Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.

Hope this helps in understanding what occurs from bending the radials
downward.

Walt, W2DU

Walter Maxwell wrote:

The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.

Not to mention that's a damn handy angle when you need the
radials to double as guy wires...

The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.


Not to mention that's a damn handy angle when you need the
radials to double as guy wires...


Not to mention further, it helps keep birds off!!



Ed

Such an excellent and succint didactic exposition deserves
wider recognition.....

"Walter Maxwell" wrote in message
...
Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.
Hope this helps in understanding what occurs from bending the radials
downward.
Walt, W2DU

On Tue, 11 Jan 2005 08:50:27 -0000, "Airy R.Bean"
wrote:

Such an excellent and succint didactic exposition deserves
wider recognition.....

Whilst an interesting contribution, for which thanks are due to the
OP, many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before? Can't you write in
excellent, succinct, and/or didactic fashion? Or have you just gone up
the learning curve?

"Walter Maxwell" wrote in message
.. .
Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.
Hope this helps in understanding what occurs from bending the radials
downward.
Walt, W2DU


--
from
Aero Spike

On Tue, 11 Jan 2005 09:41:57 +0000, Spike
wrote:
many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before?

Hi OM,

Much the same faint complaint could be lain against you, which is to
say, seeing as you "knew this" why didn't you explain it as well?

This is simply stealing Walt's thunder. It takes only once, and that
moment passed.

73's
Richard Clark, KB7QHC

On Tue, 11 Jan 2005 08:35:36 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 09:41:57 +0000, Spike
wrote:
many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before?

Hi OM,

Much the same faint complaint could be lain against you, which is to
say, seeing as you "knew this" why didn't you explain it as well?


Simple. The context for the information posted is that Bean held a VHF
licence for many years before getting the HF licence. In my own case,
I have never been interested in VHF, confining myself to HF and
ground-mounted verticals, where the option of sloping any radials is
not available. I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Further, my original post on this also said "...an interesting
contribution, for which thanks are due to the OP...", which you
snipped.
--
from
Aero Spike

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

My 1978 Antenna Handbook by Orr & Cowen, page 92, references drooping
radials at a 45 degree angle for a better impedance match, raising the
gain of the ground plane antenna by about 0.5 decibel over the normal
configuration.

'Course Walt probably preceeded those guys :-)

bob
k5qwg

On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

The reference I had in mind was an article or item in the RSGB's
flagship journal (Radio Communication at that time?) which had a
picture of the two-radial vertical and a description of what happened
when the radials were progressively angled below the horizontal. This
must have been 15+ years ago. I can't recall now if it referenced any
of the said gentlemen's works, but the parallels are there.
--
from
Aero Spike