Musings on tropo

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The VK-VHF mailing list aims to serve the community of radio amateurs and others interested in the technologies and techniques of operating on the amateur bands from 50 MHz and up, with a particular focus on weak-signal or long-distance working and propagation.

Unfortunately, every time a group of enthusiasts get together on a forum or mailing list, politics ensues as every contributor has strongly-held, differing opinions. It’s been my experience that in any given specialty, including my own profession, a small minority of participants have failed to learn the requisite social skills involved in communicating properly in pursuit of purely selfish agendas. This list is no different in that regard. Having being a subscriber since 2009, I am pleased to announce that this list has been largely free of inflated egos for the last twelve months or so.

Let’s get some diverse views on tropo in Australasia…

The Tropo across the Australian bight is interesting. I often take note of that occurrence and then watch it settle across the pond afterwards. Not always, but a good indicator.

Steve ZL1TPH

Of course, to state the bleeding obvious, summer time is best. It is the weather conditions that really determine the propagation – a High nestled in the Bight is a great start but there’s more to it! Wally Howse VK6KZ wrote a great article on the subject:

WA weather chart

VHF, UHF & Microwave Propagation & the Great Australian Bight

Dave VK3HZ

I can remember talking with Kerry [Adams VK5SU from Ceduna] at the time about how he could regularly work the guys in Albany and Esperance like locals along the coastal duct, whereas the Adelaide stations would be hearing nothing.

Peter VK3QI

VK-VHF Digest, Vol 48, Issue 10 Feb 2012

It is usually assumed that being on mountain tops will get you further – that is not always the case. Those who have tried to operate along the Great Dividing Range from VK3/VK2/VK4 have often found shielding effects from population centres – it is REALLY difficult to find accessible spots in the Great Dividing range that provide good takeoff in more than one direction.

Quite often one can be too high and miss ducting. We had a documented example the last Summer FD between MtTassie VK3WRE/p and McLaughlin’s Lookout VK3ER/p a distance of 230 kms. Perfect signals (as one would expect) on 1.2, 2.4, 3.4 and 5.7 Ghz but absolutely nil on 10Ghz – (above the duct) – three hours later the duct had lifted and 10Ghz was as good as the lower bands – this is all on video see:

Is a 10 Ghz qso over 200 kms between two mountain tops easier than a 50 km qso between a mountain top and someone in an urban area shielded by buildings etc.? Does the same degree of difficulty apply to lower frequencies where urban obstructions are far less inhibiting?

One of the peculiarities of the Australian continent is the propensity for high pressures to develop and remain stationary over large areas of the continent. Not necessarily just the Great Australian Bight or the Tasman sea. An example of this occured last Summer when a large duct developed over western NSW and north eastern South Auatralia which enabled stations in northern NSW to work across to Adelaide on 1296 for a significant period of time when south of the Great Dividing Range there was limited propagation.

Peter VK3QI

VK-VHF Digest, Vol 40, Issue 15 Jun 2011

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