UHF radio range

Submitted: Friday, Nov 29, 2002 at 01:00
ThreadID: 2498 Views:1936 Replies:4 FollowUps:4
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On the way back from CSR a few months ago we managed to have a conversation with one of our vehicles at the distance of almost 300km. He was at the Sandfire roadhouse and we where just arriving in Broome. All this without a repeater.Must be the skip of the water. Has anyone had any similar experience?
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Reply By: Member - Trevor - Saturday, Nov 30, 2002 at 01:00

Saturday, Nov 30, 2002 at 01:00
Yes - we frequently had 200km from our GME in the flat country south of Alice. Supposed to be line of sight but I guess you can see a long way out there. Trev
AnswerID: 9149

Follow Up By: Old Soldier - Saturday, Nov 30, 2002 at 01:00

Saturday, Nov 30, 2002 at 01:00

Due to the earths curvature 200 km [even in flat country] is way beyond the line of sight.

Picking up UHF at those sorts of distance is just one of the many phenomena exhibited by radio.

Professional radio operators spend a lot of time learning radio and antenna theory, and thats exactly what it is - THEORY.

Sometimes what is exhibited in practice defies anything you may read in a textbook.

I have personal experience of UHF low wattage transmissions being received OVER 4,000km from the transmitter.

If you have the right contacts with the right equipment, these phenomena can quite often be predicted to a point.

Goran, it would have been an interesting experience for you. Something like that is always interesting.


FollowupID: 4584

Reply By: Bob Y. - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
Goran, Dennis probably summed up this phenomena?pretty well. We use UHF every day and often get many "phantom" transmissions at different times. Haven't had too many lately, because it's been too dry, but back a few years when it was raining regularly, it was nothing to have signals from up to 300 kms away. Read in a CB mag some years back where they were getting good transmissions from Perth to Melbourne, with Yagi type aerials.

The best times seeem to be after rain, when the change has past, and the atmosphere is clear. We often get signals that are 3-500 kms away. In 86-87, we were living around Gregory River south of Burketown, and often got signals from a station calling a property near Aramac. Never checked how far it was, but it was well past line of sight. Maybe we will be able to pick you up over in the west one day? Regards...
AnswerID: 9151

Follow Up By: Old Soldier - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
G'day Bob,

Yeah, it sure is interesting. As you may have gathered I used to a professional radio operator - on all things from the smallest man pack up to massive land based installations using satellite technology. It is theory, and nothing else.

To add to your interesting story, many years back when living in Singapore in my army days, we used to quite regularly pick up the sound channel of a Bangkok TV station. It used to occasionally break through on one of the weaker Malaysian channels we used to watch.

As for how far you can get if you really want to. When I was a the army School of Signals, the officer who taught antenna theory set up an experiment with an A510 portable man pack transveiver [you old blokes reading this will know it].

He designed a folded half wave dipole antenna for this thing. We erected it in the grounds of the Signals school, and attempted to communicate in both voice and morse with the SAS base in Karacatta WA. After about 4 hours we finally got through on both morse and voice.

The amazing thing was the power ouotputs - 500milliwatts on Morse and 200 milliwatts on voice.

As I said - theory [which sometimes works better than the book]

Goran, I agree with Bob - it would be nice to make a radio contact with you over here in Qld one day.

What do you do for a crust? you always seem to be in the bush you lucky bugger. My brother has a job like that over in WA. He is the Northwest WA manager of a company loosely aligned with the mining industry and based in Karratha. He spends most of his time in the Pilbara and Kimberly in his company provided GU Patrol. What a life.

Bob - aint the Gregory area a beautiful place?

That river has the sweetest water - I hope it stays that way with all the grey nomads camped on the banks near the pub. I was reading in the paper recently that some of them are doing "nasties" in the river. dirty old bastards.


FollowupID: 4587

Follow Up By: Goran - Monday, Dec 02, 2002 at 01:00

Monday, Dec 02, 2002 at 01:00
I work in a minning industry and live in Port Hedland. About 350km from Karatha. I do get around the bush fair bit , but nowhere near as much as i would like. I work shifts....4 on 4 off....plenty of time for everything.
FollowupID: 4616

Reply By: Bob Y. - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
Goran, Wrote the above at 3am,so missed a bit. That effect you experienced is called "ducting". Apparently it occurs when a layer of colder air is trapped between 2 hot layers, and the signal travels along the cold air. We have a repeater and often get signals from 3 or 4 other repeaters on same channel, during ideal conditions. catch you later...
AnswerID: 9154

Follow Up By: Old Soldier - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
Hey Bob, thats exactly right.

Ducting is also the only time I get channel 9 in this part of Qld.

Not only are we all praying for rain at the moment - I am missing the Bloody Poms being thrashed in the cricket :) :) :)

Wiosh it would rain so I could watch today - mumble mumble mumble

FollowupID: 4588

Reply By: Member - Nigel - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
Ducting is caused by a tropospheric inversion, very similar process to what causes fog. I remember once a radio station in Ayr was wiped out by a radio station in Innisfail (350km away) because both their links (studio to main transmitter) were on the same UHF frequency.
AnswerID: 9157

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