Robert11 wrote:

a. Anyone have any idea if a receiving
Discone type of antenna is Polarized
horiz. or vert. ?

It is vertically polarized over its entire
frequency range.

b. Same question for a Scantenna ?

If it is installed as usually illustrated with
the elements vertical, then, yes, it too is
vertically polarized.

c. On VHF and UHF scanner freq's, are the
(typically vertical, I believe ?) transmitted
polarizations from Fire and PD transmitters
usually maintained over distances of, e.g.,
10 miles or so ? Or does "bounce", etc., tend
to totally de-polarize them ?

Land mobile and aircraft radios almost invariably
use vertically polarized antennas. That wave
polarization is generally maintained under conditions
of reflection and refraction over short- and long-
distance paths. For polarization rotation to occur
during propagation, the medium generally must be
birefringent (eg: the ionosphere). This rarely occurs
with terrestrial waves.

d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?

The usual figure one sees bandied about is 20 dB.

e.g., for a rubber-duckie scanner antenna ?

There's an additional penalty of 20 dB imposed on
any antenna that has the word "duckie" in its name.
;-) ;-) ;-)

Jim, K7JEB

d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?

The usual figure one sees bandied about is 20 dB.

I've seen it quoted as "up to 30 dB". That's probably under ideal
(or ideally-bad) conditions, though.

e.g., for a rubber-duckie scanner antenna ?

There's an additional penalty of 20 dB imposed on
any antenna that has the word "duckie" in its name.
;-) ;-) ;-)

Heh. Yeah. Last weekend, my partner-in-repeater-crime and I ran some
simple outdoor-range tests on a few 2-meter beams, using an HP signal
generator and HP spectrum analyzer. We used a quarter-wave whip,
mag-mounted on a sheet of steel, as the reference antenna.

A two-element HB9CV beam was around 8 dB better than the reference
antenna, with a front-to-back ratio of 6-8 dB.

An Elk log-periodic 6-element beam measured out as quite similar to
the HB9CV (but has a lower SWR across the band) - 8 dB up, and about 7
dB front-to-back.

A 3-element Yagi made out of PVC and steel measuring tape segments,
designed for foxhunting, was 9-10 dB up and had about a 20 dB
front-to-back ratio at its deepest null.

Rubber duckies? Ugh. A Yaesu helically-wound duck was around 10 dB
worse than the reference antenna. An RD-9 "high gain" base-loaded
2-meter/440 superflexible antenna was around 12 dB worse than the
reference antenna.

I'd always heard that rubber duckies were actually rubber dummy loads.
Now I've actually seen the results for myself. Yeech.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Here is a reference to a technical look at short loop antennas from the
1950's by Wheeler.

H. A. Wheeler, "Fundamental Limitations of Small Antennas", Proc. IRE, vol.
35, pp. 1479-1484

This is can found in a technical library with access to the IEEE
publications web site (e.g. university or military tech library)


Thane-fer
Homer


"Dave Platt" wrote in message
...
d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?

The usual figure one sees bandied about is 20 dB.

I've seen it quoted as "up to 30 dB". That's probably under ideal
(or ideally-bad) conditions, though.

e.g., for a rubber-duckie scanner antenna ?

There's an additional penalty of 20 dB imposed on
any antenna that has the word "duckie" in its name.
;-) ;-) ;-)

Heh. Yeah. Last weekend, my partner-in-repeater-crime and I ran some
simple outdoor-range tests on a few 2-meter beams, using an HP signal
generator and HP spectrum analyzer. We used a quarter-wave whip,
mag-mounted on a sheet of steel, as the reference antenna.

A two-element HB9CV beam was around 8 dB better than the reference
antenna, with a front-to-back ratio of 6-8 dB.

An Elk log-periodic 6-element beam measured out as quite similar to
the HB9CV (but has a lower SWR across the band) - 8 dB up, and about 7
dB front-to-back.

A 3-element Yagi made out of PVC and steel measuring tape segments,
designed for foxhunting, was 9-10 dB up and had about a 20 dB
front-to-back ratio at its deepest null.

