VHF blowing fuse when transmitting

A

Anita Marie

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Oct 31, 2003
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C Dory Year
2005
C Dory Model
25 Cruiser
Vessel Name
Anita Marie
I kept blowing the 3 amp main fuse when I try to transmit on my VHF radio. When I replaced it at the dock it worked even at 25 watts. When we were underway it immediately blew again. I checked to make sure the antenna plug was tight.
What would be a good way to check that it was either the radio or antenna? Would just disconnecting the antenna be a good way?

Fred
 
I would not transmit without an antenna hooked up to the radio as I think I have heard not to do that. I think there is a meter called an swr meter for checking an antenna's condition. It goes inline inbetween the radio and the antenna. Usually bad antenna connections are the problem if the antenna does not appear to have physical damage. Also check the microphone cord for breaks or cracks. You could use a 12v battery to power your radio while connecting to another boaters antenna. That ought to tell you something.
D.D.
 
Hi Fred can you trace to where you pull power for the radio? It should be at a buss bar running as direct as possible to the battery. It may be that it is attached to the alternator charging post and could be seeing a spike over the fuse capacity
 
Although 3 amps theoretically is the "correct" size fuse, almost all VHF's use 5 to 6 amp fuses. There are reasons that the radio draws more than 3 amps at 25 watts. Try a 5 or 6 amp fuse. Although I agree that you should not transmit without an antenna, there are protective circuits which will shut down the final output transisters, and prevent damage.
 
A VSWR meter goes in between the transmitter and antenna. It has a switch in the middle, with two positions.

In the forward position it tells you how may watts you are transmitting, in the reverse it tells you how many watts are reflected back at the radio. Hopefully the answer to #2 is not much. A high reflected power indication points to a bad antenna or damaged coax.
 
Bob, I will try a bigger fuse. The radio has been working for 7 years with not problems. I was wondering, it has a device that allows the AM/FM radio to share the antenna when not transmitting. I believe it shunts the radio when you transmit. Could this be the culprit?
 
Yes, it is possible that this may increase the current draw. I try and avoid these combo antennas. I have seen a number of boats which come with the 3 amp fuse, and it blows--then a 5 amp works fiine.
 
I would check your ground connections . A loose one may increase current draw.
Marc
 
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