Incoming radio wave polarisation
 

On Mar 16, 2:48 pm, (Richard Harrison)
wrote:
Art wrote:

"Normal mode helicals are commonly used on HF."

Yes. Such antennas include small diameter coils making up solenoids. The
turns act as small stacked loops.

A small loop acts as a short dipole but with its E and H fields
interchanged. See page 58 of the 3rd edition of "Antennas" by Kraus,
Marthefka, et al.

Best regards, Richard Harrison, KB5WZI

I did not say that. The quote is from somewhere else.
I am sure that he will be happy about the facts that you
have revealed to him as a personal favor and a book
that he can read up for himself what "Normal mode" means
Then explain it to you so you understand what you read
In the mean time I will try loading up a solenoid on 20 M
to see how many people are using them..

Incoming radio wave polarisation
 

Art wrote:
"I have an on order a tilting system for my antenna to probe the
polarisation of incoming signals for maximum audio clarity and gain."

That may be interesting but do you ever recall cross polarization of an
incoming ionosphere reflected signal being unreadable because
polarization was wrong?

So many different and quickly changing path variations exist in the
ionosphere that the best antenna to use is based on probability.

E.A. Laporte says on page 215 of "Radio Antenna Engineering":

"To make best use of this effect (randomness of ionospheric waves) it is
desirable to employ complimentary antennas for transmitting and
receiving."

Most commercial HF circuits I`ve experienced and seen use horizontal
polarization. It is because much severe man made interference arriving
at a receiving antenna is vertically polarized.

Best regards, Richard Harrison, KB5WZI

Incoming radio wave polarisation
 

I apologize to Art Unwin. It was Owen Duffy who wrote:
"Normal mode helicals are commonly used on HF."

A normal mode helical antenna radiates perpendicularly to the axis of
the helix. The axial mode helix antenna invented by John Kraus radiates
in the direction of the axis of the helix.

Best regards, Richard Harrison, KB5WZI

Incoming radio wave polarisation
 

"Owen Duffy" wrote in message
...
"AI4QJ" wrote in
:

...
Are you talking about the possibility of Art communicating with other
people who are transmitting on similar helical circularly polarized
antennas where CW vs CCW direction must be considered? I dismissed

If this is his compact wonder, it is probably not an axial mode helical.
(I don't know that one could ever describe an axial mode helical as
'compact'.)

Normal mode helicals deliver linear polarisation.

this possibility entirely. Most hams's signals arrive either veritcal,
norizontal or somewhere in between (not rotating) originating at a
linear polarized source. Is he communicating with satellites? I really
haven't heard of helix antennas on the HF bands other than the Unwin
compact model. If so, then yes, you can only switch the feedpoint to

Normal mode helicals are commonly used on HF.

change from CW to CCW and that can make a BIG difference in gain. The
probability of Art finding another HF helical to QSO with should be
negligible to null. Satellites are another matter.

Owen

Hi Owen

I have no disagreement with your thoughts. I do want to point out that
the short helical antenna named Quad Helix does give good CP normal to the
helix axis.

Jerry KD6JDJ

Incoming radio wave polarisation
 

Art wrote:
"Anybody out there follow such a procedure with the antenna or use a
homebrew or commercial instrument to save time?"

Search on goniometer.

I was doing my thing in Argentina when El Jefe or the boss called me
into his office to ask me why my assistant had requisitioned a
goniometer instead of the company doctor. I had to explain that it was
not a medical diagnostic instrument.

Best regards, Richard Harrison, KB5WZI

Incoming radio wave polarisation
 

My apology to Edmund A. Laport, author of a marvelous book: "Radio
Antenna Engineering". He does not add an "e" after the "t" in his name.
I was the culprit that did it in an earlier post.

Best regards, Richard Harrison, KB5WZI

Incoming radio wave polarisation
 

"Jerry" wrote in
news:dniDj.714$Nr1.510@trnddc01:

....
Hi Owen

I have no disagreement with your thoughts. I do want to point out
that
the short helical antenna named Quad Helix does give good CP normal to
the helix axis.