Rubber duckies? Ugh. A Yaesu helically-wound duck was around 10 dB
worse than the reference antenna. An RD-9 "high gain" base-loaded
2-meter/440 superflexible antenna was around 12 dB worse than the
reference antenna.

I'd always heard that rubber duckies were actually rubber dummy loads.
Now I've actually seen the results for myself. Yeech.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Homer J wrote:
Here is a reference to a technical look at short loop antennas from the
1950's by Wheeler.

H. A. Wheeler, "Fundamental Limitations of Small Antennas", Proc. IRE,
vol. 35, pp. 1479-1484


More specifically, the December 1947 issue

From a practical standpoint, this paper is quite useful, although it
mixes effects of the matching network in with the antenna, which the
more rigorous analyses don't. It also doesn't provide any backup for
its assertion of the validity of the "radiansphere" or "radianlength",
hence the equations might not be valid over all possible antennas.

Wheeler's 1975 paper ("Small Antennas", IEEE Trans Ant & Prop, V AP-23,
#4, July 1975, pp462-469) revisits some of the stuff in the earlier
paper and provides more backup and describes the limitations of the
"radian sphere" model (which he defines as the volume within which the
reactive power density is higher than the radiation power density).

Of particular interest to would-be miracle small antenna builders is
that he specifically mentions the problems if there is anything
conductive or magnetic within the empty space oustide the "antenna" but
within the radiansphere (defined as lambda/2pi). The latter paper also
discusses some electrically small antennas (for 15 kHz, lambda=20km)



This is can found in a technical library with access to the IEEE
publications web site (e.g. university or military tech library)


Thane-fer
Homer


"Dave Platt" wrote in message
...

d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?


The usual figure one sees bandied about is 20 dB.


I've seen it quoted as "up to 30 dB". That's probably under ideal
(or ideally-bad) conditions, though.


20 dB is probably representative of the "polarization purity" of a run
of the mill antenna in its preferred direction.

On Apr 7, 10:48 am, Jim Lux wrote:
Homer J wrote:
Here is a reference to a technical look at short loop antennas from the
1950's by Wheeler.

H. A. Wheeler, "Fundamental Limitations of Small Antennas", Proc. IRE,
vol. 35, pp. 1479-1484

More specifically, the December 1947 issue

From a practical standpoint, this paper is quite useful, although it
mixes effects of the matching network in with the antenna, which the
more rigorous analyses don't. It also doesn't provide any backup for
its assertion of the validity of the "radiansphere" or "radianlength",
hence the equations might not be valid over all possible antennas.

Wheeler's 1975 paper ("Small Antennas", IEEE Trans Ant & Prop, V AP-23,
#4, July 1975, pp462-469) revisits some of the stuff in the earlier
paper and provides more backup and describes the limitations of the
"radian sphere" model (which he defines as the volume within which the
reactive power density is higher than the radiation power density).

Of particular interest to would-be miracle small antenna builders is
that he specifically mentions the problems if there is anything
conductive or magnetic within the empty space oustide the "antenna" but
within the radiansphere (defined as lambda/2pi). The latter paper also
discusses some electrically small antennas (for 15 kHz, lambda=20km)



This is can found in a technical library with access to the IEEE
publications web site (e.g. university or military tech library)

Thane-fer
Homer

"Dave Platt" wrote in message
...

d. If a receiving signal is well polarized in
one direction, say vertically, how much loss
would one expect if the receiving antenna is
oriented such that its preferred polarization is
horiz. ?

The usual figure one sees bandied about is 20 dB.

I've seen it quoted as "up to 30 dB". That's probably under ideal
(or ideally-bad) conditions, though.

20 dB is probably representative of the "polarization purity" of a run
of the mill antenna in its preferred direction.

To be more specific is Wheeler refering to small FULL wave
antennas or smal fractional wave antennas.?
These are very different and one must be absolutely clear with
what Wheeler is dealing with.
My guess is that he is refering to fractional wave antennas
which is very common in the communication field
Regards
Art Unwin KB9mx xg (uk)

On Mon, 7 Apr 2008 09:09:04 -0700 (PDT), Art Unwin
wrote:

To be more specific is Wheeler refering to small FULL wave
antennas or smal fractional wave antennas.?
These are very different and one must be absolutely clear with
what Wheeler is dealing with.
My guess is that he is refering to fractional wave antennas
which is very common in the communication field

hi Arthru,

But even more meaningful, are you speaking of large FRACTIONAL wave
antennas, or small WAVE full antennas? My guess is probably both
which is common in your communication.

