+45 -45 Orthogonal Beams

[O.J. Lougheed]

Since I may have just stuck my foot in my mouth...

I have reasonably long boom beams for 2 meters and 432-438 MHz SSB. (The long Diamond yagis. I also have an assortment of short yagis for 2 and 440 FM. But we're not here to talk FM.) None up at the moment. Several years ago I discovered the Mt. Gardner repeater on Bowen Island. 63 miles (just over 100KM) north-northwest of me. My antennas are about 130 feet (40 meters) Above Mean Sea Level (AMSL). BUT! Turtleback Mountain on Orcas Island at 1536 ft. (468 m) is DIRECTLY in my path. (See attachment 1) But through the magic of diffraction (some do use the term refraction - let's not argue) the RF path to Gardner is a piece of cake!!! (And it's really not that far away. Attachment 2) When I first made contact I was using the (small Diamond) horizontally. I was thinking SSB contacts up the Strait. Turtleback is really only good for about 50 miles (80 m) at sea level -- I was really thinking of Mountain Top contacts with rovers (ie. Gabor) during contests on Vancouver Island or up the Sunshine Coast.

But I found Gardner as a signal source, and noticed that horizontal polarization was good! Years ago I read studies that showed polarization "twists" (I forget the term) with signal diffraction. But didn't try "orthogonal" - that is, plus or minus 45 degrees of the beam. The rule of thumb for cross polarization is 20 dB loss. I have found that one defraction is also about 20 dB loss. (They add up fast! I learned this when first licensed in Northern New Mexico and playing with reflection off Mesa faces as well as defraction into Santa Fe and Albuquerque over said Mesas. I was at Ghost Ranch.)

Long story short: Check this out: https://resources.system-analysis.cadence.com/blog/msa2021-using-dual-linear-polarization-antennas-in-mobile-communication

Experiment. Be good!

73, OJ, AD7DR

[Mark Spencer]

Hi OJ.  That is interesting.  Over the last 10 years or so I have increasingly formed an opinion that over the non optical paths I typically use on 144 thru 432 MHz the loss due to polarization mis match is considerably less than the theories would suggest.

I do wonder if perhaps some form of “twisting” is happening on non optical paths ?

I have never tried orthogonal polarization.  One day I might try circular polarization. 

At this point I am happy to take what I can get in terms of contacts.

73

Mark S

VE7AFZ