Hi Jerry,

John Kraus' explanation of "normal mode" is where the radiation normal to
the helix axis dominates. On that basis, the Quad Helix (which he
discusses in his book) is neither an axial mode helix nor a normal mode
helix, it is large enough that it has significant radiation both normal
and axial, but not large enough to be dominated by the axial lobe, and it
is a multi-filar helix which allows CP normal to the helix axis.

The Quadrifilar Helix is an interesting antenna, and I was aware of your
particular interest from previous reading.

I don't know of a mono-filar normal mode helix that gives CP, but I
expect that two of them with phased feeds could be used in the same way
as crossed dipoles.

We are of course all guessing what Art had in mind, there is a conspicous
and familiar lack of coherent detail.

Owen

Incoming radio wave polarisation
 

"Owen Duffy" wrote in message
...
"Jerry" wrote in
news:dniDj.714$Nr1.510@trnddc01:

...
Hi Owen

I have no disagreement with your thoughts. I do want to point out
that
the short helical antenna named Quad Helix does give good CP normal to
the helix axis.

Hi Jerry,

John Kraus' explanation of "normal mode" is where the radiation normal to
the helix axis dominates. On that basis, the Quad Helix (which he
discusses in his book) is neither an axial mode helix nor a normal mode
helix, it is large enough that it has significant radiation both normal
and axial, but not large enough to be dominated by the axial lobe, and it
is a multi-filar helix which allows CP normal to the helix axis.

The Quadrifilar Helix is an interesting antenna, and I was aware of your
particular interest from previous reading.

I don't know of a mono-filar normal mode helix that gives CP, but I
expect that two of them with phased feeds could be used in the same way
as crossed dipoles.

We are of course all guessing what Art had in mind, there is a conspicous
and familiar lack of coherent detail.

Owen

Hi Owen

Art who??

Again, I am in full agreement with you on the limited application of nthe
term "Normal" to the radiation of a helix. In addition, I suspect there is
little need to elaborate, but, if a person had need, he could make a
bi-directional CP radiator from 1/2 of a Quad helix.

Jerry KD6JDJ

Incoming radio wave polarisation
 

Art Unwin wrote:
I have on order a tilting system for my antenna to probe the
polarisation of incoming signals
for maximum audio clarity and gain.
There are instruments out there that can automatically tell you the
polarisation
without one taking the trouble to pan the antenna in different
directions.
Anybody out there follow such a procedure with the antenna or use a
homebrew
or commercial instrument to save time?
Regards
Art
There's lots of ways to do this. calibration is always an issue.

For instance, two helices wound with opposite senses can be run through
a variable combiner. (the helices can be on the same form, and are
coincident.

There'a variety of tripole antennas used for this sort of thing, too.

3 crossed short, resistively loaded dipoles or loops is also used.

A very clever scheme uses half loops sticking out of a conductive sphere
as a simultaneous E and H field probe. The electronics is all inside
the sphere, and you bring the data out on fiber optics.

Incoming radio wave polarisation
 

Richard Harrison wrote:
Art wrote:
"I have an on order a tilting system for my antenna to probe the
polarisation of incoming signals for maximum audio clarity and gain."

That may be interesting but do you ever recall cross polarization of an
incoming ionosphere reflected signal being unreadable because
polarization was wrong?

So many different and quickly changing path variations exist in the
ionosphere that the best antenna to use is based on probability.

Or, use diversity combining. Several researchers in France have done
work with this, and discovered there's very little correlation between
the ordinary and extraordinary rays, so diversity combining is extremely
effective on HF skywave paths. They used physically co-located antennas
that had different polarization sensitivities (a loop and a whip, as I
recall).

E.A. Laporte says on page 215 of "Radio Antenna Engineering":

"To make best use of this effect (randomness of ionospheric waves) it is
desirable to employ complimentary antennas for transmitting and
receiving."



Most commercial HF circuits I`ve experienced and seen use horizontal
polarization. It is because much severe man made interference arriving
at a receiving antenna is vertically polarized.

Interference polarization is not necessarily the case. (I believe
there are measurements that show it is essentially random). More what
it is has to do with the antenna pattern of horizontal and vertical
antennas for sources at ground level and reasonably close. For example,
A horizontal antenna not too high over a ground plane has a null right
at zero elevation.


Best regards, Richard Harrison, KB5WZI