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 <[email protected]> wrote: From: Ken Alexander <[email protected]> Subject: Re: [Elecraft] Education please To: "Elecraft Reflector" <[email protected]>, "Lee Buller" <[email protected]> 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 <[email protected]> wrote: From: Lee Buller <[email protected]> Subject: [Elecraft] Education please To: "Elecraft Reflector" <[email protected]> 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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
