[TowerTalk] Shunt Feeding, Can this be?
n4zr at contesting.com
Wed Nov 16 07:03:27 EST 2005
Count me as another dissenter. My 97 feet of Rohn 25G has stacked tribanders at 97 and 69 feet, a shorty 40 at 104, and a 4-element 80m dipole array hung off it, with the feedlines coming in to the tower at about 30 feet above ground. The guy wires are insulated from the tower, and the top set is Phillystran. The middle set have 21-foot power pole insulators at their inner end, and the bottom set are insulated with a single jonny-ball about 3 feet from the tower.
I had zero luck feeding this critter with a classic shunt feed - series cap only. Then I tried an omega match, and was able to get a 1:1 match at 1830 within minutes. Whatever impedance the 50-foot tap point represents, the omega was able to match it. I suppose if it is quite low then efficiency is probably impaired, but it does seem to work - 75 countries on 160 to date, and WAC.
73, Pete N4ZR
At 05:57 PM 11/15/2005, ersmar at comcast.net wrote:
> Sorry - but shunt feeding doesn't work in your part of Texas.
> I'm just kidding. But if your 45G means Rohn 45G tower, I'm assuming then that your tower is properly guyed. If so, then I believe your first step would have to be to insulate the tower from all your guy wires by replacing them with Phillystran or similar, or installing multiple porcelain insulators in each guy wire. And a bunch of other steps that I'm not familiar with.
> My tower, and all others that I know to be shunt-fed, are self-supporting, unguyed structures. All the shunt-feeding tricks I've learned here on TowerTalk apply to that type of support.
> Perhaps others around here have been able to shunt-feed their guyed towers and will jump in. Or maybe you would be able to install an inverted L or some other wire antenna off your tower.
> How about a little bit more info on your tower?
>Gene Smar AD3F
>> OK, with all this talk about shunt feeding - maybe I am ready to take the
>> plunge. I am usually not so stupid but I have read about shunt feeding and
>> end up with more questions than answers.
>> My tower is a 45G with an Optibeam OB17-4 on top (40 foot boom - 17
>> elements) and then a WARC-7 (7 elements on a 14 foot boom) about 12 feet
>> about the Optibeam. So, quite a bit of top loading and with 80 foot tower I
>> have wondered about shunt feeding for 80 and esp 160 meters.
>> Can someone point me to a good step by step resource and will you also
>> answer my questions afterwards? I would love to do better on 160 meters.
>> I am about 70 miles north of Dallas, Texas.
>> Gary, N5PHT
>> -----Original Message-----
>> From: towertalk-bounces at contesting.com
>> [mailto:towertalk-bounces at contesting.com] On Behalf Of donhall161
>> Sent: Tuesday, November 15, 2005 4:04 PM
>> To: ersmar at comcast.net; Pat Chiles; towertalk at contesting.com
>> Subject: Re: [TowerTalk] Shunt Feeding, Can this be?
>> My shunt fed tower had similar BW. Worked like a charm (over 190 countries
>> from two locations in Texas). Like Gene, I don't ask, just enjoy.
>> 73 Don K5AQ
>> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>> questions and ask for Sherman, W2FLA.
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>TowerTalk mailing list
>TowerTalk at contesting.com
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