Troubleshoot VHF please.

[Jon magowan]

Ten year old Garmin VHF 200i.

AIS seems to be transmitting normally.

Radio receiving normally ( hearing coast guard routine transmissions)

Transmitting only to a short range (1 to 2 miles).

High power selected and indications on display are correct and normal.

Where does the trouble lie?

I’m guessing the aerial is ok since AIS appears to be ok.

I’m guessing the box itself is operating ok since it is actually transmitting and receiving ok.

I’m thinking of changing the aerial and cable anyway, as a first step.

Anyone have any bright ideas? All advice gratefully received. Electronics are clearly not my thing !

 

[wonkywinch]

Ten year old Garmin VHF 200i.

AIS seems to be transmitting normally.

Radio receiving normally ( hearing coast guard routine transmissions)

Transmitting only to a short range (1 to 2 miles).

High power selected and indications on display are correct and normal.

Where does the trouble lie?

I’m guessing the aerial is ok since AIS appears to be ok.

I’m guessing the box itself is operating ok since it is actually transmitting and receiving ok.

I’m thinking of changing the aerial and cable anyway, as a first step.

Anyone have any bright ideas? All advice gratefully received. Electronics are clearly not my thing !

I had a quick look at the manual, this unit doesn't have AIS so that must be a separate unit in your boat and probably wired to the antenna through a automatic switching unit. As you say, it works but both VHF and AIS can receive almost on an old piece of wet string whereas transmitting requires a good antenna and connection.

I would check the antenna connections carefully, reconnecting using silicone grease. Trace the antenna cable run all the way from the back of the set to the antenna and check all connections, look also for any damage to the cable.

If it was working once then deteriorated, my money is on a dirty/wet antenna connection at the aerial.

Is the battery voltage OK, can you measure it at the radio and check it doesn't drop when the microphone is keyed (ie pressed to transmit).

 

[mikegunn]

Ten year old Garmin VHF 200i.

AIS seems to be transmitting normally.

Radio receiving normally ( hearing coast guard routine transmissions)

Transmitting only to a short range (1 to 2 miles).

High power selected and indications on display are correct and normal.

Where does the trouble lie?

I’m guessing the aerial is ok since AIS appears to be ok.

I’m guessing the box itself is operating ok since it is actually transmitting and receiving ok.

I’m thinking of changing the aerial and cable anyway, as a first step.

Anyone have any bright ideas? All advice gratefully received. Electronics are clearly not my thing !

Check the fuse holder in the 12V supply to the radio.
Some years ago I had a similar problem with an Icom VHF radio. I spent hours attempting to trouble shoot the problem and even replaced the aerial and lead. All to no avail and eventually returned the set to Icom for analysis. They found nothing wrong.
I then discussed the matter with a member of their support department. They suggested that I look very carefully at the supply fuse and its fuse holder. It was explained to me that when the PTT button is pressed there is a surge of current which could be as high as 20 Amps. Apparently this momentary passage of a high current can cause arcing between the fuse and its holder resulting in a high electrical resistance. This resistance effectively significantly reduces the output to the aerial. It won’t affect reception, only transmission.
To complete my story I followed the guidance given by Icom and did indeed discover that the supply fuse was not firmly located against its contacts in its fuse holder. I changed it out for a holder with better contacts and was immediately able to call ships at the theoretical limit of range.
Of course it’s not only the fuse/holder that can cause this phenomenon but any connection in the electrical supply where there is a connection. However, I was assured that fuse holders have remained a prime suspect where such symptoms are observed.
Mike

 

[Boathook]

When my VHF wouldn't transmit the aerial had corroded inside also causing the wire to corrode. It always received well though.

 

[Supertramp]

+1 for checking the aerial.

A few weeks ago while out for a sail I noticed my masthead VHF aerial had disappeared (blown off!). Everything appeared normal although the VHF was strangely quiet and my AIS was not receiving targets. A check on Marine Traffic showed no position.

All fixed with a replacement aerial.