VHF Transmissions

[tgalea]

Hi,

I am encountering a strange problem with my VHF to this tune. I recieve transmissions from boats 30nm away from me but then it seems that although transmitting in full wattage only boats very close to me are recieving my transmission.

So it's ok in recieving but very poor in transmission. The vhf unit is a brand new one and tested on a fixed base antennae work correctly. Does this mean it's my boat's antennae ? But then if it is, why is it that it recieves ok but fails to transmit ?

Thanks

Tyrone.

 

[VMALLOWS]

It's almost certainly your antenna. When you're receiving, resistance and SWR (a bit technical for here) are not very important. When transmitting they are!. Try to borrow an antenna, and plug directly into the set: even at ground-level it should work fine. If not, you do have a a problem on the transmitter side.

 

[graham]

Check the coax connections are sound. Also make sure you are transmitting on full power (usually)25watts.On most sets you can select a low power setting.

If no joy see if you can try your set on someone elses boat using their ariel.If it works for them and not for you then you know the set is at fault.

You should get approximately 10 to 20 miles range at sea depending on the weather and how high your ariel is.You will allways recieve over longer distance than you can send.

 

[VMALLOWS]

Surely, if the set works on the other boat, it must be fine....not the other way!

 

[Chris_Stannard]

The problem you describe is almost certainly antenna related and to use a technical term indicates a high Voltage Standing Wave Ratio (VSWR). To check this you can do one of two things:

1. hire a technician with a VSWR meter who will test your antenna and tell you that it is not working properly.

2. Buy an emergency antenna and plug it into the back of the set. If the transmission is okay, as it almost certainly will be you know where the problem is. If it doesn't work properly take the set back for test to the supplier. However as you say it worked correctly on a fixed base antenna it does sound as if the set is okay.

I would recommend 2 since you should carry an emergency antenna as part of your standard safety spares package and it will be cheaper than 1.

If you establish that the antenna is at fault this can be due to one of thwo things.

If the boat is more than about 10 years old the insulation of the co-axial antenna feeder running up the mast may have absorbed water and be the cause of the problem. If you have your mast out at about 10 years it is a good idea to change the feeder for this reason. This is usually a slow degradation in performance.

the more likely cause of antenna problems is the plugs. There are usually three in the line, one on the back of the set, one at the base of the mast, and one at the massthead. I hate to say it but the oine at the masthead is the most likely to be at fault since it is up there in the weather where you cannot see it. I suggest you start at the bottom of the mast, and replace the connector. You can buy good BNC connectors that do not need soldering. When you take the old connector off if it is green and full of water or gunge that will be part of the problem. Try the set again to see if this makes a difference.

If it does not make a difference its hey ho to the top of the mast go and see what the connector is like up there. If you still cannot make a difference, you might at this stage try the technician with the VSWR meter.

If you do not want to replace the antenna until the end of the season buy a new antenna and fit it on the pushpit, do not cut the cable but leave it ready to fit when you next have the chance. It will make a bit of difference to the range you get but you should get acceptable performance.

Good luck


Chris Stannard

 

[Miker]

Re: My problem as well

I, too, have had the set tested which was OK, and was advised that it is most likely the connection at the mast head. So next week it is someone, most likely me, up the mast.

 

[VMALLOWS]

Re: My problem as well

Enjoy the trip up the mast.........think I'll have to do it soon......... windvane pointing in funny direction.. Trouble is wife insists I'm getting heavier!

 

[kgi]

I had a similar problem after a fairly close lightning strike, i could not understand why i could hear other vessels but i could not reply to them, it turned out my radio had been lightly "fryed"!!

 

[jimi]

I had the same problem .. it was the masthead connection!

 

[jtwebb]

Re: My problem as well

I am lucky (or my wife is) as I now have a Dehler 36 with an electric winch. I have heard of some using the anchor winch. I actually carry a power/SWR meter on board and it has been used many times to satisfy me and on other boats when they mention they have problems. When I have had such problems it has generally been at the base of the mast. One can get aerials with sealed cables but they then have to be fed from the top and are rare now I think.

