VHF Range - What's Your Record?

demonboy

demonboy

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We had a successful crossing from Turkey to Egypt and are now making our way down the Suez Canal. As we made our way through the Delta region in the Eastern Med I made contact with our friends aboard 'Full Flight' via VHF. It took us a few moments to plot our respective positions and we found, to our surprise, that they were over 100 miles away!

Our recent aerial installation using RG213 cable definitely improved our reception around the Turkish coast this year, and we've been relaying for other boats on the rally due to our excellent VHF reception, but I have to say I was very impressed with 100 miles.
 
demonboy said:
We had a successful crossing from Turkey to Egypt and are now making our way down the Suez Canal. As we made our way through the Delta region in the Eastern Med I made contact with our friends aboard 'Full Flight' via VHF. It took us a few moments to plot our respective positions and we found, to our surprise, that they were over 100 miles away!

Our recent aerial installation using RG213 cable definitely improved our reception around the Turkish coast this year, and we've been relaying for other boats on the rally due to our excellent VHF reception, but I have to say I was very impressed with 100 miles.
Click to expand...

I thought VHF was 'line of sight' 26 nm to the horizon plus mast height of both transmitter/receivers?

Were you on a big sand hill at the time.
 
I've clearly heard Swansea CG from the Solent a couple of times, didn't try to transmit to them!

Would love to know how that's possible - can the signal bounce off clouds? Or can Swansea accidentally transmit via Solent's?
 
MarkieMarkMark said:
....Or can Swansea accidentally transmit via Solent's?
Click to expand...
Yes they can, all the CG comms can be networked to any of their locations.
I was near Thames CG once (off Walton, Essex), and suddenly was picking up Solent loud and clear. After a while, I called up Thames and asked them about it. Atmospheric conditions, they said. Funny thing was, though, that I never heard Solent after that!
 
oldsaltoz said:
I thought VHF was 'line of sight' 26 nm to the horizon plus mast height of both transmitter/receivers?

Were you on a big sand hill at the time.
Click to expand...

Perhaps it's different in the southern hemisphere but hereabouts the horizon is about 3 miles away at sea level, so you can achieve line-of-sight communication between masthead aerials of maybe 20 miles, more to a shore station with a big antenna tower on top of a hill or if you have a very big mast. I think atmospheric conditions that allow greater distances occur quite a lot, I've certainly heard Clyde CG from over 50 miles away on the other side of the country at times. Someone will be along soon with a knowledgeable treatise on 'tunnelling' or 'ducting' or some word like that....
 
I've spoken to Falmouth Coastguard whilst we were half way across Biscay; about 200 miles. Exceptional high pressure at the time helped.
 
demonboy said:
We had a successful crossing from Turkey to Egypt and are now making our way down the Suez Canal. As we made our way through the Delta region in the Eastern Med I made contact with our friends aboard 'Full Flight' via VHF. It took us a few moments to plot our respective positions and we found, to our surprise, that they were over 100 miles away!

Our recent aerial installation using RG213 cable definitely improved our reception around the Turkish coast this year, and we've been relaying for other boats on the rally due to our excellent VHF reception, but I have to say I was very impressed with 100 miles.
Click to expand...

There is an effect called trospheric ducting where VHF radio waves are bounced between two layers of the troposphere, and can increase the range to hudreds of miles.
Same effect as Summertime TV interference.
I have spoken to to Holland from Shetland using a 10 watt VHF radio and the aerial lying on the ground. Often associated with High Pressure regions.

Regards

Bob
Scotland
 
Yep:- high pressure. Heard Dover CG when in Helford, aerial about 14ft up, the old one that looks like a broomstick. I have an Icom handheld, secondhand 23 years ago, powered from a transformer, rigged to a home made 'slimjim' aerial (about 150ft off sea level) and I pick up Ushant traffic at times. Local ham has transmitted (from the Lizard) to Plymouth and received from Amersham with a slimjim.
 
demonboy said:
We had a successful crossing from Turkey to Egypt and are now making our way down the Suez Canal. As we made our way through the Delta region in the Eastern Med I made contact with our friends aboard 'Full Flight' via VHF. It took us a few moments to plot our respective positions and we found, to our surprise, that they were over 100 miles away!

Our recent aerial installation using RG213 cable definitely improved our reception around the Turkish coast this year, and we've been relaying for other boats on the rally due to our excellent VHF reception, but I have to say I was very impressed with 100 miles.
Click to expand...

Ducting in that part of the world is not uncommon and can allow VHF and radar to achieve far greater than line of sight ranges. In the Red Sea I can remeber tracking contacts on radar that were detected at 40 miles, tracked in to 0 where upon they zipped back out to 40 again and would be tracked in till they became visual at the normal 10 miles or so.
 
One of my students told me of three Shetland fishing boats having a VHF conversation between a boat north of Muckle Flugga, (the northerly turning point for all those who claim to have sailed around Britain) Fair Isle, and Peterhead. We often heard Norwegian VHF coast stations when on the east side of Shetland, but they were transmitting from relay stations on offshore platforms so the range was only around a hundred miles.

High pressure conditions can cause a wave duct between sea surface and a temperature inversion in the lower atmosphere. A similar effect known as supper refraction extends the range of radar signals and sub refraction reduces radar range by bending the signal up off the surface.

I'm not sure how tropospheric ducting will increase marine VHF range as the waves will be trapped within the duct so both transmit and receive antenna would also have to at the right altitude in the troposphere.
 
MarkieMarkMark said:
I've clearly heard Swansea CG from the Solent a couple of times, didn't try to transmit to them!

Would love to know how that's possible - can the signal bounce off clouds? Or can Swansea accidentally transmit via Solent's?
Click to expand...


There is a VHF switching centre and sometimes the lone watchkeeper for lots of coastline is in somewhere far removed....If he then presses the wrong switch for the area he thinks he is talking to heaven knows what record you might hear.

I have heard Oban Radio in the Forth and Aberdeen coastguard on the west coast however I suspect in both cases I was hearing the local transmitter which was being keyed remotely from elsewhere.
 
Chuzzlewit..and can anyone confirm..I believe AIS is received then rebroadcast,or relayed,by a dedicated shore apparatus. In fact it must be to include buoys out of position etc.
Some of the other posts are astounding,am I to disbelieve the old line of sight mantra for 156 Mhz? If not,what`s going on? And if we find out could it be deliberately repeated? (flippancy alert) A Nobel prize there for some sparky! good watch Jerry
 
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