Cecil Moore wrote:
John wrote:
Can someone tell me please an easy way to calculate the optimum angle
of radiation from a transmitting antenna over a given path on the HF
bands (160m - 10m)?
OK, I guess its all to do with the height of the reflective layer in
play and the distance of the QSO but I'd really appreciate some clues
to how to work this out.

Try the propagation chapter in the ARRL Antenna Book.

That would be a very good introduction to modern software like W6ELPROP.
What it teaches you is that angles of arrival vary considerably, even
for one given path, for reasons ranging from time of day to time in the
11/22-year sunspot cycle.

Remember that the F-layer is constantly changing height, especially if
it's around around dawn and dusk at one of the reflection points. This
means that at certain times the propagation has to 'flip' from say
3-hop-F to 4-hop-F, so the angle will flip too. And don't forget the
E-layer, if that's there too.

W6ELPROP will actually tell you what propagation modes are the most
likely at various times of day... and the reality is *much* more
complicated than the simple pictures shown in older books.

The ARRL Antenna Book does rather assume that you can put up any antenna
you can dream of; in which case, it will help you design the optimum
system. Ideally, the antenna needs to be able to adapt to the needs of
the moment.

But for most of us, it's much simpler than that. We can never achieve
the low angles that are sometimes needed for some of the most important
paths, so it simply comes down to doing the best we can. "Adaptability"
comes down to possibly having a second-choice antenna... which at
certain times may turn out to be better.

But even if we can't actually *do* anything about it, it's better at
least to understand that arrival angles (or conversely, optimum launch
angles) are actually very variable.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek