Let me describe what I've done to make a tower radiate. The tower is 11
sections of Rohn 25 with a tapered top section with a chrome-moly mast
supporting a single 48' long boomed, 10 element 6M antenna on top...making
a total of 12 sections. Its guyed every 30' with Phillystran. The base is
a 3' tall section set in a 3X3X4 base of concrete.
I cut 4 radials of 12 GA. stranded, insulated wire, each being 130'
long. By scampering up and down the tower I found a "sweet spot" using a
SWR "analyser" where attaching the center conductor to the tower and the
braid to the now elevated 4 radials I obtained a broad SWR null centered
on 1830 or so. I let the radials simply hang down limply from the
attachment height (at the 40' level)...where they hung right next to the
tower for about 10' or so then gently angled away from the tower at about
10-15 degrees or so. If I pulled them away from the tower, then the 1.5 :1
SWR would degenerate rapidly to well above 3.0 : 1.
The radials, after drooping to the ground then run along the surface
of the ground in 2 cases and along the top of bramble-berries and bushes
and stuff in the other 2 cases out in 4 separate directions
In daytime tests, this tower hears distant AM broadcast stations at S5
where a inverted V broadside to the station can't hear it...So it looks
like it at least hears in a vertically oriented fashion. The real test
will be whether the distant stations can hear this thing as compared to
the inverted V or other "known radiators" of the shunt-fed or inverted-L
species.
Any guesses as to what this thing is closest to?..elevated radial
vertical...tuned multi-sloper....giant dummy load..??
I'll be plaguing people for comparisons when the time and band permits.
73 and I remain,
Lew
Lew Sayre W7EW/W7AT lew@teleport.com
P.O.Box 3110 Fax 503-391-2258
Salem, Oregon 97302 160M thru 1296MHz
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|