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spacing question

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emd001

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Oct 28, 2007
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Conroe, Texas
Hey all,
So school lets out next week and its time for me to finish my truck before summer school starts. So i have a question in regards to my antennas. So im planning on mounting 3 NMO antennas on the roof of my single cab dodge ram. 2 of the antennas are 800mhz for my scanners and the 3rd will be a comet sbb-7nmo for my yaesu ft8800. I plan on mounting the comet center of the roof, maybe a bit forward, and the two scanner antennas back corners (about an inch from each edge). Would this spacing be sufficient? i can get some measurements tonight if that will help. Also there will be a cb antenna on the toolbox and a satellite radio antenna on the roof, will any of these interfere with each other? Are there other paramters im not thinking of? this is going to be my first big install, thanks for any advice.
 

popnokick

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I don't think you have much to be concerned about. That is until you key up the FT-8800 or the CB. Receiver front end overload (on the radios not transmitting) will start making things interesting. But if you are simply receiving all the time (that's no fun), probably the worst you have to worry about is the IF stages of the various receivers picking up the signal(s) from the other receiver IFs. It will sound like a carrier with no modulation, and you'll find it only happens when the right combination of frequencies is selected on the receivers involved. I've had it happen on my scanner and my FM broadcast receiver. If the FM is tuned to the right station, the scanner will lock on a specific freq, likely related to the sum/difference relationship in the first IF. I don't think a pickup truck is big enough to get the radios and antennas far enough away from each other to do you any good. So get some ferrite wraparound filters and be ready.
 

SAR923

Active Member
Joined
Dec 19, 2002
Messages
1,511
I'd put the two scanner antennas closer than one inch from the edge of the roof for a better ground plane. I don't think spacing will be critical. Our radio techs set our system so that transmitting on one radio automatically cut power to the other radios to prevent any front end overload problems. That might be an option if you get interference between radios.
 
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