BCD996P2: Overloading scanner with nearby 2M/70CM mobile radio?

V_A_R_I_A_B_L_E

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I have a mobile dual band radio capable of anywhere from 5-50 watts, with a permanent roof-mounted NMO antenna near the rear of the roof of my SUV. About 4ft away near the front of the SUV, closer to the top of the windshield, I have a mag-mount NMO antenna connected to my 996P2... I noticed while tuned to a constant broadcast frequency in the 450Mhz range, and transmitting with the dual bander in the 440 range (I believe I was first at 50 watts, and then it still happened at 25 watts), the scanner audio cut out for the duration of the transmission, and came back as soon as I un-keyed my mic.

My question is, if I replace that mag-mount with a 2nd permanent NMO hole for my scanner antenna and run this as my setup, will I risk damaging the scanner every time I transmit? Is this effect of apparent overloading due to the proximity of the two veritcal antennas perfectly acceptable to repeat/allow for longer tx durations, or is it evidence of what will eventually amount to cumulative damage? I'd like to know before I drill. Thanks!

Bonus question: I'm also considering including a CB antenna halfway between the two existing antennas, 2ft from the front antenna and 2ft from the rear antenna, a total 4ft spread for all three (I was going for max distance between similar freq antennas)...considering the much larger frequency gap, do I have anything to worry about with regard to once again overloading the scanner or any other general antenna proximity considerations?
 

letarotor

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With the antennas that close together, and would you transmitting it 25+ watts, you're going to run into this problem over and over again on the scanner. It may not be such a problem for the CB since it's completely in a different band, the HF frequency ranges. I've had the same problem at my home and the only thing that will help you from overloading the front end on the scanner is a horizontal distance between the antennas. I have to have about a 30-ft separation. The vertical distance can also make a difference but on a vehicle you really have no way to separate the antennas far enough.

There are items sold and I cannot remember what the limiter is called. But if you look at Stridsberg based out of Shreveport, Louisiana, they sell a limiter which may help you. A friend of mine just bought one recently and even though it did not wipe away his problem in the 220 MHz band when he transmitted, he was able to do a little moving around of his antennas and clear up the problem and the limiter was in line to help prevent signal overload. I can't speak as to whether or not it's going to damage the radio over time. I'm worried about the same thing myself but thankfully I put enough separation between my antennas where this seldom happens unless I transmit on the dual band antenn a I have mounted in the front portion of my house where there are two antennas, one a 9-ft collar linear antenna for the dual band frequencies and the other a disc going antenna for the SDS100, and it does cause the same issue still because these antennas are both mounted on the same mast. I just usually put on the rubber ducky Remtronix antenna If I'm going to be transmitting on that specific mast and I'll make sure that the Stridsberg multi-coupler hooked up to a few scanners in that part of the house Is either unplugged from the other radios it goes to or I just make sure those radios are turned off.

It's a royal pain in the rear having to figure out what will and won't work. But I do have to wonder myself how much damage this might cause with the front end overload on the scanners? Maybe somebody else will have more knowledge or other ideas that might help? But I'm afraid the problem with the antennas being so close together is going to remain and you may just have to turn off the scanner when you want to talk on the ham radio unfortunately. I'm interested to see what other replies people have also here. Good luck...

Brian (COMMSCAN)

Sent using Google Voice to text. Please excuse any errors I may have missed due to my vision problems.
 

V_A_R_I_A_B_L_E

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Thanks Brian. Ultimately I'm fine having to live with the tx overload in the sense of my scanner being temporarily useless while transmitting (especially since it's a vehicle roof I only have so much space to play with) but my main concern really is just not wanting to inadvertently damage anything. Beyond that, tips/tricks/best practices/common conventions are welcome, as this is my first mobile multi-antenna install.
 

letarotor

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Thanks Brian. Ultimately I'm fine having to live with the tx overload in the sense of my scanner being temporarily useless while transmitting (especially since it's a vehicle roof I only have so much space to play with) but my main concern really is just not wanting to inadvertently damage anything. Beyond that, tips/tricks/best practices/common conventions are welcome, as this is my first mobile multi-antenna install.
Yeah I understand and I'm interested also when seeing what others may say about the damage that may or may not occur. That's the one thing I never really have had a clear answer on.once again, good luck and I'm going to keep a look on any other replies myself :)

Brian
 

RichardKramer

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I have a Hyudai Sante Fe. On the roof are 4 antennas and one antenna in either side of the rear hatch door. The antennas from front to back on the roof: Larsen tri band scanner, Antenna Specialists dual band scanner, CB, 10mtr ham antenna; on the hatchback: driver side is a 6mtr whip; on the passenger side a wide band vhf/uhf ham antenna. I do get some rfi on my 436 and 396XT scanner running 50 watts on my Yaesu FT8900 quad band (10mtr/6mtr/2mtr/440) ham radio when tx on some ham freqs. Never had any damage to the scanners and have been using this set up for over 3 years. I don't recall having any rfi on the CB, even on SSB running 12 watts.

Rich - N3VMY - KAG0096
 
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