[MarieK]

I was out at a wreck last week and tried to call up a mate who was 10 miles away. I could hear him ok chatting to other boats but he could not hear me.

The radio works fine when we are close. My question is, where do I start trying to diagnose the issue. If I can hear him does that rule out the antenna?

If I was going to buy a new antenna to increase range is there an optimum size I should go for?

Also on the off occasion I get a low battery message on the vhf. Now the battery is in good nick and I have been over the wiring to the radio, it is all fine and the correct gauge.

Its an Icom m401

Ryan

 

[Guest]

Are you definitely on High Power? Obvious question I know but best to start with the obvious. I would also check that you are getting full power to the radio, maybe you have a bad or corroded connection somewhere in the power supply causing a drop in current occasionally and therefore giving the low power message.
As for getting a new aerial, the longer the better as VHF works on line of sight. I use a 3mtr Antenna fitted as high as possible on the boat.
My opinion here is based on various problems I get from time to time with our taxi radios which are also VHF.

 

[MarieK]

Yes on high power - I have checked connections for corrosion but I guess its the obvious one. How often do you replace the antenna on the boat?

 

[MikeD]

I agree with cascars comments, but equally important is the condition of your coax cable and connectors. For a transmitter aerial to work correctly you also need a groung plane which has to be metal. This could be a rail or frame of some type on your boat, or if mounted on the cabin roof, it should be a flat plate. This works as a reflector for the aerial. The coax has two cores, the inner connected to the aerial and the outer sheath connected to the ground plane.

 

[gibberfish]

If your boat is a smallish one (under 30 ft) do not get an ariel that is too long. Longer is not always better on small boats that tend to roll about more. Longer ariels will concentrate the signal into tighter band but it is more likely to miss as the boat rolls, particularly at increased range. You will get a more consistent signal (transmitting) if you stick to about 1.5 meters, unless you are sure that you will never need a radio when you are rolling about a lot (like when the engine fails).
You wont see a 3 meter ariel on an inshore lifeboat - even a 25 foot one.

 

[alankirby]

If your boat is a smallish one (under 30 ft) do not get an ariel that is too long. Longer is not always better on small boats that tend to roll about more. Longer ariels will concentrate the signal into tighter band but it is more likely to miss as the boat rolls, particularly at increased range. You will get a more consistent signal (transmitting) if you stick to about 1.5 meters, unless you are sure that you will never need a radio when you are rolling about a lot (like when the engine fails).
You wont see a 3 meter ariel on an inshore lifeboat - even a 25 foot one.

Spot on info.:clap3: The height of the antenna above sea level is far more important than the length.
If you really want to be baffled with the science of it all then have a read of this,
Scroll down to the "Line of site path" part and it will tell you about rolling boats ect.
http://continuouswave.com/whaler/reference/VHF.html

Alan

 

[R3k]

A rough rule of thumb is 1 watt of power will travel 1 mile.

Take a look on the back of the VHF at the antenna connection. It should be clean. If there is evidence of corrosion then there is probably water in the cable (fairly common).

 

[ChrisP]

Don't know if you have ever looked inside your VHF ariel but it is really basic in there. It ammounts to a length of stiff wire soldered to the centre conductor of the coax. Any water in there and you get corrosion, it will receive fine but when it comes to transmit it will break down as you are putting much more power through it.

Some ariels cannot be dismantled to check this but for £30 it is worth fitting a second ariel to the boat. I have 2 on mine and swap the PL259 connectors over monthly to make sure I have good TX/RX and a reliable spare should I need it.

In my expeirience 90+% of VHF problems are in the ariel not the set.

 

[AHoy]

If the other boat has its aerial higher above sea level then he will have significantly more range (line of sight propagation of radio signal). Is the other boat bigger with wheelhouse, radar arch and the aerial mounted up high? With an aerial mounted on the average cuddy the range would be about 3 miles to the horizon.

 

[Davy Holt]

Hiya,

is the aerial vertical ??

I was always told that because of the way it broadcasts the signal, if it's not vertical you will be able to get a good signal in one direction and a poor signal in the other direction.

 

[MarieK]

I dismantled the aerial over the weekend and it looks like water has got in alright. The main conductor was green! I thought if I could receive well then this ruled out the aerial but what you say Chris makes sense. I suspect a new one will sort out the problems.

The aerial is vertical now after I read that in another post about a year ago. Thanks.

The other boat was identical to my own so same height from the water.

Thanks guys,

Ryan.