73's
Richard Clark, KB7QHC

On Apr 7, 12:19 pm, Richard Clark wrote:
On Mon, 7 Apr 2008 09:09:04 -0700 (PDT), Art Unwin

wrote:
To be more specific is Wheeler refering to small FULL wave
antennas or smal fractional wave antennas.?
These are very different and one must be absolutely clear with
what Wheeler is dealing with.
My guess is that he is refering to fractional wave antennas
which is very common in the communication field

hi Arthru,

But even more meaningful, are you speaking of large FRACTIONAL wave
antennas, or small WAVE full antennas? My guess is probably both
which is common in your communication.

73's
Richard Clark, KB7QHC

Wheeler is known for his work on small electricaly or fractional
wavelength antennas.
I was enquiring if the referred paper on limits were of small
electrical or fractional
wavelength antennas or has he broardened out to include small full
wave antennas.
Big difference

Art Unwin wrote:
On Apr 7, 10:48 am, Jim Lux wrote:

Homer J wrote:

Here is a reference to a technical look at short loop antennas from the
1950's by Wheeler.

H. A. Wheeler, "Fundamental Limitations of Small Antennas", Proc. IRE,
vol. 35, pp. 1479-1484

More specifically, the December 1947 issue

From a practical standpoint, this paper is quite useful, although it
mixes effects of the matching network in with the antenna, which the
more rigorous analyses don't. It also doesn't provide any backup for
its assertion of the validity of the "radiansphere" or "radianlength",
hence the equations might not be valid over all possible antennas.

Wheeler's 1975 paper ("Small Antennas", IEEE Trans Ant & Prop, V AP-23,
#4, July 1975, pp462-469) revisits some of the stuff in the earlier
paper and provides more backup and describes the limitations of the
"radian sphere" model (which he defines as the volume within which the
reactive power density is higher than the radiation power density).

Of particular interest to would-be miracle small antenna builders is
that he specifically mentions the problems if there is anything
conductive or magnetic within the empty space oustide the "antenna" but
within the radiansphere (defined as lambda/2pi). The latter paper also
discusses some electrically small antennas (for 15 kHz, lambda=20km)



To be more specific is Wheeler refering to small FULL wave
antennas or smal fractional wave antennas.?

Any size antennas... Wheeler's analysis essentially points out that when
talking about "size" of an antenna, it's not just the mechanical
dimensions of the metal that counts. You also have to account for stored
energy in the fields around the antenna.

here's the abstract from the 1947 paper:
"A capacitor of inductor operating as a small antenna is theoretcially
capable of intercepting a certain amount of power, independent of its
size, on the assumption of tuning without circuit loss. The practical
efficiency relative to this ideal is limited by the "radiation power
factor" of the antenna as compared with the power factor and bandwidth
of the antenna tuning. The radiation power factor of either kind of
antenna is somewhat greater than
1/(6*pi)* A*b/L^2
in which Ab is the cylindrical volume occupied by the antenna, and L is
the radianlength (defined as 1/(2*pi) wavelength) at the operating
frequency. The efficiency is further limited by the closeness of
coupling of the antenna with its tuner. Other simple formulas are given
for the more fundamental properties of small antnenas and their behavior
in a simple circuit. Examples for 1-Mc. operation in typical circuits
indicate a loss of aboute 35 db for the I.R.E. standard capacitive
antenna, 43 db for a large loop occupying a volume of 1 meter square by
0.5 meter axial length, and 64 db for a loop of 1/5 these dimensions.
"
(forgive the typos when I copied it)



I would suggest that nobody attempt to argue the applicability or not of
this paper from just the abstract. Get the paper, and the one from 1975
(and the ones by the other authors he cites: Chu, Fano, Wait, etc.).
The maturity of the analysis of this sort of problem has advanced
significantly over the last 60 years.

