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

Looking at the ARRL Antenna book it seems that the angle of radiation is
pretty well fixed on the type of antenna.
"Ian White G3SEK" wrote in message
...
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

Mike Coombes wrote:
Looking at the ARRL Antenna book it seems that the angle of radiation
is pretty well fixed on the type of antenna.

Talking about "the" angle (as if there was only one) is misleading
ourselves.

Every antenna has a *range* of angles over which it radiates (or
receives) the best. The aim is to make that coincide with the *range* of
angles over which signals are likely to arrive.

This is made very clear in the 18th edition of the Antenna Handbook
onwards. It presents arrival angles as a statistical range of
probabilities, over a spread of possible propagation conditions.

If you have only one antenna, then obviously you try to make its very
best radiation angle coincide with the most *likely* angle of arrival.
But it's a game of chance. Occasionally the angle may be very different
from the most likely value, so you have to accept that you're going to
be some dB down... or dead in the water. And that is where having a
choice of different antennas really scores.


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