Quote:
Originally Posted by Iraqvet05
I wouldn't think attaching a TT would change SWR unless your antenna is near the back of your truck. I have a VHF (2 meter) ham radio in my truck on a fender mount but I've never used it with the TT attached. I assume you will experience some directional blocking...I know I do when I pull up close to my aluminum garage door.
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X2. Many moons ago I installed a bazillion CB radios as well as Ham/Amateur equipment in vehicles. RV's were always a challenge. The travel trailer is quite a large shield back there. As far as SWR I'd just test it to find out. Test with and then without the trailer - nothing like a real-world test! I'm not sure what you are using for an antenna, but if you do need to compensate SWR with the trailer there, you might get lucky and be able to either raise or lower the antenna For one or the other condition. Just mark the whip for each condition so you know where to put it back to.
Back to the large shield that you are towing. I had varying degrees of success by going to an alternate antenna on the roof of the RV. The big issue here is the lack of a ground-plane. Some might not know it but a single antenna requires a good metal conducting surface underneath at 90 degrees to facilitate the signals propagation. The roof of an RV is usually not condusive to this as the surface is typically not a good conductor. Even if it has an aluminimum skin underneath the rubberized coating, aluminimum is a poor conductor.
Think about how the big-rigs tackle this issue. You'll mostly see that they use large twin antennas on their mirrors. This configuration creates a propigation in a figure 8 pattern. So while you create great directionality the pattern will go forward and behind - up and down the highway (let's not talk about switchbacks or curves in the road here!). Most folks won't put up with the look of twin antennas on their personal vehicles.
Thinking about another challenge for their lack of a good ground-plane is the boaters in the marine world. Fiberglass just does not work as a conductor for RF. You can certainly buy a Marine CB antenna but in my past experience they never did work very well. We tried these on RV's as well and folks were rarely satisfied.
The last desperate approach that we tried to facilitate a ground-plane was to create a square pattern out of conductive tape under a single antenna. You have to both physically and electrically have the antenna mount through the center of this surface. Actually I seem to remember talking someone into letting me mount a large piece of sheet metal on a roof once and it was so-so for results.
As I mentioned this was all a long time ago for me so you should see what the pros are up to these days. Who knows, maybe they've changed physics since my experience!
Lastly, if you are simply trying to communicate within a traveling convoy, you might be ok as-is. Just keep in mind that these are low-powered noisy radios that folks expect too much out of.
Good luck to you as I'm going 10-7...
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