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Old 31 December 2013, 09:41   #21
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Hi Simon

Thanks for that - a crazy and sad situation, so good to say you are taking responsiblity yourself.

Here's hoping you'll never need it.

All teh very best for 2014

Steve
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Old 03 January 2014, 12:32   #22
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In that case I'd be looking to buy the 25W fixed units to install on the boats rather than handhelds (5 or 6 Watts) for greater coverage, esp as the latter can be cheaper, plus less likely to go flat due to lack of re-charge by colleagues.

And then have a 25W fixed unit on your boat, plus a handheld clipped to you.

DSC would be a very good idea too so that they will alert even if the audio is turned down by the other boats.
I agree with all these arguments.
But the range of the radio horizont is defined by the high of the antenna.
Propagation of VHF waves fllow the line of sight.
So the 25 Watt output compared to 1 or 5 Watt of handheld will only give a minor increased coverage.
Wilhelm
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Old 03 January 2014, 12:52   #23
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I agree with all these arguments.
But the range of the radio horizont is defined by the high of the antenna.
Propagation of VHF waves fllow the line of sight.
So the 25 Watt output compared to 1 or 5 Watt of handheld will only give a minor increased coverage.
Wilhelm
VHF propagation is governed by things other than antenna height. A 25w radio will have a 6db transmit advantage over a 5w handheld. When coupled with a more efficient antenna than the highly compromised helicals that most handhelds use, a fixed VHf will be far more efficient on both RX and TX.
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Old 04 January 2014, 06:25   #24
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So the 25 Watt output compared to 1 or 5 Watt of handheld will only give a minor increased coverage.
Wilhelm
Hello Wilhelm - thanks for contributing to the thread, but that assertion is not correct, as other people with amateur radio licences (where much more radio theory is taught) as well as marine VHF licences are commenting. While we can talk about db gain, in practical terms the difference between 5 and 25 is very significant. Yes the antenna is a significant element, but power is also.

While VHF is often termed "line of sight" for simplicity compared to HF units, that's not completely true and VHF does, in effect, travel around corners and over cliffs to a far greater degree than, eg, mobile phones. Indeed it is in those marginal situations of getting around a hill or cliff where 25 Watts of power is especially helpful compared to a 5 Watt handheld using the same antenna.

Cheers

Steve (GM6HBZ)
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Old 04 January 2014, 06:32   #25
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...and Wilhelm appears to be teaching the SRC, if his sig is anything to go by.
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Old 04 January 2014, 06:47   #26
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...and Wilhelm appears to be teaching the SRC, if his sig is anything to go by.
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Old 05 January 2014, 16:49   #27
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In that case I'd be looking to buy the 25W fixed units to install on the boats rather than handhelds (5 or 6 Watts) for greater coverage,
I agree with Copinsay to us a fixed radio with 25 Watt.
But it is wrong to expect a radio horizont higher than
H (in nm) = 2,5 x Sqare out antenna high in meter.
Yes I am teaching SRC,
and I am a HAM (AC1WA/DC1WA)
I sailed from Tenerife to Madeira and was astonished
to get half the way near Islas Salvages
a call from Tenerife Traffic over a distance of 135 nm.
The reason is the antenna in Tenerife is located
at apr. 2.500 meter high (with 25 Watt).
From a sailing boat with 16 meter mast high you get 10 nm radio horizont.

You might get a reflection from a cliff 100 meter high up to 25 nm.
And in inversion weather condition propagation from Norway to Germany.
So it is good to have 25 watt power,
but that will give not significant more security.
Regards, Wilhelm
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Old 07 January 2014, 02:43   #28
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I sailed from Tenerife to Madeira and was astonished
to get half the way near Islas Salvages
a call from Tenerife Traffic over a distance of 135 nm.
The reason is the antenna in Tenerife is located
at apr. 2.500 meter high (with 25 Watt).
I got a PM and will explain the argumentation.
With a very high antenna the power of 25 Watts is still suficient to provide a comunication over 135 miles.
The quality was very noisy , so I estimate that distance as a maximum.
The rangers of the Islas Salvages national park told me,
that they can listen regulary to transmitter based on Tenerife,
even handy comunication was possible some years before.
So the coverage of 135 miles is not a effect of a propagation abnormity.
When the line of sight is less, eg only 5 miles, than there is sufficient power for a good comunication.
In the area of the line of sight there is a power loss of 6 dB when the distance is doubled.
The power loss outside of the line of sight, yust over the radio horizon,
must be asumed to be quite high.
Only a small fraction of the VHF energy is bend.
Greetings Wilhelm
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