Vhf problem

mr mischief

mr mischief

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Hi all

I have a problem that’s been ongoing for a few weeks with the vhf radio

Basically it works fine on the rx side but has been reported that on tx it is readable but very quiet even over short distances and switched to 25 w

The vhf is a Raymarine 240 dsc built in unit

Not sure where to start I,m a bit reluctant to ditch it if it’s a simple fix

Graham
 
This in my experience is a common fault when the aerial or coax is damaged in some way. Start with replacing the co-ax and checking connections
 
If you have 12v USB chargers, un-plug all of them and test again.

If the above dose not solve the problem, then start to check the cables, aerial, ....etc.
 
peterjaw said:
If you have 12v USB chargers, un-plug all of them and test again.

If the above dose not solve the problem, then start to check the cables, aerial, ....etc.
Click to expand...
I’m fascinated to know why you think disconnecting any USB’s on the boat will improve VHF transmission.

On a more serious note.

I’d want to know whether the received signal is fully quietening the receivers of this who are in range. In other words is the received signal all hissy or is it silent except for a faint voice?

VHF uses frequency modulation and once you reach the threshold of the FM detector, increased power or signal level makes no difference to the volume of the audio. A strong enough signal reduces the white noise hiss to zero (hence the phrase, ‘fully quieting signal’. If the signal is strong enough, and the audio is still weak, then it’s a technical problem in the transmitter. (The obvious culprit might be the microphone and it’s lead as they’re vulnerable to damage)
If the signal in the receivers is hissy then it’s transmit power and the antenna and coax is the go to first place to look. (Although a power meter would help eliminate transmit problems).
 
Many thanks for the replies
I am down on the boat today and will investigate the coax cable to the aerial and disconnect the two plug in 12v chargers and see if that helps .

Graham
 
john_morris_uk said:
I’m fascinated to know why you think disconnecting any USB’s on the boat will improve VHF transmission.

On a more serious note.

I’d want to know whether the received signal is fully quietening the receivers of this who are in range. In other words is the received signal all hissy or is it silent except for a faint voice?

VHF uses frequency modulation and once you reach the threshold of the FM detector, increased power or signal level makes no difference to the volume of the audio. A strong enough signal reduces the white noise hiss to zero (hence the phrase, ‘fully quieting signal’. If the signal is strong enough, and the audio is still weak, then it’s a technical problem in the transmitter. (The obvious culprit might be the microphone and it’s lead as they’re vulnerable to damage)
If the signal in the receivers is hissy then it’s transmit power and the antenna and coax is the go to first place to look. (Although a power meter would help eliminate transmit problems).
Click to expand...


Apparently the received signal is very quiet but readable no mention of hiss from Solent coastguard
 
john_morris_uk said:
I’m fascinated to know why you think disconnecting any USB’s on the boat will improve VHF transmission.
Click to expand...
Hi John,
I am not expert in radio communication. But I have similar experience as described here.
At very first, I could not find out any potential problem, but just when my phone was fully charged and I un-plugged the 12V USB charger
everything went back to normal again. I realized that the charger might cause the problem. Then I did some tests by repeating plug and un-plug and found I can replicate the scenario.

From many posts in this forum seems indicate that some certain 12V USB chargers do cause problem to VHF communication, no matter cheap or expensive chargers.
 
peterjaw said:
Hi John,
I am not expert in radio communication. But I have similar experience as described here.
At very first, I could not find out any potential problem, but just when my phone was fully charged and I un-plugged the 12V USB charger
everything went back to normal again. I realized that the charger might cause the problem. Then I did some tests by repeating plug and un-plug and found I can replicate the scenario.

From many posts in this forum seems indicate that some certain 12V USB chargers do cause problem to VHF communication, no matter cheap or expensive chargers.
Click to expand...
Regrettably some USB chargers (and some other modern electronics) are prone to emitting all sorts of spurious transmissions, it would be a very poorly designed and constructed VHF that allowed such spurious emissions to interfere with transmit. Much more likely that they’d block the receiver.
 
I had this identical fault. It was caused by a fault in the cockpit mic connector where it plugged in. When I picked the mic up to talk, the movement disturbed the joint, and it would work sometimes or not. Rx unaffected obviously. Fix was a new mic and cable.

Might be worth checking if yours is similar.
 
I installed a vhf radio and had transmission problems. It was caused by a poor supply. It had enough power to receive but not transmit.
You may have a poor or corroded connection somewhere in the power supply.
 
Had similar. Mine was dropping volts as soon as transmitting due to the extra demand.
after rewiring the boat the last connection to be removed was from the ign key and was loose.
Might be worth putting a voltmeter on the VHF supply wires and transmitting to see a significant volt drop (I would expect normal use to drop about 0.5v
Just another thing easily eliminated

Edit, see above
 
My radio has the option to show voltage on the display with warnings if the battery voltage is too low (flashing batt symbol), that may help diagnose if the voltage drops on tx.
 
I disconnected all 12 v chargers , checked the coax for damage as best I could pulled various connections apart and it’s made not one jot of difference

I will investigate the wiring further , bit of nightmare tracing cables on boats tho

Can anyone recommend anyone in the hythe area that’s good on marine electrics

Luckily in the meantime I have the trusty handheld vhf
 
Rocksteadee said:
Had similar. Mine was dropping volts as soon as transmitting due to the extra demand.
after rewiring the boat the last connection to be removed was from the ign key and was loose.
Might be worth putting a voltmeter on the VHF supply wires and transmitting to see a significant volt drop (I would expect normal use to drop about 0.5v
Just another thing easily eliminated

Edit, see above
Click to expand...
This will confirm if you have a supply problem on the +ve rail or not.
 
I was always advised to wire the radio direct to the battery in case you ever needed to isolate the electrics (fire what have you) and still retain emergency comms.

(This is not said to start another forum argument but if the above is a power issue then this would be another reason for doing so)
 
BruceK said:
I was always advised to wire the radio direct to the battery in case you ever needed to isolate the electrics (fire what have you) and still retain emergency comms.

(This is not said to start another forum argument but if the above is a power issue then this would be another reason for doing so)
Click to expand...
Yep, mine's kinda like that, in it's via the main 12V domestic breaker but not switched separately.
 
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