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Antenna filter advice

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burnce

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I am having a problem with an AM radio that is squelches out whenever another radio keys. We can not move the antenna, we are required to use the preinstalled antenna mounts. Is there another solution that I can try, perhaps a filter that would keep everything above 125 MHz from hitting the antenna connection on the radio.
I am using an Icom A210 to rx/tx at 121.9 MHz and everything else in the higher bands.
Any help would be appreciated.
 

mmckenna

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That's called desense, and the way to deal with it is to move the antennas farther apart. Sounds like that isn't an option, though.

You can live with it. It's not going to hurt anything unless your antennas are way to close together.

You could try a filter, but I don't have any suggestions. The AM aircraft VHF band is close enough to the FM Broadcast band that you may impact that.
 

burnce

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It's not terrible but we're finding that the guys turn the radio off to avoid the squelch which for obvious reasons is no good. The antennas are 3 feet apart which I think is enough and unfortunately motor pool has forbidden us from drilling any holes so I'm stuck with the factory positions
 

mmckenna

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Ah, yeah, that could be a problem.

Some commercial radios like that can be programmed to turn on/off with vehicle ignition. Some will let yo program it to ignore the power switch. You can even program minimum volume levels to keep them from turning the radio volume down too far.
Not sure if that radio will support it though.
 

prcguy

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Is this on something like an airport fire vehicle where you have other radios in the 154Mhz range maybe for Weston FD? Is the 121.9Mhz frequency fixed and never changes? If so its possible to have a band pass filter made that only allows the 121.9 frequency pass through to the aircraft radio and it will severely attenuate signals from other radios in other bands. I probably have one of those in a drawer somewhere.

Its also possible to have a low pass filter made that would allow the entire VHF air band to pass to the aircraft radio but limit all frequencies above to allow you to change aircraft frequencies and at the same time keep other radios from bothering the aircraft radio.

If you were talking about an aircraft radio affecting the AM or FM broadcast radio in the vehicle, then that goes a different direction.
prcguy
 
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lmrtek

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if 121.9 is what you want to operate without desense then what you need is a bandpass filter

DCI makes vhf bandpass filters custom tuned to your frequency and they are very reasonably priced

1-800-563-5351
 
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