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Old 17-02-2011, 21:03   #1
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Radio Magic

I installed a new VHF in my boat, plugged the existing antenna cable in, and nothing - I can't get weather. The terminal end on the coax was looking a little scuzzy, so I replaced it - still nothing. While screwing around, thinking perhaps I'd mucked something up, I discovered that if I unscrew the connector and leave the center pin in the radio (whilst holding everything JUST RIGHT) I can receive. I haven't tried to transmit. I assume there's something goofy at the top of the mast, which I haven't been up yet. Any thoughts about what I should be looking for? The coax shielding chafed and grounding? Fried antenna? Something else? Is there a way to test the wire? Replacing it would be a real trick without pulling the stick and whatever the heck the wire inside the cabin is hiding behind, but I need a functional radio. HELP!
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Old 17-02-2011, 21:39   #2
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The antenna at the top of the mast lives in the second toughest environment. The first being the prop. You can be sure there is a problem at the top of the mast.

30 inches of any old wire stuck in the VHF antenna connector will prove that all is okay with the transceiver.
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Old 17-02-2011, 22:39   #3
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Did you check to see if your coax connector was okay?...the hot is not grounded? Is it the solder type?
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Old 17-02-2011, 22:51   #4
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The coax (radio end) is, as far as I can tell, OK, and my multimeter shows no continuity between the core wire and the shielding or core and connector nut.
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Old 18-02-2011, 06:38   #5
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How old is your antenna, and what brand of antenna do you currently have on it? Could just be that your wires at the antenna are loose or dry rotted from constant salt and sun.

Keith
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Old 18-02-2011, 07:02   #6
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Either a short circuit or open circuit can cause the symptom you describe of only being able to receive with the center pin connected. Since you've already checked for continuity and have none, assume an open circuit. In this situation, the outer coax shield is picking up the signal and being coupled to the center conductor when you have the shield disconnected at the radio. You should not try transmitting until you get the problem fixed. What model antenna do you have? Most are DC grounded and would normally show a short circuit during a continuity test. Is there a connection at the mast step? If so, check those connectors first.

Eric
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Old 23-02-2011, 10:55   #7
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Re: Radio Magic

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Originally Posted by Dustymc View Post
The coax (radio end) is, as far as I can tell, OK, and my multimeter shows no continuity between the core wire and the shielding or core and connector nut.
DC continuity proves nothing in an RF system - you may have a design which requires continuity through a coil.
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Old 23-02-2011, 12:06   #8
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Re: Radio Magic

Continuity tests in this situation are very useful if you know what your doing and know how to interpret the results. He's already been informed about the likelihood of having a dc grounded antenna.

Eric
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