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Cycloid dipole, circular polarization antenna for dense foliage, mountainous terrain

antenna gmrs foliage elevation omnidirctional home built

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#1 YourGMRS



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Posted 11 July 2019 - 06:32 PM

We have a 40w Motorola repeater and I've got an ANLI-100 antenna about 15' over the house, connected with 50' of LMR400 cable.  It's on a metal roof, the house is at about 3000' ASL.  In the immediate valley, pretty much with 'line of sight' - but with dense foliage, they're around 2200'.  I haven't measured SWR, do not have a SWR meter, but I think it should be close enough to work even considering the line loss and slightly out-of-band from ham dual band VHF/UHF antenna.  When I first got repeater, in the winter time, without leaves on most trees, It worked well and as expected.  I could go about 4-5 miles away... Now, in the summer, with very dense foliage, I can hardly make it a few hundred feet away!  There is both a very steep elevation change, as this location is in mountainous area, and very very dense foliage.  


In my research, it seems that a "circular polarized omnidirectional" antenna has been tested and used successfully by Motorola - a long time ago - with use in UHF frequencies.  


I'm looking to see if anyone has experience building an antenna like one of these "cycloid dipole" antennas for the GMRS frequencies?





Anyone have helpful thoughts on if this would improve reception for me, in the foliage?

#2 Jones


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Posted 12 July 2019 - 09:05 AM

Circular polarization does work to make RF cut through difficult areas. I have not seen any commercially made circularly polarized antennas for UHF, but I can say that almost EVERY radio station on the VHF broadcast band (FM 88-108MHz) uses a cycloid, or other type of circularly polarized antenna system.  The science is well proven for transmitting.  The question would be: Can they receive as well?





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#3 Ian


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Posted 12 July 2019 - 09:39 AM

A buddy of mine flies drones.  Be careful, left- and right-handed polarization are not the same!


Edit:  Yes, he learned that the crash way.

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