VHF Range

[Piddy]

During my holiday I found a broken connection in the VHF aerial cable. There was some contact as the central conductor was touching the pin in the connector but was broken and (I suspect) when in use creating a high resistance connection.
This may explain why my Silva radio ceased working (as in no reception or transmission) after which I fitted a Simrad RD68. Prior to renewing the connector, the reception had been OK but not spectacular. I only became aware of a problem when 'ant' started flashing on the radio whilst transmitting.

Once I had attacked the connector on deck in Cherbourg (on a windy day - very hard to get a gas soldering iron hot enough!), the reception improved markedly. On the return home from Cherbourg I spoke to Solent Coastguard with excellent clarity from just outside the harbour giving me a range of some 55miles.

I know SC has a high transmitter and that VHF is fundamentally line-of-sight but I've never had transmitting range that good and now constantly hear coast guard reports from Dover through to Brixham and down as far as St Peter Port Radio whilst in Portsmouth harbour.

Over the years occasionally atmospheric conditions allow extended range but I get this range all of the time now with the consequence of constant babble on the speaker.

My mast is about 50' - do I assume everyone with a mast this height has this kind of range and that my old (non DSC) radio was a bit tired?

Cheers

 

[Bilgediver]

Yes VHF is line of sight but also atmospherics come into the equation and if there is a significant HIGH over the area then two stations may enjoy a much enhanced range.

I live in Edinburgh and in the summer have heard Rogoland (Norway)radio at my home which is alt 600 ft and I believe the transmitter is at 3000 ft.

Another effect that can come into play is something called ducting where the conditions create a duct and there are records of a a vhf signal from CApetown being heard in the UK and attributed to this phenomenon.

Mostly we are happy to get 25 miles so you are doing well if you get 50 miles every time 12 months of the year.

 

[Salty John]

VHf range is:
D = 1.4(root H1+root H2)
D is distance in NM, H is height in feet of transmitter and receiver.
D is actually the combination of transmitter distance to horizon plus receiver distance to horizon.
The theoretical multiplier is 1.23 but 1.4 is used for average conditions because you do get some 'bend' in the signal.
If your antenna is 60' up and the coastgueard antenna is on a hill at, say, 1000', your theoretical communication distance is 55 miles. Your system is working well!

 

[raquet]

My boat lives permanently in Cherbourg and when I connected my new VHF antenna I wondered how best to test it. I switched on and heard Solent CG very clearly. I thought that sufficient proof at least for reception. Since then I regularly hear Solent and listen to the weather forecasts just out of nostalgia.

 

[Marmalade]

Must have had some wierd atmospherics a couple of weeks ago - we picked up SOLENT coastguard from the R Blackwater!

Simon