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Old 05-17-2011, 10:26 AM
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Default Safe separation distance on mobile antennas

I am installing a new Cobra 29XL CB (haven't used one since the '70's) as well as a BCT15 and a BCD996 in my '05 Ford Excursion and am concerned about antenna separation. I have a decent amount of roof area to work with but a rooftop air deflector will be taking up about 30" of the rear section. I should be able to leave just enough room to stick the CB's mag mount at the very rear edge of the roof behind the air deflector as long as that position won't be a problem ground plane wise. In the rearmost position I'm pretty sure I'll have good enough separation to avoid any issues with the scanners. But if the rear position and it's less than ideal ground plane situation will cause me performance issues with tx/rx I will need to move that CB antenna a lot closer to the scanner ants. How far do I need to keep them apart to prevent any harm to the scanners?
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Old 05-17-2011, 11:13 AM
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As long as the separation is 3-4 feet and you are using a stock 4 Watt CB radio, no RF amplifiers, you shouldn't have any problems. If you are running an amplifier then make sure that the separation is 6 feet plus or ground the scanner antennas with a switch when talking on a high powered CB radio.
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Old 05-17-2011, 12:10 PM
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The theoretical answer is a quarter wave, which at 27 mHz is 8.67 feet, so the practical answer is to get the antennas as far apart as possible on the top of the vehicle.
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Old 05-17-2011, 1:29 PM
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LOL, I actually have more than 8.67 feet on this monster's roof! I just don't want to have the scanner ants all the way up near the windshield. But I will try to keep them as far forward as I can and keeping it looking "normal".
Does the placement of the CB's antenna at the very rear edge of the roof, with metal on only 3 sides sound workable? The unit will be used mainly for traffic/weather warnings and chatting back/forth with travelling buddies on camping trips.
Thanks for the help guys!
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Old 05-18-2011, 7:18 AM
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Having less of a ground plane in one quadrant will skew the transmit signal pattern somewhat but probably not enough to matter very much..
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Old 05-21-2011, 8:09 PM
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Thanks, the radio shop I bought the Wilson1000 from includes a SWR check with the purchase. At my rear edge location it wasn't so good, moved foreward a little bit was much better, of coarse centered it was best. I have to put the scanner antennas somewhere, so I'll have to accept a little performance on the CB and slide the mount onto the rear portion.
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"Police are putting CHOP STICKS in the road?" Gotta love her!

Tri-State live feed http://delaware.pa.scanamerica.us/index.php
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