VHF Range

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tarik

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Evening all,

I know that the visible horizon - give or take an inch is about three miles, could somebody please give me an idea as to the range of the VHF radio, assuming that the aerial is at the top of the mast. I'm thinking of Ch 16 and then switching to another working channel for communication etc.

As always many thanks for all replies.


David
 
tarik said:
Evening all,

I know that the visible horizon - give or take an inch is about three miles, could somebody please give me an idea as to the range of the VHF radio, assuming that the aerial is at the top of the mast. I'm thinking of Ch 16 and then switching to another working channel for communication etc.

As always many thanks for all replies.


David
Click to expand...
Rules of thumb:
The distance to the visual horizon (in miles) is about 2x the square root of the height of eye (in metres)
The distance to the radar horizon (in miles) is about 2.2 x the square root of the height of antenna (in metres)
The distance to the VHF horizon (in miles) is about 3 x the square root of the height of antenna (in metres)

But the distance at which you will actually see.detect/receive also depends on the height of the object -- you need to work out the range of its horizon as well.

So for instance, the range at which someone on a boat with a height of eye of 4metres will see a lighthouse 49m above sea level is
(2x root 4) + (2x root49) = 4+14 = 18 miles.
Two yachts with VHF antennas 16m above sea level should be able to communicate at (3xroot16)+(3xroot16)=24 miles

But please bear in mind that although these rules of thumb generally work, they are (a) approximate and (b) take no account of unusual refraction, attenuation, luminous intensity, transmitted power, reflectivity, radar cross section, sensitivity, etc. etc.
 
timbartlett said:
Rules of thumb:
The distance to the visual horizon (in miles) is about 2x the square root of the height of eye (in metres)
The distance to the radar horizon (in miles) is about 2.2 x the square root of the height of antenna (in metres)
The distance to the VHF horizon (in miles) is about 3 x the square root of the height of antenna (in metres)

But the distance at which you will actually see.detect/receive also depends on the height of the object -- you need to work out the range of its horizon as well.

So for instance, the range at which someone on a boat with a height of eye of 4metres will see a lighthouse 49m above sea level is
(2x root 4) + (2x root49) = 4+14 = 18 miles.
Two yachts with VHF antennas 16m above sea level should be able to communicate at (3xroot16)+(3xroot16)=24 miles

But please bear in mind that although these rules of thumb generally work, they are (a) approximate and (b) take no account of unusual refraction, attenuation, luminous intensity, transmitted power, reflectivity, radar cross section, sensitivity, etc. etc.
Click to expand...

You make it look so simple!;)
 
Another simple observation is that around HW (Cherbourg) it is usually possible to hear Solent CG from Cherbourg marina. I guess this computes, more or less.

Mast ht = 17m
Boniface Down antenna = 234m
combined range = (3*root 17) + (3* root 234) = 58M
 
The range also depends on the radio and aerial being in good working order. As a rule, I have usually found that you can rely on yacht to yacht communication up to about 15 miles, though I have often had good contact with another boat at more than 20 miles, even when partly across land. On one occasion we managed over 40 miles.

Ground-based aerials sometimes carry a long way. On one occasion we heard transmissions from Jersey Radio and Yarmouth Coastguard (Norfolk) from the same position.
 
tarik said:
Evening all,

I know that the visible horizon - give or take an inch is about three miles, could somebody please give me an idea as to the range of the VHF radio, assuming that the aerial is at the top of the mast. I'm thinking of Ch 16 and then switching to another working channel for communication etc.

As always many thanks for all replies.


David
Click to expand...

The reception distances between aerials at various typical heights is part of the VHF licence course syllabus. You arent using the VHF without a licence are you? :eek::eek::eek::D
 
johnalison said:
The range also depends on the radio and aerial being in good working order. As a rule, I have usually found that you can rely on yacht to yacht communication up to about 15 miles, though I have often had good contact with another boat at more than 20 miles, even when partly across land. On one occasion we managed over 40 miles.

Ground-based aerials sometimes carry a long way. On one occasion we heard transmissions from Jersey Radio and Yarmouth Coastguard (Norfolk) from the same position.
Click to expand...

It's very dependent on propagation conditions. In my other existence as a radio ham, I have, on rare occasions, had conversations on VHF frequencies over ranges of multiple hundreds of miles on a hand-held radio with an output of less than 5w. Under normal conditions, ten to twenty miles is more realistic.

For VHF frequencies, it's the low level atmosphere that counts, not the ionosphere as is the case for short wave. For unusually long distances you need a large area of high pressure with good stable weather. Listen on the various coast guard channels in the middle of summer during a long high pressure block and you will hear continental stations that are well outside normal range.
 
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