Myths and Legends of Antennae
 

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)

Myths and Legends of Antennae
 

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?

Myths and Legends of Antennae
 

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!

Ignoring the nonsense about licensees and looking at what physicists have
to say about antennas, we find that all antennas radiate all the power
applied to them minus any resistive loss.

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.

A ridiculous conclusiong that totally ignores both antenna pattern and
the practical issues involved in feeding very short antennas.

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)

All a giant pile of babbling, confused nonsense that shows a total lack
of understanding of how antennas work.



--
Jim Pennino

Myths and Legends of Antennae
 

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.

Myths and Legends of Antennae
 

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

Myths and Legends of Antennae
 

On 26/10/14 17:44, wrote:
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!

Ignoring the nonsense about licensees and looking at what physicists have
to say about antennas, we find that all antennas radiate all the power
applied to them minus any resistive loss.

Which is exactly what was posted by those who posted correct inputs said.

As usual, Evans is posting malicious nonsense.


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.

A ridiculous conclusiong that totally ignores both antenna pattern and
the practical issues involved in feeding very short antennas.

He lacks even a grasp of the most basic antenna theory.


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)

All a giant pile of babbling, confused nonsense that shows a total lack
of understanding of how antennas work.


One of his standard ploys is to utter a load of such techno-nonsense.
Another is to hurl abuse. He has less pleasant ploys which, hopefully,
you will be spared.

Myths and Legends of Antennae
 

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/

Myths and Legends of Antennae
 

"Brian Reay" wrote in message
...
As usual, Evans is posting malicious nonsense.

Once again, you post gratuitous abuse but without venturing a technical
contribution yourself


He lacks even a grasp of the most basic antenna theory.

Once again, you post gratuitous abuse

One of his standard ploys is to utter a load of such techno-nonsense.
Another is to hurl abuse. He has less pleasant ploys which, hopefully, you
will be spared.

Once again, you post gratuitous abuse

So, M3OSN, are you having a hard time this weekend which has resulted in you
lashing out in all directions in every NG that you frequent?

Myths and Legends of Antennae
 

"Brian Reay" wrote in message
...

He has less pleasant ploys which, hopefully, you will be spared.

Are you, perhaps, referring to the precedent that you set in 2005 to
threaten
the liberties and livelihoods of those who did no more than to openly
disagree with you
on Usenet by sending for them to be arrested by the ploddery?

Did it not occur to you that your victims could end up getting the sack from
their jobs when you did that?

Myths and Legends of Antennae
 

En el artículo , John S
escribió:

Was my response to you abusive?

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

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

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

(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.

Myths and Legends of Antennae
 

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.

Myths and Legends of Antennae
 

Lostgallifreyan wrote in
:

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.


Well, it's a neatly made copy, but a huge tome, and I think maybe I got very
lucky in hitting one paragraph by accident, paraphrsed so:
"A rhombic antenna is only efficient when matched with the propogation medium
for specific frequency". In opther words, a good plan for transmission
efficiently in some direction at some frequency, but well beyond my scope for
quick experimental listening efforts.

Myths and Legends of Antennae
 

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

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

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


Thanks, I'll look at those a bit next time I can see well enough to read
much. Even the name is new to me right now.. :)

What I'm wondering is shy so much current discussion of whombic antennas at
all. I try to follow the tech posts because short repeats of good info may be
my best shot at absorbing it efficiently, but I'm not sure how rhombics got
such repeated notice.

Someone is attempting to make some sort of point by comparing apples and
strawberries.

The rhombic was a big deal in it's day back when huge, empty areas were
readily available and better antennas had not yet been invented.


--
Jim Pennino

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

The rhombic was a big deal in it's day back when huge, empty areas were
readily available and better antennas had not yet been invented.


I like apples and strawberries, but I'll not go into it. :)

I had a very quick look at log-periodic antennas before I sleep. That looks
like a much more practical notion to me. I guess practical DIY might still be
limited to shorter wavelengths, but it looks like a neat, compact and solid
antenna design, ideally suited to anyone with some accurate tooling and a
need for directivity combined with a relatively broad bandwith reducing need
for adjustments. Would it be a contender against a tuned magnetic loop for a
beginner's experiment?

