[AMRadio] 160 meter antenna


Jay Bromley jayw5jay at gmail.com
Mon Jan 12 21:21:30 EST 2009


Yes Ken you are correct about the detuning skirt.  In fact mono pole here 
has a detuning skirt around the tower.  I am also familiar with the climbing 
safety lines.  You can tell the difference in that most detuning skirts I 
have seen on Cell mono poles had several wires around the pole coming down. 
Also you will see quite a bit of insulators and hardware compared to a 
simple safety line.  However that last time I was there the fiberglass 
housing the vacuum capacitor had been damaged by hail.  So it was full of 
water.  Very sad deal.  However I don't think they need it any more.  The AM 
station was right next to this moved across the river.  After they put on 
the mono pole it caused a problem with the AM station's pattern.  So up went 
the detuning skirt that looks much like the Folder Unipoles, hi.

73 de jay/w5jay..




>I would bet that the Skirt type antenna that you describe is actually a 
>detuning system on a cellphone tower that is within two miles of a 
>Directional AM Broadcast array. If the Cell tower is within the two mile 
>range, the company who owns it must have a partial proof of performance 
>done on the AM directional array before and after the tower is built. If it 
>is shown to distort the pattern, then the detuning network that you see is 
>added and tuned to make the cell tower invisible electrically to the AM 
>array at the broadcast frequency.  It actually is an "untenna" I guess.
> Ken Zuercher KC8QO
>
>
> --- On Mon, 1/12/09, robertcharles at att.net <robertcharles at att.net> wrote:
>
>> From: robertcharles at att.net <robertcharles at att.net>
>> Subject: Re: [AMRadio] 160 meter antenna
>> To: "Discussion of AM Radio in the Amateur Service" 
>> <amradio at mailman.qth.net>
>> Date: Monday, January 12, 2009, 3:36 PM
>> 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
>> <bguyger at 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: "robertcharles at att.net" To:
>> w9gt at 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, robertcharles at att.net wrote:
>> >
>> > From: robertcharles at att.net
>> > Subject: Re: [AMRadio] 160 meter antenna
>> > To: cozy659 at 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
>> > > >
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