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Old 13 January 2010, 15:08   #11
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Just a quickie
For info only
VHF works by line of sight

So if boat 1 has a 10ft high spike
And boat 2 has the same

Theoreticlly each will 'see' each other for 4 miles
Therefore they can communicate if they are 8 miles apart.

I,m sure you all wished to know that

OK
I,ll feck off and go and watch the footy Then
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Old 13 January 2010, 15:22   #12
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So if boat 1 has a 10ft high spike
is that measured from the base of the antanae or the top? makes a big difference on a small rib/sib especially with no a-frame
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Old 13 January 2010, 16:39   #13
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The main issue I could see with transom height is you will make a very good absorber for the outgoing signal, esp. if you are on 1W ......
And I haven't even got a profile picture... ;D
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Old 13 January 2010, 16:44   #14
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I think I will go with what you describe Malthouse, but there is a small chance I will build some kind of DIY A frame.
Does your shop stock the things you mention?

Thanks everyone for your help,
Geoff
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Old 13 January 2010, 17:03   #15
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This probably won't be relevant to you Geoff but one thing that we find is that a large proportion of ariels are supplied with a five meter cable and we would advise avoiding any joins or extension cables where possible so may be worth checking that the aerial that you are looking at will have a long enough cable with it
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Old 14 January 2010, 02:11   #16
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Quote:
Originally Posted by Polwart View Post
is that measured from the base of the antanae or the top? makes a big difference on a small rib/sib especially with no a-frame
The theory is, 10ft above sea level.

So in realty it is just a fairly accurate guidline.

Yachts for instance.
Will enjoy better ship to ship communication with their 'spikes' mounted on top of a tall mast.

30ft (above sea level)for those chaps would give them about 8 miles each.
Therefore a 16 mile 'range'

Then again weather conditions, the sea bobbing us up and down etc will affect reception etc.

Basically, the higher the better really though.

Obviously HM Coastgaurd has antennas dotted about the place.
Which is why sometimes you may hear the CG transmitting when you are 20 miles from Him
But you wont hear the vessel responding.

For instance
I like to stick me radio on Ch 84 Holyheads CG's Ch for 'routine traffic' normally and stick the 'dual watch' facility on.

So 16, cos everything starts there, or should!
Plus on 84 I can hear the CG and sometimes the vessel responding.

Just kinda makes me feel safe, to know who is about and whats going on.
Plus I,m a nosey git
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Old 14 January 2010, 03:29   #17
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Quote:
Originally Posted by kawasaki View Post
The theory is, 10ft above sea level.

So in realty it is just a fairly accurate guidline.

Yachts for instance.
Will enjoy better ship to ship communication with their 'spikes' mounted on top of a tall mast.

30ft (above sea level)for those chaps would give them about 8 miles each.
Therefore a 16 mile 'range'

Then again weather conditions, the sea bobbing us up and down etc will affect reception etc.

Basically, the higher the better really though.

Obviously HM Coastgaurd has antennas dotted about the place.
Which is why sometimes you may hear the CG transmitting when you are 20 miles from Him
But you wont hear the vessel responding.

For instance
I like to stick me radio on Ch 84 Holyheads CG's Ch for 'routine traffic' normally and stick the 'dual watch' facility on.

So 16, cos everything starts there, or should!
Plus on 84 I can hear the CG and sometimes the vessel responding.

Just kinda makes me feel safe, to know who is about and whats going on.
Plus I,m a nosey git
I know that - I am familiar with the numbers which have all been posted here in the past. But you didn't actually answer the question - can I expect to be able to talk to an identically rigged boat from at 8 miles if I have a a 10ft long aerial mounted at the top of the transom or only if it is in fact 10 ft above the gunwale?
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Old 14 January 2010, 04:07   #18
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Quote:
Originally Posted by kawasaki View Post
The theory is, 10ft above sea level.

So in realty it is just a fairly accurate guidline.


I don't think it would make a great deal of diffence if it was mounted on the transom or the gunwhale.

Higher the better obviously.

Just trying to point out the type of range we can expect rib to rib.

VHF as we know is 'line of sight' .

But as others have posted.
There are other things to consider.

Tother thing
Like land in the way
Sometimes I have locked into Port Dinorwic marina.
The Dockmaster has an ariel on His office roof.
Dunno
Could be 40ft up.
Until I clear a headland approaching from the North its about a mile away until He hears me
Tother way I can raise Him from about 3 miles away
The spike on me little mobo is about 10ft above sea level.
Figures I gave are probaly 'in the best possible scenario'

Just as a guidline.
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Old 14 January 2010, 04:12   #19
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I don't think it would make a great deal of diffence if it was mounted on the transom or the gunwhale.

Higher the better obviously.
I think your misunderstanding me. I'll post a piccy later.
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Old 14 January 2010, 04:35   #20
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Quote:
Originally Posted by Polwart View Post
is that measured from the base of the antanae or the top? makes a big difference on a small rib/sib especially with no a-frame
I tend to measure effective heights of antennae from two thirds up the active length.

There is a proper rule, I will see if I can dig it out.
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