Ridiculous range on VHF?

[defizr]

I used to be a radio officer in the merchant navy and we often picked up Cape Town/ZSC on ch16/156.8MHz 600 miles up the west coast of Africa. It's ducting as an3 says.

Edited to read "west" rather than "east". Good job I wasn't responsible for navigation

[FokkerInYour12]

Why we can't we have more discrete frequencies?

Having a scratchy transmission from 100NM away isn't enhancing my situational awareness at all.

Surely there's enough frequencies at .25Mhz intervals to do this?

[Hasherucf]

tropospheric ducting. It's covered in the radio basics casa exams. Exam code WA

[cowl flaps]

Most times the tropospheric ducting occurs during the peak of the 11 year sun spot cycle.

[WAC]

"Skip" is the common term for these bounced transmissions. The weird thing about them is that as they are due to a "bounce" off the ionosphere, stations closer to the originating point won't be able to pick them up as they are under the bounce.
Conditions more conducive to skip happen at night and I spent many a night parked atop Mount Sugarloaf talking to some places at huge distances, even sometimes o/s on a good old single side band CB radio.

Apparently the conditions can be predicted (related to solar activity) and the amateur radio enthusiasts use it to advantage to set personal records for long distance coms.

[poteroo]

In the 60's it wasn't unusual to hear Cairns TWR on 118.1 while operating out of Port Moresby. Bit of a wake-up to hear someone cleared for 15/33 instead of the 14/32 we were used to. Seemed to be more likely if you were down a bit lower, eg, 1500 ft and coastal E or W of Moresby.
happy days,

[Hobo]

What AN3 and tarq said. Google 'VHF ducting'

[Desert Flower]

If you're near water, the water will act as a ground plane. Not sure if it would work with VHF though, but it sure as hell used to work back in the days when I used to work skip on 27 megs!

DF.

[topdrop]

Look up sporadic E.
You can also get VHF reflections caused by a boundary between 2 markedly different air densities.
In FS, I can remember getting Moresby Tower on Townsville VHF and a fishspotter landed Echucha on the Port Lincoln VHF.

[parabellum]

When I lived in Abu Dhabi, at sea level, during the hot months we could listen to Dhahran (ARAMCO) broadcasting all day on VHF, Classic, Popular, Country and Western as well as the news, read by Larry Barnes, taken from the wires of UPI! That was well over 300 miles. Ducting, as mentioned already.

[Dexta]

I remember one of the Ham radio guys nearby used to do a "moon bounce", pump enough energy (around 1000w) with a good directional antenna at the moon and you could get Japan and sometimes the states. Can't remember the wavelength, definitely 10m or shorter though so VHF.

[AerocatS2A]

Bouncing off the ionosphere is more of an HF thing. It is also HF that is affected by sun spots. VHF ducting is from low level inversion layers.

[halas]

In the old days of TV sets only having 13 channels (Channel 5A..WTF?) used to get Adelaide TV stations from 300Km down the coast on a calm summer morning.

Also cancelling SAR with Darwin FIS after landing at Troughton Is. on VHF a few times too (550Km)

halas

[triadic]

In the good old days of FS, it was not uncommon for Derby to talk to Broome and Hedland on 122.1 - (almost the whole of WA was on 122.1 - make that most of FS Aust wide) comms were good quality but did not last for long - usually early morning or thereabouts.
Also one of the towers in Indonesia would often come thru on 118.3 at Darwin Tower.

[startingout]

Been a while but I do remember that Adelaide approach used to pick up Hamilton Victoria's CTAF at times. 124.8 rings a bell.

[601]

Cancelled SAR with CV on VHF while in the Windorah circuit back in the 70s. So it is not new.

[ZAZ]

TROPO

Its a result of tropospheric ducting, the signal normally would go through into outer space but is bent over or ducted down
examples are 124.2 innbound western sector into YPAD heard on 124.2 at YHML

The distance VHF can travel is huge hundreds and thousands of KM
Like from CALIFORNIA to HAWAII
MT GAMBIER to ESPERENCE

The link below will show VHF and UHF records made by ham operators not (VK2DIK) and as you can see a few hundred KM is no problem.

http://www.wia.org.au/members/record...s%20080801.pdf

[flyingins]

Westbound to Perth at FL360 this evening, just north and west of Esperance, ML CTR issues a change to 118.2. Upon first contact ADL Approach instructs me to check my frequency. 880NM away!

Once the mystery of why I was negotiating with two separate controllers was solved, I could still hear ADL Approach transmitting up to 1000NM away.

Read the books but never heard of it happening before. Kinda cool.

[greybeard]

Koolan Island to Karratha, unable to get Derby early morning.

Carnarvon to Meekatharra from the circuit in Carnarvon.

HF, Halls Creek to Isa as the only station in Aust. who could hear me.

All in the 70s when the world was a better place.

[Roj approved]

YBCG ATIS

So would this be the same reason you can get YBCG ATIS overhead YWLM at about FL300? (It's only for a very short time, 3mins max).

Can't get YBBN or YSSY coming south, but it's a reasonable signal for that distance. 290nm