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Old 11-14-2013, 3:29 AM
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Default VHF CDM1250 cutting out FM Stereo

Last night when I keyed up my VHF CDM1250, my FM stereo was playing at the same time and cut out when I keyed up. It resumed when I took my finger off the PTT. I don't believe it was a power issue, as none of the other components in my vehicle dimmed/faded/etc, and the stereo did not cut out when in "aux" or CD mode. Could it be the frequencies interfering with each other? The radio also cuts out my scanner when I key up.

Any help is appreciated. Thanks!
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Old 11-14-2013, 5:23 AM
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The transmitted RF is overloading the receivers. Not unheard of, even with good antenna separation on a vehicle. Basically there is enough energy being picked up by your FM radio and scanner to overpower everything else it's hearing, even though they are not on the same frequency.
Poor receiver filtering will let this happen, but so will having antennas to close together.

Just make sure your transmit antenna isn't too close to the scanner or broadcast radio antennas. 1/4 wave length at minimum, but more is better.
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Old 11-15-2013, 11:00 AM
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High SWR could also be a problem....
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Old 11-15-2013, 4:39 PM
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I'd say it's more due to the proximity of your VHF transmitter to your FM antenna, and the overall lower quality of FM receiver front ends today.

On my old 2005 Elantra, the factory radio was excellent at receive sensitivity and did not care about the Larsen NMO 2/70 and a 50 watt 2 meter signal 2 feet away.

When I replaced it with a JVC (then Kenwood) aftermarket radio, both would suffer severe desense when I keyed up on 2 meters. The Kenwood had HD, and the HD would always drop out when I keyed up the VHF side of my dual band, and analog signals would become weak or become total static. Same antennas and same feedlines.

I have yet to install a transceiver in my new 2013, but I am concerned as all the on board electronics, TPMS (which uses 430MHz transponders on each wheel), navigation system- and more importantly, the AM/FM antenna is actually in the rear windshield. It also has an active antenna amplifier, and the last thing I want to do is blow it out with excessive RF.

today's consumer cars are not very "radio" friendly places.
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Old 11-16-2013, 2:05 AM
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SWR would not be an issue. RF is RF, whether it is a good match or not for the radio. The front ends of the consumer radios are being swamped by the RF.

Welcome to cheap Chinese crap radios. And MTS2000 has a point. Prolonged transmissions on one or both of the UHF 110w XTL5000s in my vehicle cause the TPMS to alert, and I also worry about the preamp in the antenna line.

I suppose I should do something about it, before I put the kilowatt Micom in there, but so far the 330watt VHF hasn't bothered the preamp.

Fingers crossed.......
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