Question: radio vs radio interference in mobile

[lightningx54]

Background: I have a Jeep Cherokee with two mag mount antennas, one dual band vhf/uhf in the way front and a vhf in the way back. The front is for the Yaesu FT7800 and the backis connected to the Byonics Micro-Trak 10 watt APRS beacon...

What can I do to stop the APRS beacon from blowing out the Yaesu radio? Filters? Chokes? The antennas can't get any farther apart. I unplugging the beacon for now but what can I do? How do they get away with it on police cars and stuff? Usually I see 6 antennas grouped in a 1' by 1' square and they don't have problems.

 

[n5ims]

Background: I have a Jeep Cherokee with two mag mount antennas, one dual band vhf/uhf in the way front and a vhf in the way back. The front is for the Yaesu FT7800 and the backis connected to the Byonics Micro-Trak 10 watt APRS beacon...

What can I do to stop the APRS beacon from blowing out the Yaesu radio? Filters? Chokes? The antennas can't get any farther apart. I unplugging the beacon for now but what can I do? How do they get away with it on police cars and stuff? Usually I see 6 antennas grouped in a 1' by 1' square and they don't have problems.

Not a whole lot you can do about it. When one radio transmits, it will overload the front end of the other radio(s) that are on the same band.

Those multiple antennas you see very close together on a PD vehicle are not for transmit, but are an array of antennas used to track stolen cars or bags of money stolen in a bank robbery. They are generally in a square (4 antennas) or triangle (3 antennas) and go to specialized radios that display the strength and direction from the patrol car that the stolen bank loot or LoJack equipped stolen car is. Since this is a receive-only application, they work just fine that close together. In fact, they're placed in specific locations relative to each other so the circuits can determine the signal's direction. If that agency uses a VHF-Hi frequency, the tracking device will also overload when they transmit but once they release the mic button will pick up and track the signal again.

 

[kayn1n32008]

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The only way. Would be to use a band pass filter to notch out the APRS transmitter.

Another possibility is to use LMR gear, or try and use UHF as much as possible. I had a 5w tracker, and it would wipe out my 8800. I just started to use UHF when I could.

 

[jim202]

Background: I have a Jeep Cherokee with two mag mount antennas, one dual band vhf/uhf in the way front and a vhf in the way back. The front is for the Yaesu FT7800 and the backis connected to the Byonics Micro-Trak 10 watt APRS beacon...

What can I do to stop the APRS beacon from blowing out the Yaesu radio? Filters? Chokes? The antennas can't get any farther apart. I unplugging the beacon for now but what can I do? How do they get away with it on police cars and stuff? Usually I see 6 antennas grouped in a 1' by 1' square and they don't have problems.

One trick that has been used for many years is to put a pair of back to back hot carrier diodes from the input to the first RF amp to ground. Make sure there is a series resistor between the antenna connector and the diodes. I also like to see a coupling cap just before the diodes. You might also need a second cap between the diodes and the gate or base of the RF amp to prevent changing the DC bias to the RF amp.

 

[lightningx54]

Isn't overloading the front end bad?

 

[lightningx54]

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The only way. Would be to use a band pass filter to notch out the APRS transmitter.

Another possibility is to use LMR gear, or try and use UHF as much as possible. I had a 5w tracker, and it would wipe out my 8800. I just started to use UHF when I could.

What would be different with using Land-Mobile radios?

 

[AK9R]

The only way. Would be to use a band pass filter to notch out the APRS transmitter.

The standard APRS frequency is 144.390 and the frequencies for FM voice repeaters start at 145.110. A repeater on 145.110 is most likely using an input frequency of 144.610. Therefore, if you could get a high pass filter tuned somewhere between 144.390 and 144.610, you might be able to filter out the APRS beacons from the voice radio. Unfortunately, it's still going to require a pretty sharp filter.

 

[kayn1n32008]

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Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9900; en-US) AppleWebKit/534.11+ (KHTML, like Gecko) Version/7.1.0.1047 Mobile Safari/534.11+)

The only way. Would be to use a band pass filter to notch out the APRS transmitter.

Another possibility is to use LMR gear, or try and use UHF as much as possible. I had a 5w tracker, and it would wipe out my 8800. I just started to use UHF when I could.

What would be different with using Land-Mobile radios?

Much more selective receivers.