Setting aside the mistaken belief that even licensees of several years'
standing
have that a short antenna will radiate all the power that is fed to it, even
long
antennae do not do that!

Consider the terminated and very-directional Rhombic with legs that are
several
wavelengths long; the reason for the termination is to absorb the power that
does not
get radiated and to prevent it being reflected and so making the Rhombic
bi-directional
instead of uni-directional..

Also, consider the following, if shorter (than the Rhombic) antennae radiate
all the
power fed to them, there would be no advantage to extending the length of
any antenna
because the shorter bit would have radiated all the power, and there'd be
nothing left
for the longer bit to radiate.

As it is short (and unterminated) antennae only radiate a small proportion
of the power that
is fed to them, and that which is not radiated is refelcted back to the feed
point considerably
out-of-phase with the incident power and so presenting a very reactive
impedance. (Yes, OK,
on the way back from the reflection, a bit more might get radiated, but I
suspect that the
out-of-phase wave affects the EM fields thereby reducing the radiative
capability)

On 10/26/2014 7:22 AM, gareth wrote:
Setting aside the mistaken belief that even licensees of several
years' standing have that a short antenna will radiate all the power
that is fed to it, even long antennae do not do that!

You are correct. Antennas have some loss as do all things.

Consider the terminated and very-directional Rhombic with legs that
are several wavelengths long; the reason for the termination is to
absorb the power that does not get radiated and to prevent it being
reflected and so making the Rhombic bi-directional instead of
uni-directional..

A rhombic antenna is not a short antenna. It is terminated because it is
designed to be a traveling-wave antenna and not to be a standing-wave
antenna. Please do not compare apples and airplanes.

Also, consider the following, if shorter (than the Rhombic) antennae
radiate all the power fed to them, there would be no advantage to
extending the length of any antenna because the shorter bit would
have radiated all the power, and there'd be nothing left for the
longer bit to radiate.

See my statement above. A rhombic might not radiate all the power fed to
it. As you say, it might be terminated by a resistance. However the
current in the rhombic will cause radiation from the wires with great
efficiency. The purpose of the rhombic is directionality, not efficiency.

As it is short (and unterminated) antennae only radiate a small
proportion of the power that is fed to them, and that which is not
radiated is refelcted back to the feed point considerably
out-of-phase with the incident power and so presenting a very
reactive impedance. (Yes, OK, on the way back from the reflection, a
bit more might get radiated, but I suspect that the out-of-phase wave
affects the EM fields thereby reducing the radiative capability)

The hallmark of a rhombic is that is long compared to the wavelength of
operation in order to achieve directionality (that is, gain in a
particular direction).

If you wish to discuss the difference between standing-wave antennas and
traveling-wave antennas, I would first suggest you learn the difference
between the two so that you can carry on an intelligent dialog.

Was my response to you abusive?

John S wrote in :

The hallmark of a rhombic is that is long compared to the wavelength of
operation in order to achieve directionality (that is, gain in a
particular direction).


It's totally new to me. I just looked at Google images for a few minutes.
Nice looking constructions. The thing that struck me most was your
description of directionality, non-resonance (at lest, not standing wave),
long compared to wavelength, and termination by a resistance. All these
things can be said of a Bevarage too, but they're obviously very different
too. I don't know what the relation is.

Lostgallifreyan wrote:
John S wrote in :

The hallmark of a rhombic is that is long compared to the wavelength of
operation in order to achieve directionality (that is, gain in a
particular direction).


It's totally new to me. I just looked at Google images for a few minutes.
Nice looking constructions. The thing that struck me most was your
description of directionality, non-resonance (at lest, not standing wave),
long compared to wavelength, and termination by a resistance. All these
things can be said of a Bevarage too, but they're obviously very different
too. I don't know what the relation is.

http://en.wikipedia.org/wiki/Rhombic_antenna

http://www.w8ji.com/rhombic_antennas.htm

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.

Otherwise people these days use log-periodics for better performance
and a lot smaller footprint.


--
Jim Pennino

wrote in :

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.


Ok, that rules me out right there. I can maybe manage a long wire laid out
temporarily, but for large scale that's about it for me.

Lostgallifreyan wrote:
wrote in :

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.


Ok, that rules me out right there. I can maybe manage a long wire laid out
temporarily, but for large scale that's about it for me.

Decades ago I was affiliated with an Army MARS station that had inherited
a WWII rhombic array of 4 antennas for 360 coverage that worked fairly
well from about 5 MHz and up.

The thing seemed to be a lightning magenet during thunderstorm season
and sections of the wire that had been vaporized required regular
replacement.

Eventually the Army decided it has better use for the nearly square
kilometer of land the thing took up and replaced it with a log-periodic.

The log-periodic was several dB better, both transmit and receive, in
part because there was no longer the 50% termination resistor loss.



--
Jim Pennino

In article ,
Lostgallifreyan wrote:

It's totally new to me. I just looked at Google images for a few minutes.
Nice looking constructions. The thing that struck me most was your
description of directionality, non-resonance (at lest, not standing wave),
long compared to wavelength, and termination by a resistance. All these
things can be said of a Bevarage too, but they're obviously very different
too. I don't know what the relation is.

There's a nice discussion of various traveling-wave antennas in
Laporte's classic "Radio Antenna Engineering" text.

http://snulbug.mtview.ca.us/books/Ra...naEngineering/

(David Platt) wrote in news:hk20ib-
:

http://snulbug.mtview.ca.us/books/Ra...naEngineering/

Thanks, that might be a way in for me. My eyesight won't stand a lot these
days, so concise is good, which that one is.

Lostgallifreyan wrote in
:

concise is good, which that one is.


I might be wrong about that. I really do need quick guides these days, my
days of long reading are long gone, it physically hurts now even when I can
do it at all.

En el artículo , John S
escribió:

Was my response to you abusive?

He won't have liked it, ergo, yes.

--
(\_/)
(='.'=)
(")_(")