At most AM sites the tower(s) is (are) the radiator(s) and usually base fed, but sometimes a shunt feed arrangement is used. The base insulator is ceramic, with the best types filled with oil. Electrical for tower lighting is fed across the base insulator with a ring transformer where the primary and secondary are interlocked rings set at 90 degrees to one another for minimum capacitance, or a lighting choke which is a bifilar wound solenoid choke with bypass caps on each end. The center tap of the capacitors on the tower end is referenced (bonded) to the tower, on the line end the center tap is grounded. Chokes are typically used on lower impedance towers, since they're a hell of a lot cheaper than the transformers.
Bill ________________________________ From: "robertchar...@att.net" <robertchar...@att.net> To: Discussion of AM Radio in the Amateur Service <amradio@mailman.qth.net> Sent: Monday, January 12, 2009 2:36:00 PM Subject: Re: [AMRadio] 160 meter antenna Bill, I wasn't aware the broadcast towers were sitting atop of a insulator on the base...is this considered the norm? What type of material would you suppose the insulator is made with? -------------- Original message from BILL GUYGER <bguy...@sbcglobal.net>: -------------- This is a skirt type antenna it's a fairly common "trick" used at some AM b'cast sites. This way the tower can be grounded rather than sitting on a base > insulator. > > Bill AD5OL > > > > > ________________________________ > From: "robertchar...@att.net" To: w...@verizon.net; Discussion of AM Radio in > the Amateur Service > > Sent: Monday, January 12, 2009 12:13:42 PM > Subject: Re: [AMRadio] 160 meter antenna > > Hello Jack. I am familiar with the lynards that the climbers use as a safety > line while climbing the tower. Their are however 3 vertical lines made out of > what looks like guy wire with a circular ring near the base being fed by a > box > at the base. Just a FYI -------------- Original message from "JACK C. SHUTT" > : > -------------- > > > Hi Robert, > We have several of those wireless towers and monopoles around here, as well > Those side wires are safety cables that climbers can clip on to with > fall-arresting lanyards and harnesses, they are not radiators. > Anyway, the folded unipole is a worthwhile antenna to try. I have had > excellent > results with an inverted L running up the side of my 80' tower and the > "horizontal" portion sloping out to a tree. The "L' perhaps looks more like > a > vee with one short leg. Total length is about 135 ft. I use a coil and > capacitor parallel network at the base of the tower feeding the end of the > antenna wire then coax back to the shack. As always, a good radial system > really helps. > > 73, Jack, W9GT > > --- On Mon, 1/12/09, robertchar...@att.net wrote: > > From: robertchar...@att.net > Subject: Re: [AMRadio] 160 meter antenna > To: cozy...@yahoo.com, "Discussion of AM Radio in the Amateur Service" > > Date: Monday, January 12, 2009, 7:23 AM > > > Neal. Thanks for the link on building the Unipole. I had worked for Sprint > for > some time and I noticed they were using that same concept on many of their > towers. The link was exceptionally helpful > -------------- Original message from neal Newman : > -------------- > > > > Jim you only need 50 feet of verticle space. > > why not just build yourself a Folded Unipole antenna if you Dont know how. > Ask. its really easy. Just Run 3 lengths of #12 wire or if you have it #6 > wire. > short them up at around the 50 foot point and use 1" PVC > > Tubing as Insulators with clamps Down the side of the Tower. > > at the bottom Each wire is isolated with PVC from the Tower. > > BTW Each wire should be about 12" or more off the tower. then Tie all 3 > > wires > together with a ring of #12 and take that as the Lead to the antenna tuner. > Run > at Least 4 ground radials 50 feet long If you can get > > the space make them 120 feet... > > and you will have a Killer 160 antenna. if not make an inverted L Run a > > wire > thats 130 feet long. as far vertically as > > you can then run the rest out horizontally... again you need at least 4 > > ground > radials.... the unipole is what we use for > > Broadcast stations when we are tight for height or space on a grounded > > Tower. > > > > Neal-KA2CAF > > CE- WTTM/WHWH/WJDM/WIBG/WFYL > > > > > > --- On Sun, 1/11/09, Jim Miller WB5OXQ in Waco wrote: > > > > > From: Jim Miller WB5OXQ in Waco > > > Subject: [AMRadio] 160 meter antenna > > > To: "Discussion of AM Radio in the Amateur Service" > > > Date: Sunday, January 11, 2009, 11:28 PM > > > I always wanted to try am on 160 but like most do not have > > > enough room for a full size antenna, so, > > > I am considering building a 160 meter antenna at our > > > clubhouse because there is a 80' tower there and over an > > > acre of land to spread out a 1/2 wave dipole. Question is; > > > 1 Is a 1/2 wave wire dipole the best antenna for the band > > > considering there is room for it. > > > 2 Is 80' high enough for the center of the inverted V? > > > 3 How high do the ends need to be off of the ground? > > > 4 Should I feed it with coax or ladder line to the 10' > > > level (or other) then a balun to coax to the tuner (coax is > > > the only acceptable line into the shack)? The shack is a > > > metal building 30X60' and directly below the tower. > > > There is no way to get ladder line to the operating position > > > since all cables have to run through a 3" conduit for > > > at least 30'. > > > > > > The tower is a free standing commercial tower made of 4 > > > 20' sections bolted together with a 2 meter and a 440mhz > > > antenna at the top, all ham antennas. > > > > > > Thanks for any advice. Jim > > > wb5oxq______________________________________________________________ > > > Our Main Website: http://www.amfone.net > > > AMRadio mailing list > > > Searchable Archives: > > > http://www.mail-archive.com/amradio@mailman.qth.net/ > > > List Rules (must read!): http://w5ami.net/amradiofaq.html > > > List Home: http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:AMRadio@mailman.qth.net > > > To unsubscribe, send an email to > > > amradio-requ...@mailman.qth.net with > > > the word unsubscribe in the message body. > > > > > > > > ______________________________________________________________ > > Our Main Website: http://www.amfone.net > > AMRadio mailing list > > Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ > > List Rules (must read!): http://w5ami.net/amradiofaq.html > > List Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > To unsubscribe, send an email to amradio-requ...@mailman.qth.net with > > the word unsubscribe in the message body. > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > To unsubscribe, send an email to amradio-requ...@mailman.qth.net with > the word unsubscribe in the message body. > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > To unsubscribe, send an email to amradio-requ...@mailman.qth.net with > the word unsubscribe in the message body.
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