VHF

[uforea]

I have a Standard Horizon 1500 GX? radio which is just 18 months old and has worked very well until last week end when it would not transmit.
Initially the voltage to the set was very low( 10.93 volts) when the PTT was used and I have since replaced all the wiring and switches etc and now I get (11.90 )volts when the PTT is pressed and voltage at the batteries is 12.65 and starts the engine easily.
I get good clear reception and have tried the aerial from the AIS set but still no transmission.
What next?
Ted

 

[lenseman]

Hello Ted - Sorry about your VHF radio.

These things are difficult to diagnose from a distance but a number of things give a few clues.

You stated that it receives very well, this tells me straight away that the antenna is almost certainly OK and not faulty and you need to look elsewhere for any fault.

It is unusual for a transmitter to just suddenly fail without any other mitigating cause like transmitting into an open circuit. I am not saying it doesn't happen, but it is quite rare. /forums/images/graemlins/confused.gif

Low voltage to the VHF transceiver, Mmmmm, interesting? Did you measure the voltage at the input terminals (+ve and -ve) of the VHF set? You can sometimes get what is known as HR (high-resistance) and it occurs when you suddenly increase the load current (during transmit). What happens is terminals get warm / hot and if there are two dissimilar metals involved plus damp you sometimes get oxidising and then the terminals will not allow the required amount of current to flow and hence no transmit. After you stop transmitting, the terminals / leads can sometimes recover after a few milliseconds and allow a small amount of current to flow and your VHF receiver circuits to work.

On transmit, your radio might be drawing 6 to 8 Amps (notwithstanding the initial in-rush current) and on VHF receive it might be as little as 200 milliAmps mainly for the audio circuits.

Did you notice, perchance, whether the receiver was able to return to receive mode 'IMMEDIATELY' you stopped trying to transmit?

You really need to momentarily key up the PTT for about a quarter of a second whilst you are receiving a non urgent transmission from another station. As you let go the PTT can you then hear the distance transmission straight away. The distant transmission could be a friend on an nearby yacht on Channel xx doing a routine count from one to ten and back.

If it takes a noticeable amount of time to go into receive mode, there is a possibility that you are suffering HR in the DC supply leads and this will need to be addressed.

Those are really the only things you can do without a RF Watt meter, VSWR meter or a spectrum analyser. You could try measuring the DC current in the leads during transmit but you would need a DC current meter which can measure at least 10Amps.

Failing that, send it back to where you purchased it, crying in your beer, stating it is only 10 months old. Better still get your wife (XYL) to do the sob story she might get a better response.

You could always give it to me of course and buy yourself a new set. /forums/images/graemlins/grin.gif

 

[William_H]

Modern VHF sets carry all sorts of options and gizmos not necessarily important but put in because they can with the flexibilty of a microprocessor.
Eg different power levels different frequencies for transmit and receive (duplex) different in UK(world) to USA. maybe even a PA option.
All these options make it easy to make a mistake in managing the radio. I would suggest get the instruction book and check all the options and controls before you send it for repair. olewill

 

[Walusotu]

Last season I also had a problem with my relatively new VHF.
I could receive normally. I could transmit on low power but when on high the radio cut-out occasionally. Also when transmitting I measured a significant voltage drop when pressing the transmit button indicating a potential connection problem.

After a period of frustration and various checks I discovered a faulty circuit breaker!! Maybe worth checking all connections again.

Good luck