Distortion in VHF transmission

blackbeard

blackbeard

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Transmissions from my VHF are heard as "loud, but distorted/ barely readable". However transmissions from other sets are received normally.
Does anyone have any idea what might be causing this (or am I describing a problem with too many possible causes?).
Set is a Simrad and there is a "splitter" between it and the aerial (so that the aerial can be used with a "domestic" radio (from a crashed MR2 I'm told)).
I have had various problems with the deck plug for the cable (from set to masthead whip antenna). I THOUGHT I had solved this but now I'm not so sure ... but as the problems occurred both pre and post "solution" it might be something else ... any ideas?
 
Can you borrow an aerial and cable and mount it temporarily at deck level? Would sort out immediately if it was cable/aerial problem, or set problem.
 
As Brendan suggests or take your set to a boat with a known good aerial and try it.
Chug down to Lymington on the weekend and try it on his boat!

Take Brendan's VHF off his boat and try it on your aerial too.

I'd try it without that splitter as well.

Above all else check the power supply to your set. It recieves on a few milliamps but it needs a good supply of several amps to transmit.
 
I find the word "distorted" might be the clue in this problem?

Is this distortion always present or only when turned up loud enough to hear throughout you boat?

If you turn the volume right down so it is just audible and listen very closely to the loud speaker, is the problem still apparent? You might have audio distortion due to either a duff loudspeaker or an electronic fault called third-harmonic distortion?
 
OK on that /forums/images/graemlins/confused.gif

Therefore I ask, when this "distortion transmission test" is being conducted, is the 'receiver set' used for the test in close or very close proximity to the suspect faulty set doing the transmitting?

If so, the receiving set could be suffering from 'Front End overloading'? /forums/images/graemlins/confused.gif
 
I wonder if possibly you are shouting too loud into the microphone. If you can get someone to monitor your transmission try speaking more softly. You may have a bad microphone itself. If you can swap it for a known good one that would prove it.

I doubt any problem with the antenna would cause distortion. Usually just poor range. good luck olewill
 
Some "comfort" equipment have been known to cause distortions, eg frigde, HF chargers, GPS antenna wire along VHF antenna wire.. could give it a try with only the VHF powered on, see what happens..
 
From what you say, the two obvious suspects are splitter and coax plug.


I think I am right that all splitters 'fall back' safely to a transmission path for the VHF if they lose power. So 1 simple test would be to remove power to the splitter (it would be wise to unplug the ant from the "domestic" radio) and see if that changes anything. That will tell you if it is the splitter itself as opposed to its antenna connections.

Next suspect is one of the several coax connections in the path. I hate coax deck plugs and have seen lots of problems with them. Depending on the problem I think you could get a distortion from a poor connection. So as others have said, try your emergency antenna plugged straight into the set.

Poor power connections are possible, but will I think make the set flick on and off as you transmit rather than distorting. But you could try looking at the voltage across its input plug when transmitting vs receiving.

Otherwise, the next best explanation is that the radio is, to use a technical term, knackered!
 
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