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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?

 

https://ka7oei.blogs...irectional.html

http://www.wa7x.com/cycloid_info.html

 

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?

 

https://www.eriinc.c...zed-fm-antenna/

 

http://www.progressi...enna_PT729.html


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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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Also tagged with one or more of these keywords: antenna, gmrs, foliage, elevation, omnidirctional, home built

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