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Old 03-31-2019, 04:12 PM   #1
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VHF transmit causing stereo radio to turn off

Whenever I transmit on my VHF radio it causes my stereo radio (both satellite radio and terrestrial radio) to turn off. It only does this while transmitting at 25 watts, while on 1 watt all is ok. So the VHF transmission is causing my audio radio to somehow overload and shut down.

How do I shield the audio radio from the vhf signal? Is there some sort of filter I can purchase to alleviate this problem?
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Old 03-31-2019, 04:16 PM   #2
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Sounds like Voltage drop. Wiring is too small to support the other two devices while the VHF is drawing power to transmit. Upsize your wiring (both negative and positive) from the breaker panel to your radios. Make sure your ground/negative are clean and have a good connection.
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Old 03-31-2019, 04:28 PM   #3
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Sounds like Voltage drop. Wiring is too small to support the other two devices while the VHF is drawing power to transmit. Upsize your wiring (both negative and positive) from the breaker panel to your radios. Make sure your ground/negative are clean and have a good connection.
Voltage drop on the audio radio? My helm has a subpanel with all navigation equipment and lights. The VHF radio and audio radio are on separate circuits. My chart plotter which consumes a lot more amps than an audio radio isnít effected. I guess to test your theory I could connect a voltmeter to my audio radio power wires and press the vhf transmit and see if the voltage drops significantly. Will give that a go. Thanks
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Old 03-31-2019, 04:35 PM   #4
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I didnít realize they were on separate circuits. Still sounds like voltage drop though. It would be your VHF when on full transmit that would be pulling things down. I would think it would pull more power than your chart plotter, but could be wrong. Does it do the same regardless of everything else on that sub panel on versus off?

Interference wonít shut down most radios. But if you are getting interference, make sure all three radios are well grounded to the chassis. Then baluns on the power feeds or RF choke filters could be considered/added.

If it was me Iíd check the power and voltage drop potential first though.
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Old 03-31-2019, 05:34 PM   #5
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I'm about to pull the trigger on a bunch of ferrite suggestions, but first:
How far away is the VHF antenna from the affected device, and the power and speaker wiring from the affected device? And, what is the make/model of the problem child? Since you have a FRP boat, things like the pilothouse roof are virtually RF transparent.
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Old 03-31-2019, 05:46 PM   #6
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Whenever I transmit on my VHF radio it causes my stereo radio (both satellite radio and terrestrial radio) to turn off. It only does this while transmitting at 25 watts, while on 1 watt all is ok. So the VHF transmission is causing my audio radio to somehow overload and shut down.

How do I shield the audio radio from the vhf signal? Is there some sort of filter I can purchase to alleviate this problem?

Avalanche is on the right track. At 25 watts transmit, the VHF radio is drawing a lot of current. If your other radios are sharing the same current source, they will power cycle because of the voltage drop.


I have seen this MANY times.


1) Look at the size and length of the wires that feed this circuit, positive and the ground.

2) Measure the voltage at either of the radios that are shutting down while hitting the transmit key at 25w on the vhf.


I'd be willing to bet the supply is dropping very low when you key the mic...
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Old 03-31-2019, 05:48 PM   #7
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Voltage drop on the audio radio? My helm has a subpanel with all navigation equipment and lights. The VHF radio and audio radio are on separate circuits. My chart plotter which consumes a lot more amps than an audio radio isnít effected. I guess to test your theory I could connect a voltmeter to my audio radio power wires and press the vhf transmit and see if the voltage drops significantly. Will give that a go. Thanks

Doesn't matter if they are on separate 'feed' circuits, if they share the same ground wire.


I'm still betting on voltage drop.
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Old 03-31-2019, 05:52 PM   #8
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Voltage drop on the audio radio? My helm has a subpanel with all navigation equipment and lights. The VHF radio and audio radio are on separate circuits. My chart plotter which consumes a lot more amps than an audio radio isn’t effected. I guess to test your theory I could connect a voltmeter to my audio radio power wires and press the vhf transmit and see if the voltage drops significantly. Will give that a go. Thanks

Re: "My chart plotter which consumes a lot more amps than an audio radio isn’t effected."


Your chart plotter (being a very expensive and critical navigation device) is engineered to withstand large voltage fluctuations. Your entertainment systems? Not so much.
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Old 03-31-2019, 06:04 PM   #9
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I agree that I would check power first. Check grounds second and also for loose or corroded connections.
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Old 03-31-2019, 06:19 PM   #10
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I'm about to pull the trigger on a bunch of ferrite suggestions, but first:
How far away is the VHF antenna from the affected device, and the power and speaker wiring from the affected device? And, what is the make/model of the problem child? Since you have a FRP boat, things like the pilothouse roof are virtually RF transparent.
Iíd estimate the tip of the vhf antennae is about 25 feet from the roof of the pilot house which is where the satellite radio and am/fm radio antennae reside. The radio is a generic Kenwood automobile radio.
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Old 03-31-2019, 06:23 PM   #11
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25í hmmm. Thats a pretty goodly distance. The dvV measurements would be easy and first on the list. Let us know. I specialize on the rf stuff, but only when needed
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Old 04-02-2019, 10:25 AM   #12
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Thanks for all the inputs. Upon investigation appears there was a loose connection near the radio. New butt connections solved the problem. Thanks again for all the valuable inputs.
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