Polarization Questions
 

Hello,

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

b. Same question for a Scantenna ?

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 ?

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 olarization is horiz. ?

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

Thanks,
Bob

Polarization Questions
 

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

Polarization Questions
 

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!

From OP: Polarization Questions
 

Hi,

Thanks for replies.
Good info.

Regards,
Bob

--------------------
"Robert11" wrote in message
. ..
Hello,

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

b. Same question for a Scantenna ?

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 ?

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 olarization is horiz. ?

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

Thanks,
Bob

Polarization Questions
 

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!

Polarization Questions
 

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

Polarization Questions
 

Brian Howie, GM4DIJ, wrote:
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.

Nor do I, really. It could be that a close-by
piece of metal is oriented just-so to act as a
passive re-radiator for both horizontally and
vertically polarised waves (ie: it's at a
45-degree angle to both). It could be that your
beam actually has a relatively large, horizontally
polarised response in its back lobe. Or that
there is some interaction between the beam and its
(randomly polarised) feedline. Or that you live
in an anomalous neighborhood. ;-) ;-) ;-)

The sweepingly general statement I made about
radio waves not changing their polarity with
distance was made with the unstated assumption of
a propagation path relatively free of scattering
objects (re-radiators) and having a direct
line-of-sight path between transmitting and
receiving antennas.

Jim, K7JEB

Polarization Questions
 

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.

Polarization Questions
 

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)

Polarization Questions
 

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