Like all things in life it is a trade off of various things.

The accuracy requirement, at HF anyway, is not that bad and there are
LOTS of plans for DIY log periodic antennas out there.

Upside: Basically frequency independant (over a range), all metal
construction, can directly match 50 Ohms, and gain can be increased
by increasing the number of elements and making it longer.

Downside: A high gain antenna can be quite large, require a lot of
expensive aluminum, be quite heavy and like any beam needs a tower
and a rotor.

Since it is truely frequency independant, for certain uses, like military
that could be operating on any frequency, it is an almost ideal solution.

For hams that are constrained to bands, something like a hex beam
might be a more economical solution.

Your call.


--
Jim Pennino

Myths and Legends of Antennae
 

On 10/26/2014 5:01 PM, gareth wrote:
"Brian Reay" wrote in message
...

He has less pleasant ploys which, hopefully, you will be spared.

Are you, perhaps, referring to the precedent that you set in 2005 to
threaten
the liberties and livelihoods of those who did no more than to openly
disagree with you
on Usenet by sending for them to be arrested by the ploddery?

Did it not occur to you that your victims could end up getting the sack from
their jobs when you did that?




You mean like you purposefully tried to get him sacked for things he did
not do - and got docked for it?

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

Downside: A high gain antenna can be quite large, require a lot of
expensive aluminum, be quite heavy and like any beam needs a tower
and a rotor.

Since it is truely frequency independant, for certain uses, like military
that could be operating on any frequency, it is an almost ideal solution.


It does sound like it might be viable for portable use, carried in a backpack
to a hilltop. Probably not so good in my back yard though. :) Too many
buildings, too many things out there already, 12 solar panels on various
mounts, one tall whip, an FM dipole. I can maybe get an extra longwire out
there but that's about it now.

For VHF/UHF, but not for HF.

You do understand that a log periodic is a series of 1/2 wavelength dipoles
from the lowest to highest frequency of interest?

A "small" log periodic that will cover 20 to 10 M will have a boom about
12 feet long and the longest element will be close to 40 feet long.



--
Jim Pennino

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

You do understand that a log periodic is a series of 1/2 wavelength dipoles
from the lowest to highest frequency of interest?


I do now. :) Point taken, this is not a portable thing... I looked very
briefly last night before sleep, my (wrong) assumption was that the elements
were basically directors using a log scale to compress the effective result
into a smaller space... I didn't realise that each was a separate normal
sized 1.2 wave dipole.

Well, almost...

The longest element is 1/2 wave at a frequency slightly below the lowest
frequency and the shortest element is 1/2 wave at a frequency slightly
above the highest frequency.

The taper in the element lengths is described by a log function.

The total number of elements and the boom length effect both the gain and
"flatness" of the SWR over the frequency range.



--
Jim Pennino

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

The total number of elements and the boom length effect both the gain and
"flatness" of the SWR over the frequency range.


I can sort of see why the military would like it. Given their resources, it
could be used to rapidly find direction and frequency for many transmissions,
one after another, with no immediate need to co-ordinate a triangulation
effort. Though I suspect that locating sources isn't their primary reason for
using one.

Correct; they are used because the military is not constrained to discreet
bands like hams and it is much simpler to erect one antenna and tower
to cover a wide frequency range, though HF global comm is less and less
used by the military these days as everything is going encrypted space based.

Short range tactical comm still uses a lot of HF, but the antennas there
are usually whips with autotuners at the base.


--
Jim Pennino

Myths and Legends of Antennae
 

Myths and Legends of Antennae
 

Lostgallifreyan wrote:
wrote in :

HF global comm is less and less
used by the military these days as everything is going encrypted space
based.


And, I suspect, by policemen. :) No fun stuff on the edge of the FM broadcast
band these days...

Public service is mostly going to VHF/UHF trunked systems.

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


--
Jim Pennino

Myths and Legends of Antennae