Posted by
Bill VanAlstyne W5WVO on
Nov 12, 2010; 7:31pm
URL: http://elecraft.85.s1.nabble.com/Education-please-tp5732495p5733715.html
Just as a heads-up for anyone interested in this subject -- in the December
QST just now arriving in subscribers' hands, there is a cool article on X-O
circular polarization (CP) antennas. The author (Eric Nichols, KL7AJ)
discusses the fact that all F-layer ionospheric propagation is actually
circular and arrives at the receiving antenna by way of one of two different
refraction paths, depending on... well, you can read the article for the
theoretical details. He says all of this has actually been well understood
in physics and radio engineering circles since the 1930s, but (with a few
exceptions) has had scant mention in the ham radio literature.
The executive summary is that you can build a receive antenna (which
empirically demonstrates and proves the theory) consisting of two inverted
vee antennas constructed around a central support, with the four legs
arranged accurately such that the slopes of the legs are all identical, the
angles between the legs are all 90 degrees, and the two feedlines (connected
through identical baluns) are precisely the same length. By then inserting a
1/4-wavelength (90 degree) delay line in one dipole's feedline and then
adding the signals together through a T or some more sophisticated combiner,
you will get either a large increase in signal strength with respect to
either dipole individually, OR a commensurately large loss of signal
strength with respect to either dipole individually -- depending on which
variety of circular polarization (X-wave or O-wave) you are getting from the
station being received at the moment.
This is one kind of orthogonal receiving antenna that could have very
practical uses on the HF bands, especially if you have a diversity-capable
receiver such as the K3.
One possibility I can think of: You could set up two separate X-O inverted
vee antenna systems on two separated support masts, each magnetically
aligned as described in the article, with one antenna set up for X waves and
the other set up for O waves. Connect the X-wave configured antenna to one
receiver, the O-wave configured antenna to the other receiver. And say
goodbye to a lot of the QSB normally associated with F-layer-propagated
reception! (At least it seems to me that it would have that effect.)
Another possibility: use ultra-fast PIN diode switching of the 90-degree
delay line and reconstruct both an X and O output from a single antenna.
Since even PIN diodes probably can't switch faster than, say, one cycle at
14 MHz (about 72 nanoseconds), I don't know if this would work, as you would
be switching multiple cycles and fractions of cycles (asynchronously) back
and forth... Would this matter? You would end up with a 3-dB loss on each
leg, but that in itself should be trivial; absolute sensitivity is not an
issue at HF. But would the chopped-up waves be properly demodulated in the
receivers?
This is about where the engineering of it goes over my head... Comments?
Bill W5WVO
-----Original Message-----
From: Ken Alexander
Sent: Friday, November 12, 2010 15:16
To: Elecraft Reflector ; Lee Buller
Subject: Re: [Elecraft] Education please
OK, I guess the ham application for an orthogonal antenna would be to use
two loops at 90 degrees to each other. With the electronic trickery I
mentioned below you would have yourself a dandy direction finding antenna.
Great for transmitter hunts and tracking down jammers and other bad guys.
73 - Ken
--- On Fri, 11/12/10, Ken Alexander <
[hidden email]> wrote:
From: Ken Alexander <
[hidden email]>
Subject: Re: [Elecraft] Education please
To: "Elecraft Reflector" <
[hidden email]>, "Lee Buller"
<
[hidden email]>
Date: Friday, November 12, 2010, 10:04 AM
This is subject to much correction from people who are smarter than me, but
my oversimplified description is that an orthogonal antenna basically
consists of three loop antennas oriented in three planes that are at right
angles to each other (X, Y and Z axes if you remember your basic geometry).
The antenna are bidirectional in each of those planes.
With some associated electronic wizardry, you can compare the signals
received by each antenna and establish the direction (in three-dimensional
space) of a given transmitter. Sort of a method of electronic
triangulation.
I don't know how much application it has in ham radio. I don't recall
seeing any ham call signs associated with the documents I read during my
Google search! It looks like most of the uses are industrial.
Hope that gets you started, and like I said, probably subject to some
clarification by brainier people.
73,
Ken Alexander
VE3HLS
--- On Fri, 11/12/10, Lee Buller <
[hidden email]> wrote:
From: Lee Buller <
[hidden email]>
Subject: [Elecraft] Education please
To: "Elecraft Reflector" <
[hidden email]>
Date: Friday, November 12, 2010, 9:32 AM
What the heck is a orthogonal antenna? Would someone define it or give an
example? I have Googled it but it is all mumbo-jumbo to me.
Lee Buller
K0WA
Still learning after all these years!
In our day and age it seems that Common Sense is in short supply. If you
don't
have any Common Sense - get some Common Sense and use it. If you can't find
any
Common Sense, ask for help from somebody who has some Common Sense. Is
Common
Sense divine?
Common Sense is the image of the Creator expressing revealed truth in my
mind.
- J. Wolf
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