100% sure from your description alone - a photo would remove all doubt. An NMO mount is great for 2m/70cm and gives you the widest range of choices for antennas. Single-antenna cb and 2m/70cm ham both use 50-ohm coax so you're good there too.

Excellent- I'll got to the Ham shop with that in mind and confirm there. I don't have a photo with the antenna off.

 

[1911]

This is an NMO mount (albeit in a bracket instead of through a roof):

 

[fire931]

The standard Wilson through the roof mount is totally different from an NMO mount. They do however share the same size hole so you can swap them out.