Difficulties with reception/transmission on VHF

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portvasgo

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Sailing the north coast of Scotland as my home waters, there is little VHF traffic, I therefore use it rarely. However towards the end of last summer, I hailed one of the local fishing boats, he heard me clearly, however I could not pick up his reply. I further checked this by calling Aberdeen Coastguard, and it seemed they received my signal as I heard an attempted reply - only static. I therefore assumed there was something wrong on receiving signals. However, I did not know whether it was the VHF unit or the aerial.
During the winter, I put my VHF unit onto the aerial in another boat, and the result has me totally bamboozled. With the use of a hand held VHF and putting my VHF on the other boats aerial it seemed the opposite problem was happening, that is - the VHF was receiving ok but not transmitting!
At the moment my boat is demasted and it is therefore really difficult to connect my VHF to my own aerial, so I'm left still not knowing what's going on, anyway if I use my own aerial I'm back to not knowing which is at fault - aerial or unit.
Does anyone have any idea what might be going on, I am starting to doubt whether I have got mixed up with what was happening in the summer.
My main question is. If it is the aerial that is at fault would both transmission and receiving be affected. I.e. if it was the aerial would everything be dead or static? Or should I just go and get a new VHF unit, I should probably get a new DSC unit, as my current one is quite old. But with my luck I’ll connect everything up when the mast is put back up, and it still won’t work!
Any advice would be greatly appreciated. Keep it simple though – as you can no doubt tell, I’m a novice at this!
Thanks.
 
Cuddy, as you say, a bit of a dilemma! What I would do is attack the cheap options first. You said that the radio is quite old so I assume the aerial wiring is also old. Whilst the mast is down, remove the old aerial cable and replace with new and, at the same time, replace the aerial connectors. That lot should not be expensive. When the mast is erected again, try the radio. At this stage you will know that the aerial side of things is not the problem. If the problems still exist, consider replacing the radio. Perhaps borrow a friends radio and try on your aerial set-up? Should the transmitting problem still persist, I would check all the radio power connections.

Hope this is of some use, SP
 
Puzzling as you say.
You might expect to get reception of a strong local signal even with a defective aerial but no be able to transmit. In fact just a short piece of wire plugged into the aerial socket enabled me to receive the old coast radio station whose transmitter was not far away from me at home.

With a hand held set I would try testing the receiver with just a make shift aerial and the H/H local to it. You will have to use a suitable single frequency channel, ie an inter-ship one to be sure that the receive and transmit frequencies are right.

Taking your radio to another boat and trying it on a known good aerial is the best way of checking your set though, as you have in fact done, but I note you then used a hand held to check it. Did you use a suitable channel (inter-ship).

Personally i would feel inclined to do a radio check with the Coastguard if possible but if you must use a H/H it would be sensible to be certain that it is working properly.

Final thought check the power supply to your set if you find it is recieving but not tranmitting as it takes much more current to transmit.
 
[ QUOTE ]
Are both radios set to international settings

[/ QUOTE ] I dont think that is an issue if you use a single frequency intership channel, which is why I suggested it.
In the USA some channels that are two frequency channels elsewhere are single frequency, but they are, of course, not intership channels.
However it is quite sensble to check as it is not unknown for sets to be inadvertently switched to the USA channels where the facilty exists. It could affect ship to shore communication because the ship would be listening on the wrong frequency.
AFAIK the channels affected are 07, 18, 19, 21, 22, 23, 65, 66, 78, 79, 80, 83 & 88
 
If the VHF will transmit but not receive from the C/G then it is highly unlikely to be the aerial. Typically a problem with the aerial would show as being able to receive, but not transmit.

Beware of drawing conclusions as a result of testing with a handheld in close proximity to the VHF set. The power (relative to the distance) will be so high that you won't learn much useful from it.

It seems that you do not have enough information to make a realistic diagnosis without connecting the VHF to the aerial and doing more tests. From what you say it sounds more like a problem in the receiving circuit than the aerial.

A pragmatic solution might be to replace the VHF aerial anyway while the mast is off the boat - on the grounds that a new aerial is pretty cheap and it would be much harder to do once the mast is up again.

The fact that you
 
If it transmits, I would say your aerial is fine. If the aerial is disconnected or shorted when you transmit you will destroy the output stage of your transmitter (don't ask how I know this!) /forums/images/graemlins/mad.gif

It may seem a bit puerile, but how do you adjust for squelch? The normal way is to turn down the squelch control til you get the horrible noise & then slowly turn up until noise disappears. As I understand it this gives you maximum signal to noise reception. I suspect that if the squelch knob is turned all the way reception may be just too quiet.

Otherwise there may be a fault on the reception side of your set. I tend to leave mine on 16/64 dual watch so I get other people's forecasts without having to irritate CG by asking for yet another one!
 
A radio workshop should be pretty easily able to check out the receiver and transmitter performance. However costs for service can be such that a new DSC set would be the way to go. DSC may be valuable in an area with not much radio activity. A radio should be used often to ensure it is working and to keep your own hand in with confidence.

The other option which has long term value is to make or buy a standby antenna that can be mounted on the stern rail. That can be really good in a dismasting!!!

Radio must be one of the greatest aids to improve safety of modern sailing it would be a pity not to use it.

Around here by law you must have a working ship radio if you venture more than 3NM from shore. olewill
 
[ QUOTE ]

I tend to leave mine on 16/64 dual watch so I get other people's forecasts without having to irritate CG by asking for yet another one!


