Your 80M example with a toploaded 70 ft tower and 60 ft attachment
is very similar to my 80M sloper success with an 80 ft tower / TH6.
To scale that to 160M would require a 140 to 160 ft tower with
twice the capacity hat (perhaps a wide spaced full size 3L40).
IMHO, emphasis on opinion, you can't make a 160M sloping wire
work in the *same manner* on an electrically short tower with a
smaller capacity hat. You CAN make such a tower work as
a shunt fed vertical or elevated GP.
To determine EXACTLY what is going on,
it is necessary to model the system which
can be done (with some effort and time) using
existing software such as EZNEC, etc.
I think this horse has been beaten to death :-).
Tom N4KG
On Wed, 2 Jan 2002 "MGB" <mgb4@address.com> writes:
>
> Stephanie,
> Normally I don't say much on these reflectors because there are
> too many
> "experts" standing by waiting to tell me the theory of why my
> antennas don't
> work. Here are my experiences with 80 Meter quarter wave slopers. I
> have a
> 70 foot Rohn 25 tower with an 8 foot mast. A CushCraft D3W is
> attached to
> the mast at the 77' point. A TH7DX is attached to the mast at the
> 72" point.
> My four 80 Meter slopers are attached to the tower at the 60' point.
> Each
> sloper is 67' of insulated copper wire oriented NE - SW -NW- SE. I
> switch
> between wires using a DX engineering antenna switch box. Each sloper
> is
> attached to assorted supports on the bottom end, but most are in the
> 10-15'
> height range. At the base of the tower I have a #2 wire radial ring,
> which
> I've attached about 50 quarter wave radials, and just laid them on
> the
> ground. In about 2 years the grass grows over them and they
> disappear. In my
> case there is nothing magic, just hook the sloping wire to the 60'
> point on
> the tower. The center conductor of the coax is attached to the
> sloping wire
> and the braid is attached to the tower. One trick I've found
> effective is to
> have the upper insulator no more than 3/4" from the attachment
> point. The
> closer the better. This antenna functions like a off center fed
> vertical, in
> that the tower is the main radiator. NOW..the problem you are having
> with
> 160 meters is somewhat more complex, in that you don't have the
> height to
> effect a 50 ohm match as easily as 80 Meters. The trick here is to
> find the
> match point on the tower. I would suggest attaching the 160 Meter
> sloper to
> the 35' height as a starting point. Stretch the 135' +- length of
> wire out
> and attach the other end to a 20' +- support. This is a VERY tricky
> operation in that there is NO "SET" "magic" attachment point on 160.
> You're
> just going to have to keep trying different attachment heights, and
> end
> heights. If you do find the "sweet spot" it will work like a charm!
> On 80
> meters I have worked about 320 countries and it is HEAD and
> shoulders above
> my other 80 meter antennas. If you don't already have one, purchase
> a Alpha
> Delta sloper or at least look at one to get the idea how to arrange
> the
> attachment point. he uses a simple aluminum plate with an so-239
> connector
> and a hole in the plate which is placed under one of the tower leg
> bolts.
> Its super simple but 320 countries on 80 tells the story. If you
> need
> further help please write.
>
> 73 & GL Mick W4YV
>
>
> ----- Original Message -----
> From: "Stephanie WX3K" <wx3k@ptd.net>
> To: <W8JI@contesting.com>
> Cc: "Towertalk" <towertalk@contesting.com>
> Sent: Tuesday, January 01, 2002 1:17 PM
> Subject: RE: [TowerTalk] Half slopers using a tower
>
>
> >
> >
> >
> > -----Original Message-----
> > From: Tom Rauch [mailto:w8ji@akorn.net]
> > Sent: Tuesday, January 01, 2002 7:50 AM
> > To: Towertalk; Stephanie WX3K
> > Subject: RE: [TowerTalk] Half slopers using a tower
> >
> > <snipped>
> >
> > Please explain what "5 or more above" implies.....There have been
> many
> > others that have shared some very good results with the HALF
> SLOPER
> antenna.
> > Sounds to me like this antenna is anything but a "free lunch"
> antenna.
> > Taking the time to understand the functionality of an antenna is
> well
> worth
> > its weight in gold to me, even if it means a little extra
> experimentation
> > initially.
> >
> > Besides isnt that the whole fun of the technical side of amateur
> radio
> > ??????
> >
> > Stephanie R. Koles WX3K
> > wx3k@arrl.net
> > http://www.qsl.net/wx3k
> >
> >
> >
> > >If you want a vertical, install a normal vertical like an
> Inverted L fed
> > >at earth level and a good radial system, or shunt feed the tower
> and
> > >use a good conventional radial system with it. it might be a
> little
> > >work, but you will be 5 or more above any of the "free lunch"
> > >systems that rarely if ever work as expected.
> > >
> > >
> > >73, Tom W8JI
> > >W8JI@contesting.com
> >
> >
> >
> > This list is sponsored by the new eHam.net Store. When you buy
> products
> > like ICE filters, Array Solutions StackMatch, or M-Squared
> Antennas from
> > the eHam Store for the same price you pay direct, a portion of the
> sale
> > price goes to support this list. Check it out at
> http://www.eham.net.
> >
> > -----
> > FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> > Submissions: towertalk@contesting.com
> > Administrative requests: towertalk-REQUEST@contesting.com
> > Problems: owner-towertalk@contesting.com
> >
> >
>
>
>
>
________________________________________________________________________
> This list is sponsored by the new eHam.net Store. When you buy
> products
> like ICE filters, Array Solutions StackMatch, or M-Squared Antennas
> from
> the eHam Store for the same price you pay direct, a portion of the
> sale
> price goes to support this list. Check it out at
> http://www.eham.net.
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/web/.
________________________________________________________________________
This list is sponsored by the new eHam.net Store. When you buy products
like ICE filters, Array Solutions StackMatch, or M-Squared Antennas from
the eHam Store for the same price you pay direct, a portion of the sale
price goes to support this list. Check it out at http://www.eham.net.
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|