VHF range and output

[Pargo Man]

Gentlemen Anglers,

greets first. Back in Angola we all suffer from acute no-infrastructur-itis. Safety at sea therefore depends on your precautions and equipment.

Past weekend we had huge swell and chaotic chop... and so our VHF f!.?ked up. 5 times I managed to get it back to work, but some short circuit switches the VHF off as soon as I press the mic button.

Here's my request for advice (... also, if a link or thread already exists for me to do the reading..):

1. Have all VHF their output limited to 25 watt, or is there a product in the market with a bit more umpf? Yesterday we went to 42nm and after 30nm could'nt hear the NAUTICO Clube bases station any more...

2. Is there difference in the listening sensitivity and how much sensitivity is good?

3. Overall, what is a sturdy and safe product in the 200 to 350 USD range?

Bear in mind I don't actually make use of the interface options some of these fancy VHFs might have.

 

[Seeker1]

There are two things you can do to increase the range of your 25 watt VHF.

Mount your antenna as high as possible on the vessel, you can get antenna extensions which screws into your antenna and will raise the hight by up to 8ft.

Fit a antenna with the highest db gain you can get, a gain increase of 3db means a doubling of signal strength, 6db is increased 4x, and 9db is increased 8x, so try and source a 9db gain antenna.

 

[Fanie]

Hi Pargo,

Nice picture - just looking at it makes me land sick (sick of sitting on land here ;-)

The problem with VHF is it is funtional only line of sight. Iow, if you can see it you can talk to it. To increase your range a bit you will have to mount the arial higher. More watts will probably not get you better range, the 45m tower should :-D

The input sensitivity of a radio is measured in dB (decibells). The signal halves every 3dB's so if a radio is specified a signal input sensitivity of -45dB vs a -15dB radio then the -45dB has better reception because it can receive a weaker signal.

If you want better range you will have to look at a HF radio which will work beyond line of sight - depending on conditions. If conditions are good you can talk all over the world, and here watts rule, but is limited by legal allowance - unless you're a japanes trawler then 1500W plus is nothing (you just fry everyone else's radio's that gets close to you) and no laws apply to you either ;-)

If conditions are poor, usually when you need it the most ;-) you talk to yourself :-D HF, because it is a lower frequency usually requires a larger aerial, although there are some nice tricks to get past the size ($$$).

The absence of sun spots on the earth's atmosphere is improving currently, so it seems that conditions are getting better for the next period, and ranges are getting better with it.

The best way to have coms is to take the wife with :-D, second to that is probably the sat phone, then HF, then VHF, the walki talki, then the loud hailer, then shouting, and so on :-D

Mount the aerial higher or get an HF radio.

Hope this helps.

 

[Fanie]

He he... if the earth was flat it would have solved one problem here :-D

 

[Pargo Man]

Seeker and Fanie and All, big help so far. We'll get us some swift basic radio to replace the iffy one for now... and then move the antena up from 2,5m at present with sturdy "Djamila2" to the tuna tower of the next boat...

 

[Fanie]

Hi Pargo,

I would really consider the HF radio... It's got RANGE. VHF is good for local.

 

Sorry for edit - if you look at the earth's curvature you can actually calculate how much more range the aditional height will give you...

 

[Pargo Man]

2m height gives 12nm... rule of thumb.

Trouble is if we went up with the "Djamila2" antena, the shear forces in the wave would ripp it out of the hull unless we had a proper rollbar or sth...

 

[Fanie]

Aye Pargo, see, size does matter :-D