How far with VHF?

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Gemini4
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How far with VHF?

Post by Gemini4 »

Might be a bit of a thick question..but I was wondering how far you could get on vhf using repeaters?.
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ch25
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Re: How far with VHF?

Post by ch25 »

Worldwide.
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thedeerhunter270
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Re: How far with VHF?

Post by thedeerhunter270 »

I always thought it was line-of-sight plus a third. But like Chris says, in the right conditions much further.
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Re: How far with VHF?

Post by Metradio »

As has been said worldwide - but through networked repeaters..
Through a single repeater, your distance to the repeater plus line of sight + 1/3rd from the repeater...
Through multiple radio repeaters, ISTR the maximum being 12 hops before the signal becomes unusable..

Search "Backbone"... :idea:

http://www.subbrit.org.uk/rsg/features/ ... ndex.shtml


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Last edited by Metradio on 09 Mar 2018, 13:09, edited 1 time in total.
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Gemini4
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Re: How far with VHF?

Post by Gemini4 »

Will it also depend on antenna and power?.
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Re: How far with VHF?

Post by Metradio »

Yes, plus frequency...
The international Space Station can be worked on a 2M 2 Watt handheld on it's own antennta when the ISS is within range (LOS+1/3)...

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Gemini4
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Re: How far with VHF?

Post by Gemini4 »

Well thanks for the replies.
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Re: How far with VHF?

Post by paulears »

where on earth has this magic 1/3rd figure come from? Coverage from any location is dependent on topography. The idea of a set figure doesn't work.
distance to the repeater plus line of sight + 1/3rd from the repeater...
Unless all my education is totally wrong, it's simply signal strength at the antenna - and that's a function of the path loss, which can be predicted with software that has topographical data in it.
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Re: How far with VHF?

Post by Metradio »

Line of sight + a third is something I picked up about 50 years ago, do you know what ? As a rule of thumb it does work, on top of a mountain or on a flat plain.. If there is stuff in the way - well common sense comes into play..

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Re: How far with VHF?

Post by Tigersaw »

I did some (AM) VHF trials for a new ATIS at Southampton airport, with 25w from ground station the aircraft could still pick it up at 6000ft around Manchester
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Re: How far with VHF?

Post by Metradio »

A toy for people to play with:
http://www.heywhatsthat.com/profiler.html

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Re: How far with VHF?

Post by paulears »

metroradio - I still don't understand? what is 'line of sight' in this context - As tigersaw says, from the ATIS to an aircraft is line of site, and ground to the space station is line of sight, but is there a line of site at all to a repeater that makes sense? Maybe if it's on a high block of flats - but line of sight at ground level fails very quickly - line of sight for a repeater could be hundreds of yards in some cases, so this 'rule' fails in any urban location because there isn't one! Not even with binoculars.
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Re: How far with VHF?

Post by Metradio »

It was something I learned in the army when setting up temporary VHF links, where vehicle location was a mixture of good radio location and natural camouflage, plus the question of where the enemy would expect you to be. So the LOS +1/3 was used as a rule of thumb together with a common sense appreciation of intervening terrain and ground clutter.. Sometimes you did not have the luxury of setting up links in advance and had to work off of maps - no computers to work it out for you.. The LOS +1/3 expectation was under optimum conditions, everthing in between became a variable, this is where common sense and experience are heavily relied upon..

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Re: How far with VHF?

Post by VintageTin »

paulears wrote: 10 Mar 2018, 08:50 metroradio - I still don't understand? what is 'line of sight' in this context - As tigersaw says, from the ATIS to an aircraft is line of site, and ground to the space station is line of sight, but is there a line of site at all to a repeater that makes sense? Maybe if it's on a high block of flats - but line of sight at ground level fails very quickly - line of sight for a repeater could be hundreds of yards in some cases, so this 'rule' fails in any urban location because there isn't one! Not even with binoculars.
When talking "Line of sight", it means the ground. The signal will be degraded by the presence of buildings, but it does rattle around them somewhat, depending how close those buildings are to you. If you live in a bungalow next to a tower block, you will have more of a problem than if the tower block half way between you and the other station.
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Re: How far with VHF?

Post by paulears »

exactly - so what is line of sight, when you can't see it? A mile? 10 Miles? You can't have a formula to work to with an unknown variable?
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