Interference on Channel 16

[gandy]

Hi,

Last week when we were on a trip there seemed to be continuous interference on Channel 16, almost as if someone had the mike pressed. It started one afternoon, was still there all the next day, then not there the day after when we were around 25 miles further on.

Our main set, Icom 421, showed "Busy" whenever tuned to 16, same with our hand-held. No interference on other channels - as soon as the channel was changed it would go quiet.

We heard it on the hand-held even with the boat's main battery switched off.

Could this be something local on our boat? I find it hard to believe that Chan 16 was blocked out for over a day.

 

[bluedragon]

Not as bad as this, but I often find the same thing around the Bristol Channel. Only Ch16 and can be resolved by turning up the squelch...but then often as not it suddenly disappears. I initially thought it was interference on board, but then why just 16? I'm puzzled also.

 

[wooslehunter]

People often put handhelds in a packet or sit on them causing the PTT to be pressed. Or, a fixed mike will fall and get the PTT pressed. If it's this kind of a jammer, you'll most likely hear something. If it's something local, you can switch off everything in turn and see if goes away. With a handheld it's easy. Just throw the master switch on the boat and the handheld should go clean.

In our area it happens quite a lot. Most people don't realise that their position can be triangulated from fixed coasty DF sets. The vessels can easily be found by plenty of "official" boats that also carry DF sets. Jamming 16 is potentially very dangerous.

 

[Richard10002]

Does it go away if you increase the squelch? I dont really know what squelch is, but it seems to be sme kind of tuning thing,so it might be that 16 needs more tuning than other channels.

Someone else will come along and give us some detail on squelch, I'm sure.

 

[savageseadog]

The squelch function cuts off the audio ouput depending on the level of the received radio signal. When you set the squelch level you are effectively saying if the signal is less than a certain small level I don't want to hear it. There is always some kind of noise in the receiver circuit and the FM decoder won't start to work until a sufficient level of signal is received so to save you hearing a hiss and all sorts of garbled half heard rubbish,you are setting a level such that you will only hear readable speech.

 

[brianrunyard]

Probably someones set permanently on transmit.
I've heard it in the Poole area, sometimes for several hours.
Probably someones mike has slipped out of it's holder or something is put against it pressing the ptt switch.
Sometimes hear Solent or Portland Coastguards telling people to check their sets, daft thing is the culprit wouldn't hear them.

Squelch has nothing to do with "tuning", it sets a "Threashold", received signals with a strength below the threashold are not heard, stronger signals are.

 

[jimg]

Do you have any older Raymarine kit installed? A long shot, but I have seen this before.

 

[DipperToo]

I had similar issues with CH80. After isolating all electronics in sequence, it turned out to be a faulty Navtex receiver when set to 'National' only frequency. Set repaired and an oscillator was changed. No problems since.

 

[gandy]

[ QUOTE ]
Do you have any older Raymarine kit installed? A long shot, but I have seen this before.

[/ QUOTE ]Ah ... we have ST30 log/sounder, and an old AH1000 tiller pilot.

But the interference persisted when the boat's main battery switch was turned off. Of course that we just a quick test using the hand-held, so its possible I didn't test rigorously. If it happens again I'll try just switching the sounder off.

Turning the squelch right up made the interference cut in and out at random - actually more irritating than continuous noise.

 

[jimg]

If the kit has no power then it should not interfere!

 

[gandy]

[ QUOTE ]
If the kit has no power then it should not interfere!

[/ QUOTE ] Yes, what I mean was that we tried a few settings of squelch, different channels, engine on and off, and using the hand-held while the fixed set was off. During all of those the echo sounder would have been on. I wouldn't swear that the test with the hand-held and the main battery off was that rigorous. Possibly I didn't confirm squelch was set right or something.