J Webb

 

[tgalea]

Well yes pretty much that is that situation she is more that 10 years old has three connections.. been outside for the last 10 years.. etc .etc..

oh dear! so it looks like i'm up to the top of the mast !

Stupid question if i may. How do you climb to the top of the mast ? My boat is not that big.. can she take a persons weight hung in some way to the mast ?

Thanks

Tyrone.

 

[brianrunyard]

If set works ok with another antenna, the output stage is obviously ok. The most likely problem is a bad connection in the antenna cable are the plugs fitted properly and soldered.
A VHF will receive with a bad antenna but won't transmit. You could stick your finger in the antenna socket and receive ok, but to transmit the antenna has present a 50 ohm impedence to the transmitter to load it properly, and be properly tuned to the frequency band or the SWR (standing wave ratio) will be high, which means that a large proportion of the power will not be radiated, but will be reflected back down the cable and cook the output stage.

Regards,
Brian

Brian
http://homepage.ntlworld.com/brunyard

 

[Miker]

Re: Getting up the mast

I'm hoping that my mast is strong enough. It should be given that the weight on it is straight down. I shall choose a still day. I've got a long rope and some blocks to reduce the winching load, plus I hope to talk my crew into going up!
Best of luck with your climb.

 

[jimi]

Re: Getting up the mast

When I go up the pole I prefer to climb it myself rather than being winched. What I do is tie a halyard or the topping lift off and climb it using two loops of rope,one as a foot stirrup & the other attached to a hrness.I gain height by sliding rolling hitches up stepping in, sliding other up and so on. I use another halyard as a safety rope. I find it gives me more control.

 

[ParaHandy]

Re: Getting up the mast

Could use ascenders (mountain climbing gear)? Does same thing but without any rope twiddling hassle. I've been using mine for 2 years now (cost £85).


<P ID="edit"><FONT SIZE=-1>Edited by ParaHandy on Thu May 9 16:22:48 2002 (server time).</FONT></P>

 

[DIOGENES]

I had the same problem. It turned out to be a poor connection in the power supply causing a low voltage. Worth checking when transmiting.

 

[PuffTheMagicDragon]

Re: Climbing up the mast

Tyrone, since you are in the Gozo Marina I suggest that you do not try to go up the mast unless you are certain that the Gozo Channel Ferries are not operational! I would suggest that it could be far easier to lower your mast (tabernacle isn't it?) and then erect it again.

Wally

 

[tome]

I had the same problem, climbed the mast and all looked fine that end. Turned out to be the connector at the base of the mast (hidden under head lining) so suggest you check that first before going abseiling

 

[tgalea]

Re: Climbing up the mast

I know man!

That's actually why i'm hoping i can be lucky and do something else instead.. i'm not the type to climb up masts unfortunately.

I guess this will have to wait until next winter when she is on the hard and possibly invent something with a ladder etc.

How are you getting along ? All well i hope.

cheers

Tyrone.

 

[rogerm]

Re: My problem as well

A tip to try from the amateur radio world. Get a VHF socket (or plug) and a 12v 21W winker bulb from a car. Solder the bulb across the two socket (plug) connections. Connect it using a short lead to the back of the radio and key transmit. The bulb should light fairly brightly as long as the radio is OK and the power to it is ok. Don't keep the radio keyed for more than 10-20 seconds at a time as the bulb is not a proper match (ie 50R VSR). If it is ok there move the bulb to the mast base connection and try again. If OK there then I have to tell you that it is a masthead job. However if you don't mind buying a spare aerial (and you should have one in anycase) attach it to the spinaker halyard and haul that up the mast as a stand in. Of course it will flap around some (which is not good long term) and you need to be sure that the whip part of the aerial is not touching mast metal (otherwise it won't work much better than your original aerial) but you should be able to 'get out.
Roger