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.

 

[Jon magowan]

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

Thanks Mike, for taking the trouble to explain your situation.
I would not have considered that at any point !

 

[oilybilge]

Buy an emergency aerial. They're useful for emergencies, but also handy for this sort of situation.

I always thought I got 'good enough' reception with my masthead aerial until I plugged in the emergency aerial and got better. Turned out the coax cable was all corroded above the deck connector.

 

[wonkywinch]

Thanks Mike, for taking the trouble to explain your situation.
I would not have considered that at any point !

My tip in post #2 "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)" would pick this up as well as several other reasons why the supply voltage falls when the (high power demand) transmitter is keyed.

As well as the fuse, there could be other corroded or loose connectors, a damaged wire, weak battery, loose negative connection. Checking volts at the 12v supply on the back of the set is one of the basic checks to be carried out.

 

[William_H]

Do make sure that the level of voice when your transmitter is received is similar to other stations. Microphone may be bad. But probably antenna as said. ol'will

 

[noelex]

SWR meters are not expensive these days. See if you can borrow one.

Most problems are aerial/coax/or connections related so this should be this first check.

 

[Martin_J]

Whereabouts are you based?

It would only take two minutes with the right SWR/Power meter to check both the transmit carrier power of the VHF radio and the quality of the antenna system..

As noelex says, there might just be someone nearby with the correct test kit.

 

[Martin_J]

The link below is to a short, 23 second video (on OneDrive) that I made showing measurements of forward power, reflected power, then a calibration (to top end of the scale) and finally an SWR reading.

It doesn't take long and the handheld was being used to test out the antenna system without having to touch the installed VHF. (Useful if you want to test from the connector at the bottom of the mast for example).

https://1drv.ms/ Video showing forward power, reflected power, calibration and then the SWR test.

 

[wonkywinch]

The link below is to a short, 23 second video (on OneDrive) that I made showing measurements of forward power, reflected power, then a calibration (to top end of the scale) and finally an SWR reading.

It doesn't take long and the handheld was being used to test out the antenna system without having to touch the installed VHF. (Useful if you want to test from the connector at the bottom of the mast for example).

https://1drv.ms/ Video showing forward power, reflected power, calibration and then the SWR test.

Top marks for not dumping a carrier test on CH16

 

[oldgit]

Had similar problem some while ago ?
After considerable faffing it turned out the automatic switching device for the AIS/VHF radio had failed.
Never really got to bottom of it.
Choice was a new DY switching unit at £300 or a separate aerial for AIS at £50.00.
Connected VHF radio direct to existing aerial and AIS unit to new aerial.
Job done.