[K3] CP antenna article in Dec QST

[Edward R Cole]

My 144-MHz dual-polarity diversity receiver is exactly what you
describe, only for HF in your case:  two orthogonal antennas, each
fed to one of the K3 receivers.  In my case a dual-channel 144-MHz Rx
converter is feeding 28-MHz to the K3 and fed by my X-yagis.  To
observe the polarity effects the two separate receiver audio streams
are fed to a a computer which runs Linrad, a program for weak-signal
reception that also resolves the polarity angle from the two
orthogonal signals.

http://www.kl7uw.com/eme144.htm
http://g7rau.demon.co.uk/sm5bsz/index.htm

No fancy coax network is needed; just make the baluns and feedlines identical.

73, Ed
BTW Eric is a member of the ARRL 600m Experimental Group: WD2XSH.

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Message: 8
Date: Fri, 12 Nov 2010 19:31:56 -0000
From: "Bill VanAlstyne W5WVO" <[hidden email]>
Subject: Re: [Elecraft] [K3] CP antenna article in Dec QST [was:
         Education       please]
To: "Elecraft Reflector" <[hidden email]>
Message-ID: <6720A8423C184619A1BE732734B53E3C@BILLHP9250>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
         reply-type=original

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




73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-800*w, 432-100w, 1296-testing*, 3400-winter?
DUBUS Magazine USA Rep [hidden email]
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