Wow,

Cannot believe Wheeler has such a following, what he was dealing with at the
time was low frequency loop antennas for navigation (e.g. LORAN, aircraft
Omni stations) down around 300 to 500 KHz. If I remember correctly he made a
statement in his paper that antenna was less than 1/6 of a wavelength in
length.

I was interested because my design requirements for our customer was for a
fairly wide bandwidth but with a shorten radiator rod to be canceled in a
ordinary looking plastic housing for aesthetic reasons.

Homer J.



"Jim Lux" wrote in message
...
Art Unwin wrote:
On Apr 7, 10:48 am, Jim Lux wrote:

Homer J wrote:

Here is a reference to a technical look at short loop antennas from the
1950's by Wheeler.

H. A. Wheeler, "Fundamental Limitations of Small Antennas", Proc. IRE,
vol. 35, pp. 1479-1484

More specifically, the December 1947 issue

From a practical standpoint, this paper is quite useful, although it
mixes effects of the matching network in with the antenna, which the
more rigorous analyses don't. It also doesn't provide any backup for
its assertion of the validity of the "radiansphere" or "radianlength",
hence the equations might not be valid over all possible antennas.

Wheeler's 1975 paper ("Small Antennas", IEEE Trans Ant & Prop, V AP-23,
#4, July 1975, pp462-469) revisits some of the stuff in the earlier
paper and provides more backup and describes the limitations of the
"radian sphere" model (which he defines as the volume within which the
reactive power density is higher than the radiation power density).

Of particular interest to would-be miracle small antenna builders is
that he specifically mentions the problems if there is anything
conductive or magnetic within the empty space oustide the "antenna" but
within the radiansphere (defined as lambda/2pi). The latter paper also
discusses some electrically small antennas (for 15 kHz, lambda=20km)



To be more specific is Wheeler refering to small FULL wave
antennas or smal fractional wave antennas.?

Any size antennas... Wheeler's analysis essentially points out that when
talking about "size" of an antenna, it's not just the mechanical
dimensions of the metal that counts. You also have to account for stored
energy in the fields around the antenna.

here's the abstract from the 1947 paper:
"A capacitor of inductor operating as a small antenna is theoretcially
capable of intercepting a certain amount of power, independent of its
size, on the assumption of tuning without circuit loss. The practical
efficiency relative to this ideal is limited by the "radiation power
factor" of the antenna as compared with the power factor and bandwidth of
the antenna tuning. The radiation power factor of either kind of antenna
is somewhat greater than
1/(6*pi)* A*b/L^2
in which Ab is the cylindrical volume occupied by the antenna, and L is
the radianlength (defined as 1/(2*pi) wavelength) at the operating
frequency. The efficiency is further limited by the closeness of coupling
of the antenna with its tuner. Other simple formulas are given for the
more fundamental properties of small antnenas and their behavior in a
simple circuit. Examples for 1-Mc. operation in typical circuits indicate
a loss of aboute 35 db for the I.R.E. standard capacitive antenna, 43 db
for a large loop occupying a volume of 1 meter square by 0.5 meter axial
length, and 64 db for a loop of 1/5 these dimensions.
"
(forgive the typos when I copied it)



I would suggest that nobody attempt to argue the applicability or not of
this paper from just the abstract. Get the paper, and the one from 1975
(and the ones by the other authors he cites: Chu, Fano, Wait, etc.). The
maturity of the analysis of this sort of problem has advanced
significantly over the last 60 years.

In message , "Jim, K7JEB"
writes

Land mobile and aircraft radios almost invariably
use vertically polarized antennas. That wave
polarization is generally maintained under conditions
of reflection and refraction over short- and long-
distance paths. For polarization rotation to occur
during propagation, the medium generally must be
birefringent (eg: the ionosphere). This rarely occurs
with terrestrial waves.

The local 2m beacon ( about 80 miles north and shielded by a local hill
) here is horizontally polarised. However if I beam south it is much
stronger on vertical polarisation. I have no idea why.

Brian GM4DIJ
--
Brian Howie