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Old 30-06-2009, 09:58   #1
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WTF - Radio Powered w/ Neg Disconnected

Hi all;

One of my weekend projects was to replace the VHF coax inside the boat. When I did so, I fired up the radio, and it powered, but no sound came out. All operations looked normal, but no sound. Transmitted fine too. THe radio is less than a year old.

So later, I am doing project # 2, which is relocating the CD stereo player. In hooking up the power leads, I disconnected the negative return lead to the VHF, and Huh, it was still powered.

How can this happen? Could the no sound out of radio be related?

I brought the radio home and will try connecting it to a battery outside of the boat to see what happens. Strange things are afoot!

Chris
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Old 30-06-2009, 11:38   #2
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It sounds like you have a grounding fault. The VHF is probably grounded either through it's chassis or through the screen on the antenna.
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Old 30-06-2009, 12:19   #3
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That was what I was thinking. What are the implications of this?

The entire antenna system is new - new RG8x down the mast, through a cable clam into the boat, where it is barrel connected with the length going into a older switch. It switches from the main to an emergency stub antenna that is directly attached to the switch. It also splits to a FM antenna feed for the am/fm radio.


How can I test for this safely, and where should I start?

Chris
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Old 30-06-2009, 12:21   #4
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I believe Hampus is correct. When you get it home test it from an ungrounded surface. I am guessing it will not work (or rather will work as you expect)

Now ground the chassis and it will work. This is a common solution to avoid issues where people incorrectly ground - it should not be necessary but today most things are built to avoid support calls
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Old 30-06-2009, 12:33   #5
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So you are saying that the radio has circuitry that "Mutes" the audio output when there is a grounding issue? The chassis was never grounded, I just disconnected the - 12v wire, and it remained powered up (but no audio output). When in the mounted position, the radio is isolated, the mount does not connect to any metal.

Chris
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Old 30-06-2009, 12:42   #6
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Chris,

Do the tests at home. Stick a piece of wire into the center conductor of the SO-239 UHF connector on the back of the radio. That should be sufficient to receive WX broadcasts. Verify that it's working correctly. Don't worry about the ground issue.

On the boat, personally, I'd lose the two switches. Coax switches all have losses, even when they're working right. Often, they're not, especially with the cheaper ones. You don't need an antenna switch anyway to choose an emergency antenna; it's easy enough to connect one directly to the radio if/when you actually need it.

Get a real AM/FM antenna. Shakespeare makes one; West Marine and others have them.

Run an unbroken length of RG-8X from the connector at the base of your mast to the radio.

I don't know if you have a separate ground wire connected to the VHF, but it really isn't a great idea to have one even if the manufacturer recommends it.

Bill
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Old 30-06-2009, 13:04   #7
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I bet that if you disconnect the fm/am antenna from the switch, the VHF will die. If the switch is passive that is, without amplification and a power feed.

Turn down the squelch and turn up the volume on the VHF, if you still don't get any sound (noise), I'd suspet the speaker. Try connecting an external speaker to verify. Most new VHF radios have a standard speaker output.
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Old 30-06-2009, 14:32   #8
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The VHF is probably grounded at the antenna mounting at the top of the mast.

Steve B.
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