chuck wrote:

Don't know from personal experience, but Les Moxon, author of HF
Antennas for all Locations, seems to believe it creates an advantage.
You might want to read his thoughts on that.


The advantages of which Moxon wrote are for *horizontal* polarization
only. If the antenna height above ground is correct, the ground
reflection can reinforce low-angle radiation in the downslope direction.

But Moxon also shows specifically that there are *no* such advantages
for vertical polarization. The ground-reflected ray is lost at a high
angle.


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

Hello, Ian.

Yes, I was a bit hasty in citing Moxon.

But thinking a little more about this I wonder. Intuitively, and looking
at Moxon's sketch, it would seem that the effect would be simply to
rotate the vertical pattern by the amount of the slope. Aiming the
pattern "down the slope" rather than "toward the horizon" does not seem
to be a necessarily worse situation as Moxon suggests. Wouldn't that
actually put more energy out toward the horizon?

Tilting a VHF ground plane antenna toward the horizon would be different
because the vertical pattern at zero degrees is not attenuated by ground
losses.

Chuck








Ian White, G3SEK wrote:
chuck wrote:


Don't know from personal experience, but Les Moxon, author of HF
Antennas for all Locations, seems to believe it creates an advantage.
You might want to read his thoughts on that.


The advantages of which Moxon wrote are for *horizontal* polarization
only. If the antenna height above ground is correct, the ground
reflection can reinforce low-angle radiation in the downslope direction.

But Moxon also shows specifically that there are *no* such advantages
for vertical polarization. The ground-reflected ray is lost at a high
angle.

chuck wrote:
Intuitively, and looking at Moxon's sketch, it would seem that the
effect would be simply to rotate the vertical pattern by the amount of
the slope. Aiming the pattern "down the slope" rather than "toward the
horizon" does not seem to be a necessarily worse situation as Moxon
suggests. Wouldn't that actually put more energy out toward the horizon?

That is true in principle, but the problem with a ground-mounted
vertical antenna is that the angle of maximum radiation is fixed in
relation to the ground. That means the angle of the slope has to be just
right, and in general it also needs to be very steep.

With a horizontal antenna, you can vary the angle of maximum radiation
by adjusting the height above ground. That makes it easy to apply the
technique over a wide range of quite moderate slope angles, using quite
modest antenna heights.

Changing the subject slightly, hams have become over-conditioned into
wanting a "low" angle of radiation. It's true that we generally do need
more radiation at lower angles than we can easily achieve; but until
recently, we haven't had the information to understand what angles of
radiation we actually *do* need.

Modern HF propagation programs give us that information. Not
surprisingly, the optimum angle varies according to the path, the number
of hops involved, the heights of the respective layers and the
ionization levels... and hence the optimum angle also depends on the
time of day, the season, and the year in the sunspot cycle. Recent
editions of the ARRL Antenna Handbook analyse this problem in some
detail, and show that "lowest possible angle" is not always the best
objective if you're aiming to cover all possible cases.


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

From decades of looking at optimum take-off-angles (TOA) at HF for long
paths, I have found that TOAs are rarely above 12 degrees and only
occasionally below 2 degrees. This leads to the conclusion that if cost
were not an issue and one could only put up one horizontally polarized gain
antenna (Yagi, LPDA, or such), the antenna should be 2 to 2.5 WL high. At
least one edition of the ARRL Antenna Book has the same conclusion.

A higher antenna starts to have nulls in the useful range of TOAs.

As usual, Ian has the right idea.

73 Mac N8TT


--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Ian White, G3SEK"

That is true in principle, but the problem with a ground-mounted
vertical antenna is that the angle of maximum radiation is fixed in
relation to the ground. That means the angle of the slope has to be just
right, and in general it also needs to be very steep.

With a horizontal antenna, you can vary the angle of maximum radiation
by adjusting the height above ground. That makes it easy to apply the
technique over a wide range of quite moderate slope angles, using quite
modest antenna heights.

