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

Jim Brown jim at audiosystemsgroup.com
Sat Jun 3 12:46:28 EDT 2017


Several thoughts. First, the fact that it's tuned to 52 MHz with a 2:1 
SWR bandwidth of 1 MHz and that it's vertically polarized tells me that 
it's designed for FM repeater operation. Nothing wrong with that, but it 
wouldn't be my first choice to work CW, SSB, and digital modes.  Also 
nothing wrong with omnis -- while in Chicago, I had a lot of fun with 
pairs of stacked PAR loops for 6, 2, and 440, and worked a lot of grids 
on 6M. I worked a lot of grids that were in the opposite direction from 
where I would have pointed a beam if I had one (and I later did). I also 
worked AU on both 6 and 2.

As to "works good" -- the path from Gene's QTH to Harrington, DE goes 
over mostly flat land and a lot of water. Could it be that tropo has a 
lot to do with working that repeater?

73, Jim K9YC

On Sat,6/3/2017 12:47 AM, Gene Smar wrote:
> 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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