View Full Version : Gimme an X, gimme an O
kl7aj
12-14-2005, 04:39 PM
I don't know how many are aware of this but any HF signal that propagates through the ionosphere becomes circularly polarized. Actually there are two circularly polarized modes in any magnetized plasma, the X mode and the O mode. Each of these waves can take considerably different paths, especially in high latitude regions. Oddly enough, even though the X and O modes have been known since the very first ionosondes, (and are always displayed individually on any modern ionograms) the ARRL literature is entirely void of any mention of X and O modes. This is very strange. Under nearly every case of ionospheric propagation, you can realize a 6 db gain in signal strength by using circularly polarized antennas....not only that, but you can actually REUSE hf frequencies by judicious use of CPOL. I'd like to see more of this on amateur radio discussions...this is nothing new..any ionospheric scientist or COMMERCIAL user knows all about X and O propagation. Why the conspiracy of silence among us supposedly scientific hobbyists?
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Eric
KA4DPO
12-14-2005, 04:55 PM
The phenomenon is known as Farraday Rotation..
kl7aj
12-14-2005, 05:00 PM
Quote[/b] (KA4DPO @ Dec. 14 2005,09:55)]The phenomenon is known as Farraday Rotation..
Nope, this is a different phenomenon, although often with similar looking results to Faraday rotation. You don't get the two different azimuth paths with Faraday rotation. Additionally the X and O divergence is GREATER with frequency, unlike Faraday rotation which decreases with frequency.
Both very interesting and useful properties though!
eric
KI4LZK
12-14-2005, 05:09 PM
I am going to have to read up on this, sound very interesting. You wouldn't happen to know any good sources about how HF travels in Space would you?
kl7aj
12-14-2005, 05:32 PM
Quote[/b] (ki4lzk @ Dec. 14 2005,10:09)]I am going to have to read up on this, sound very interesting. #You wouldn't happen to know any good sources about how HF travels in Space would you?
The most definitive work is "Radio waves in the Ionosphere" by K.G. Budden, Cambridge Press. It might be a bit hard to get a hold of if you aren't associated with a physics lab. The most accessible information is probably the Lowell Digisonde site. (ULMCAR) The Lowell University digisonde is the world standard of ionospheric sounders, and they have a lot of good information.
eric
KI4LZK
12-14-2005, 05:40 PM
I will have to check them out.
kl7aj
12-14-2005, 06:05 PM
Quote[/b] (ki4lzk @ Dec. 14 2005,10:40)]I will have to check them out.
Ionospheric intro (http://image.gsfc.nasa.gov/publication/document/2003_reinisch.doc)
http://image.gsfc.nasa.gov/publication/document/2003_reinisch.doc
Here's a good introduction to X and O modes, as well as ionosondes.
eric
So could you tell me how to make one of those XO dipoles? Do I have to solder? I want it for channel 19 please. I'm gonna shoot circle-skip.
kl7aj
12-14-2005, 06:46 PM
Quote[/b] (AK7V @ Dec. 14 2005,11:30)]So could you tell me how to make one of those XO dipoles? #Do I have to solder? #I want it for channel 19 please. #I'm gonna shoot circle-skip.
you can use wire nuts
wa9cwx
12-15-2005, 08:39 PM
Did someone say wire nuts ?
ouch
I use XOXOXOXO on the bottom of my Xmas cards and they travel around the world. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif