VHF signal not good.

[steveeasy]

On my recent Trip heading North I’d re installed my SH GX 1400 vhf radio. It had recently been to SH for screen repair.
I’d fitted new connectors so thought it wise to do a radio check. Over the course of 3 days I made a few calls for a radio check. Surprise no responses. A quick call to coast guard and they confirmed they had recieved the call and responded.
Over the following week no boats were seen on the water at all apart from a worrying Navel frigate and US Navy search on the VHF.
So how can I test the radio. I’ve two antennas and both seamed to make no difference. I’ve brought the radio back. Should I buy a meter ?.
Oh forgot to add I forgot to attach the ferrite ring thingy and the AIS signal seamed poor too.
Any thoughts other than starting with new bits.
Steveeasy

 

[Plum]

On my recent Trip heading North I’d re installed my SH GX 1400 vhf radio. It had recently been to SH for screen repair.
I’d fitted new connectors so thought it wise to do a radio check. Over the course of 3 days I made a few calls for a radio check. Surprise no responses. A quick call to coast guard and they confirmed they had recieved the call and responded.
Over the following week no boats were seen on the water at all apart from a worrying Navel frigate and US Navy search on the VHF.
So how can I test the radio. I’ve two antennas and both seamed to make no difference. I’ve brought the radio back. Should I buy a meter ?.
Oh forgot to add I forgot to attach the ferrite ring thingy and the AIS signal seamed poor too.
Any thoughts other than starting with new bits.
Steveeasy

I had the same problem with my SH GX1700 vhf, would transmit but not receive, and after talking to a very helpful person at SH and some trials found the cause. It was a 12v usb charger plugged in to a cigarette lighter socket. Spoke to the SH man again and he confirmed that a certain component in the vhf can be affected by the high frequency switching of some chargers. I bought another usb charger, different make, and no further problems.

 

[oilybilge]

Do you have an emergency antenna you can plug directly into the VHF? It's a great way to eliminate problems in the connectors and cabling, (and it's a good thing to have anyway.)

 

[steveeasy]

I’ve got another antenna on the stearn on a pole for AIS. Tried that and no different. I have to say I’ve a few 12 v charging sockets though which I’d not considered at all to possibly be a problem.
Steveeasy

 

[Plum]

I’ve got another antenna on the stearn on a pole for AIS. Tried that and no different. I have to say I’ve a few 12 v charging sockets though which I’d not considered at all to possibly be a problem.
Steveeasy

It is very unlikely to be an aerial problem as you have said you are transmitting and the Coastguard reported hearing you when you phoned them

 

[KevinV]

USB sockets are worth ruling out - I have one in the car that wipes out almost all FM stations, despite being over 2m from the aerial - it must be affecting something in the radio itself

 

[wonkywinch]

USB sockets are worth ruling out - I have one in the car that wipes out almost all FM stations, despite being over 2m from the aerial - it must be affecting something in the radio itself

It's called RFI, radio frequency interference. Cheap switched mode power supplies, USB adaptors etc are major cuplrits. Remember the old days when car ignition used to cause whining on the radio or flickering on the TV when someone drove past the house?

 

[Plum]

I had the same problem with my SH GX1700 vhf, would transmit but not receive, and after talking to a very helpful person at SH and some trials found the cause. It was a 12v usb charger plugged in to a cigarette lighter socket. Spoke to the SH man again and he confirmed that a certain component in the vhf can be affected by the high frequency switching of some chargers. I bought another usb charger, different make, and no further problems.

Further to the above, this is what the man from Standard Horizon said ".......... USB adaptor is probably using a small switch mode power supply to create the 5v. This is causing a lot of RF noise which in turn is affecting the receive ceramic filters within your radio........."

 

[wonkywinch]

it must be affecting something in the radio itself

causing a lot of RF noise which in turn is affecting the receive ceramic filters within your radio........."

It's more fundamental than this. The rogue transmission from the badly designed power supply simply swamps the RF input of the radio causing internal AGC (automatic gain control) to turn down the noise, in turn reducing the wanted signals too.

A few microwatts 5 metres away can overcome 20 watt transmissions 10 miles away.

If your antenna is at the top of the mast, ie far from the source of interference, then the situation can be improved by putting RF filters on the radio power lead (ferrite ring) and ensuring the transceiver is adequately grounded/screened. Rogue signals can then only enter the set via the antenna and/or power supply.

Try opening the squelch so you can hear the white noise then turn things on and off around the boat and see what effect they have.

 

[steveeasy]

Ok. I’ve I’ve 7 12v usb outlets within a hands reach of the radio. As well as that I managed to not refit the ferrite rings/filters to the radio.
I use these to charge 3 vapes, 2 IPads and my and others phones.
Can Filters be added to these 12 v sockets ?.
Steveeasy

 

[Plum]

Ok. I’ve I’ve 7 12v usb outlets within a hands reach of the radio. As well as that I managed to not refit the ferrite rings/filters to the radio.
I use these to charge 3 vapes, 2 IPads and my and others phones.
Can Filters be added to these 12 v sockets ?.
Steveeasy

They do not all cause the problem. I had 5 and only one was causing the problem and the new one I bought did not cause the problem.

 

[wonkywinch]

Ok. I’ve I’ve 7 12v usb outlets within a hands reach of the radio. As well as that I managed to not refit the ferrite rings/filters to the radio.
I use these to charge 3 vapes, 2 IPads and my and others phones.
Can Filters be added to these 12 v sockets ?

That won't stop them radiating crap, might stop it being put back on the 12v line though.

 

[steveeasy]

It's more fundamental than this. The rogue transmission from the badly designed power supply simply swamps the RF input of the radio causing internal AGC (automatic gain control) to turn down the noise, in turn reducing the wanted signals too.

A few microwatts 5 metres away can overcome 20 watt transmissions 10 miles away.

If your antenna is at the top of the mast, ie far from the source of interference, then the situation can be improved by putting RF filters on the radio power lead (ferrite ring) and ensuring the transceiver is adequately grounded/screened. Rogue signals can then only enter the set via the antenna and/or power supply.

Try opening the squelch so you can hear the white noise then turn things on and off around the boat and see what effect they have.

ensuring the transceiver is adequately grounded/screened. Rogue signals can then only enter the set via the antenna and/or power supply.

In practical terms grounded/screened?. Can the interference affect AIS reception too.
Would ferrite rings improve reception on AIS?

Steveeasy

 

[st599]

ensuring the transceiver is adequately grounded/screened. Rogue signals can then only enter the set via the antenna and/or power supply.

In practical terms grounded/screened?. Can the interference affect AIS reception too.
Would ferrite rings improve reception on AIS?

Steveeasy

Some transceivers have the option to attach a grounding strap to say the engine - not sure how common this is on VHF (and isn't something you can add later as altering the radio would remove the type approval)

Interference will affect all reception - although it's less of an issue on some modes which use a priori decoding (they know the timing of the signal and what the signal should look like - so it's easier to decode)

Ferrite rings on the power supply may help, if the interference is coming down the power cable. It won't help if it's entering via the antenna or via a lossy connector somewhere.