Changing the subject slightly, hams have become over-conditioned into
wanting a "low" angle of radiation. It's true that we generally do need
more radiation at lower angles than we can easily achieve; but until
recently, we haven't had the information to understand what angles of
radiation we actually *do* need.

Modern HF propagation programs give us that information. Not
surprisingly, the optimum angle varies according to the path, the number
of hops involved, the heights of the respective layers and the
ionization levels... and hence the optimum angle also depends on the
time of day, the season, and the year in the sunspot cycle. Recent
editions of the ARRL Antenna Handbook analyse this problem in some
detail, and show that "lowest possible angle" is not always the best
objective if you're aiming to cover all possible cases.


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

Don't know from personal experience, but Les Moxon, author of HF
Antennas for all Locations, seems to believe it creates an advantage.
You might want to read his thoughts on that.


The advantages of which Moxon wrote are for *horizontal* polarization
only. If the antenna height above ground is correct, the ground
reflection can reinforce low-angle radiation in the downslope direction.

But Moxon also shows specifically that there are *no* such advantages
for vertical polarization. The ground-reflected ray is lost at a high
angle.
--
73 from Ian G3SEK

==================================

Dear Ian, what has Moxon got to do with it?

Without personal experience how do you know you are not plagiarising and
further propagating old-wives' tales?

If you have personal experience do you need anybody else's support anyway?

Just state the facts on your own authority.

Or do authors all belong to the same masonic club which adds nothing to
veracity?

My only little axe is that I find it irritating when I read about quite
unnecessary references which add nothing but verbiage to the conversation.
Perhaps I'm funny or just impatient in that way.

But I'm sure you understand my non-technical interruption to this thread
with my appology. Reply not needed.

(PS: I have only vaguely heard of Moxon in these newsgroups. Never read him.
Not the slightest disrespect to him, or her, intended. But my own reference
bibles are restricted to Ohm, Ampere and Volta.)
----
I think I can still call you my Internet friend. ;o)
----
Yours, Reg, G4FGQ

Reg Edwards wrote:
Don't know from personal experience, but Les Moxon, author of HF
Antennas for all Locations, seems to believe it creates an advantage.
You might want to read his thoughts on that.


The advantages of which Moxon wrote are for *horizontal* polarization
only. If the antenna height above ground is correct, the ground
reflection can reinforce low-angle radiation in the downslope direction.

But Moxon also shows specifically that there are *no* such advantages
for vertical polarization. The ground-reflected ray is lost at a high
angle.
--
73 from Ian G3SEK

==================================

Dear Ian, what has Moxon got to do with it?

He was the person who was being misquoted. In the first reply, I was
setting that record straight.

Without personal experience how do you know you are not plagiarising and
further propagating old-wives' tales?

Because, whatever else I read, I also do my own thinking.

If you have personal experience do you need anybody else's support anyway?

Just state the facts on your own authority.

Or do authors all belong to the same masonic club which adds nothing to
veracity?

Certainly not; most authors do value a cross-check on their own thinking
- and above all, a cross-check against reality.

I certainly do, because it's how I was trained.

The value of the major academic textbooks is that most of them have been
in the public domain for decades, and available for critique and
cross-checking and correction in later editions. If your own findings
don't agree with the pool of knowledge that's already out there, you'd
better have some strong reasons to hand.

In this respect, all amateur radio publications are in a lesser league.
They are still going through the process of critique and technical
clarification - marvellously accelerated by the Internet in recent years
- but they're not there yet.

(PS: I have only vaguely heard of Moxon in these newsgroups. Never read him.
Not the slightest disrespect to him, or her, intended.

Perhaps you should: Moxon was a lot like you in his methods and his ways
of thinking.

But my own reference
bibles are restricted to Ohm, Ampere and Volta.)

All three of whom are conveniently not available for comment.

----
I think I can still call you my Internet friend. ;o)
----

For about 15 hours out of 24, I reckon.

But anytime after your first glass of the evening, and before my first
cup of coffee the next day, don't push your luck :-)


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