Poor VHF reception

[Guest]

Is there a test for a fixed VHF antenna? My set ( Demek Sealine) doesn't receive many transmissions picked up by others nearby and transmits weakly. I have fitted a new antenna plug. Is this likely to be the set or antenna? It is outperformed by a handheld. Antenna is atop a 10m mast.

 

[Chris_Stannard]

Yes there is a VSWR (Voltage Standing Wave Ratio) test which will show if there is a problem.
First step, if you have an emergency antenna rig it and see if you get good performance. If you do it is the antenna, which is the most likely cause. If not it could be a failing component in your set although this sounds not to be the case.

If you decide it is the antenna, then the VSWR test will tell you how bad it is, but before you do that you need to look at the connectors, which are usually the source of the problem. There will be at least three, the one to the set, the one at the base of the mast and the one at the top. Corrosion in any of these will be a major problem and the most likely to be at fault is the one at the top of the mast.
If there is corrosion replacement is the best answer. If there is still a problemand if the co-axial cable is old it may have absorbed water. the VSWR test is the only way of finding out if this is the case.

If your antenna is old, and you have established it is the problem by step one, it might be quicker and easier just to replace the whole thing. I understand that you can get connectors these days which do not need soldering, but protect them as best you can, with rubber sleeves etc.

Hope this helps

Chris Stannard

 

[Guest]

modern electronics, if they fail, tend to fail completely. so it is much more likely that your aerial is the problem. as Chris says, the way to test this is to measure the ratio of power transmitted to power bounced back (the swr) but this requires a meter to be inserted between set and aerial. you might well be able to buy a cheap meter from maplins.

the alternative is to beg borrow or steal a known good aerial to connect up and try. if you cannot do this by moving an aerial to your boat, then move your vhf to a friends boat.

before you do any of this, however, check all connections, partic of aerial.

 

[Piers]

I'm in agreement with the other two replies - the most likely problem is the aerial, or the cable to it. The SWR meter will verify this for you.

I had exactly the same problem, and it was cured by reaplcing the aerial.

Piers du Pré
MBM Cruising Club enthusiast
www.dupre.co.uk/fsPlaydeau.htm

 

[gtmoore]

I had exactly this problem and traced it to a faulty plug connection at the foot of the mast. It's the type that screws into a connection in the deck and I just gently tugged the wire and it came out. After resoldering it the radio has been fine.

 

[brianrunyard]

I don't suppose you're anywhere near Poole Harbour are you?
I've got a professional VSWR meter you could test your antenna with.


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

 

[Guest]

Thanks all for v useful advice. Brian, I am in N Wales but thank you anyway.
Andy

 

[ccscott49]

Using a SWR meter is straightforward, but what it is telling you is not, I agree with verybody here, but would tend to get a man with the meter who knows what it is saying, the readings will tell you which connector or twhat is wrong, if read correctly, saves a trip to the masthead, if the problem is not there. I know this is PBO forum, but sometimes its easier to get an expert, or a friend who is, thats cheaper!!!