[TowerTalk] OT - Tri-band Coupled Resonator Antenna Design

[Gene Smar]

Rick:

     I bought my GP-15 in 2001 and installed it at the top of the tower's
mast at 80 feet.  Before I mounted it I adjusted the length of one of the
radials for best SWR at, IIRC, 52.0 MHz.  Spec sheet
http://www.cometantenna.com/wp-content/uploads/2013/09/GP-15-manual-rev-6-13
.pdf    says the 2:1 SWR bandwidth is about 1 MHz and that minimum SWR can
be adjusted anywhere in the 6M band.    

     When I wrote "it worked great" I meant I was able to access the MARS 2M
packet repeater in Harrington, DE with 20W, a distance of about 140 miles
from my QTH.  Local repeaters were a no-brainer.  Coax run was/is 135 feet
of RG-213.


73 de
Gene Smar  AD3F



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
Richard (Rick) Karlquist
Sent: Friday, June 02, 2017 8:06 PM
To: ersmar <ersmar at verizon.net>; Clay Autery <cautery at montac.com>;
towertalk at contesting.com
Subject: Re: [TowerTalk] OT - Tri-band Coupled Resonator Antenna Design

On 6/2/2017 1:12 PM, ersmar wrote:
> Clay:
> 
>       Unless you're deadset against store bought, check out Comet
Antenna's GP-15. It'll cover 6, 2 and 3/4M in one vertical stick. I have one
at 80 ft AGL and it works great.
> 
> 73 de
> Gene Smar AD3F

I wasted money on this antenna and then found that:

1.  It comes tuned to 52 MHz at the factory 2.  The SWR at 50.1 MHz is quite
high 3.  It CANNOT be retuned to 50.1 MHz per the manufacturer.
4.  Physics prevents retuning it without screwing up the other two bands.

You say your antenna "works great".  Does it work great on 50.1 MHz?  Or
just 52 MHz?  I know mine worked great on 52 MHz, but not 50.1 MHz.

Rick N6RK


> 
> -------- Original message --------
> From: Clay Autery <cautery at montac.com>
> Date: 06/02/2017  3:00 PM  (GMT-05:00)
> To: towertalk at contesting.com
> Subject: [TowerTalk] OT - Tri-band Coupled Resonator Antenna Design
>   
> Anyone have any experience designing C-R antennae.
> 
> I'm building a tri-band dipole for 6m, 2m, 70cm that will be oriented 
> vertically and hung off one of my loop masts on a non-conductive arm.
> 
> 6m driven element in the center.  2 x 2m dipole 180 degrees from each 
> other "d" distance form 6m.  Same with UHF, 2 x 70 cm dipole 180 
> degrees from each other and 90 degrees offset from 2m...  All dipole 
> centers on the same perpendicular plane.  Parasitic dipoles connected 
> with insulating plates, one on each end.
> Choke at the feed point and another at 1/4 lamda from the feed-point 
> to try and help keep the feed-line from interacting with the antenna 
> since it's not practical to keep it perpendicular for a sufficient
distance.
> 
> Using EZNEC 6+ and the equations in the Antenna Book to set the 
> separation distances from the driven element and get a good starting 
> position for lengths vs. element diameter, etc.
> 
> Was just thinking it might be nice to talk to someone who has built 
> something similar before.
> 
> Want to use it vertically oriented as a sort of omni for use on the 
> repeaters in my local area (yep, we have a local 6m repeater).  Don't 
> need a beam.
> Secondarily, it is an academic/skills exercise for later projects to 
> build multi-band HF ants using the same basic concept(s).
> 
> Know this is a little OT for Tower Talk, but the Antenna reflector has 
> zero traffic.
> 
> 73,
> 
_______________________________________________



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