[/ QUOTE ]

I feel sure this is a typo and SeaRush meant 16/67
(in case by remote chance someone is misled, can't call the coasties, drowns, causes the world to end, sues everyone: you know the sort of thing...)
 
We had a similar problem in a friend's boat last year - and suspected the aerial at the mast head. Eventually, we bought an emergency aerial (about £35 from eg Compass) to test out the radio separately from the mast aerial. This plugged into the back of the radio, and we taped the aerial to the backstay. Found that it all worked well, receiving and transmitting. So at least we knew that the fault was in the main aerial or the wire up the mast (which has several joints).

Not a bad piece of kit to have on board anyway, as it could be used in case of emergency, or simply have doubt about the main aerial working properly.

The other problem we found last year was with a hand held - which could be (inadvertantly) switched to the US channels rather than the international set. One feature of the difference is that Channel 80 is duplex here, but simplex in the US. So if you call the marina in the UK using US Channel 80, they can hear you, but you cannot hear the reply! Once you know, it was easy to switch back - but it did cause confusion that day. On that particular model (Icom), the US channel is shown as 80A, so now we know the significance of the "A".
 
Thanks for all the advice.
Still not sure what to do. Although I feel the consensus is that it is perhaps likely to be the VHF unit, it seems that it might be prudent, saying as the mast is down, to replace the aerial as a first step. Now this is where I become a little unsure (showing my novice status). If I am to replace the aerial set up, do I just have to replace the cable, or do I need to replace the aerial as well (it has a Windex unit that I will have to hope will fit onto the new aerial) along with the deck gland connector and the cabling that runs behind the coach roof lining? Looking at my local chandler’s brochure, I can get a V-Tronix antenna with 20m cable for £49, a new deck gland plug and socket for £25, about £75 all in although I may need more cabling to run from the deck gland to the vhf. Mind, in the same brochure, an ICOM 411DSC/VHF unit is only £130!

Thanks again, and any other thoughts are more than welcome.
 
If you guys are ever in La Coruna, check me out.. I have a full diagnostic rf workshop on board Ruddles.

I also have state of the art antenna analysers here..

Sorry to be so far away.. its only 20 euros for a full system wide check including antennas and feed, transmit and receive etc.. with written report..

Dont get too carried away with the 'if it tx's it is not the antenna'

Sometimes the antenna beocmes a 6" strand of old coax lol.. it WILL tx ok close up... but rx is crappo... Most modern sets can simply wind back thepower to protect itself.. the days of the popped tx PA is history to a great extent.
Get an SWR meter and check the reading, below 3 is fine.. best way to tell quickly.. Also, check the current consumption on rx and tx, tx should be around 3 to 5 amps....

Hope you get it sorted, sounds like an antenna and coax change is called for....
 
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and any other thoughts

[/ QUOTE ]
Thoughts then, not in any particular order of importance although I would try to establish what the fault is rather than indiscriminately replacing stuff. Maybe some have already been covered

It is difficult to check the aerial and cabling in the mast so replacing it before stepping the mast makes sense if there are any doubts about it.

The wind vane will not fit on any old aerial so you will have to get the correct one to take the vane you have. It may not be available without a new vane.

The aerial could be defective or the cable could be defective, damaged by water ingress perhaps.

The wiring inside the boat is not likely to be defective but it can be checked for continuity of both inner and outer conductors and for shorts between the conductors with a multimeter. If for some obscure reason a fault exits that is not detected it can be changed at a later date.

Check deck plugs or junction boxes carefully for defects and good connections.

The cable in the mast can only be checked (in the same way as the cable in the boat) if it is connected to the aerial with a plug and socket, some are but many are not. you cannot check the aerial with multimeter, or the cable with the aerial connected.

Follow the instructions for fitting plugs etc on to coax cable carefully.
 
The cable is usually permanently connected to the aerial, so replacing the aerial implies replacing the cable as well. In fact any problem is much more likely to be in the cable than in the antenna itself.

IMHO deck connectors are the work of the devil - particularly for VHF. My preference is to use glands and to make the connection inside the cabin where it is not so prone to water getting in.

If you have a deck plug then it is almost certainly the weakest point in your set up. Either the connections themselves get oxidized, or they let water in that corrodes the junction with the cable, or the cable itself.
 
[ QUOTE ]
If you have a deck plug then it is almost certainly the weakest point in your set up

[/ QUOTE ] Mine has given no trouble since it was fitted in 1985. Although I suppose it leads a relatively sheltered life. I usually give the contacts a very light smear of silicone grease. When laid up during the winter the socket is always capped with the plastic cap that was supplied with it and the corresponding plastic plug is always screwed into the plug, which spends the winter hanging in free air tucked under the cover. The boot is still in good condition and a smear of silicone grease on the outside of the cable helps it to slide into place easily and keeps it waterproof. No added sticky tape or self amalgamating tape.
 
I suspect you don't actually know that the coastguard heard the call clearly. If the reply was from him, it could have been "station calling blabla coastguard, your signal is keech, please repeat" but because nothing much is happening up the mast, you misinterpreted. As others have said, check for blackened copper on the cable and replace if dubious. If you have an ammeter fitted to the boat ( or can measure temporarily) the VHF should take about 5 amps from a 12volt source at full (25watt) power. If it doesn't, it's not working right. ( it will reduce power automatically if it 'sees' mismatch reflections from a poor aerial)
 
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