[Antennas] 1/4 wave vert - elevated radials

Fri Aug 22 20:27:35 EDT 2008

Shunt is similar to Gamma match...and on grounded verticals it would be good
(allows the tower to be grounded for lightning protection) but narrows
bandwidth over a series fed radiator....ask the AM broadcast folks...(which
I am part of :) To series fed it would require it to be totally isolated
from ground..buried in concrete would probably work but I would be worried
about lightning exploding the concrete in a direct strike if not
grounded....OR insulate all three of the legs but if it's in the air, that's
kinda hard to do :)
Guy wires MUST be broken up to non resonant lines..do NOT just go with one
egg at each end...YOU could use the guys as top loading and break them half
way down (and I would!)..thus giving you more effective loading and better
radiation efficiency...but DON'T just break them at top and bottom...I would
break them in the middle as well...
As for sway, I had a friend (N5DNG, SK) who had 150ft of 25G properly guyed
with DUAL long booms for VHF and UHF (including a J Beam stack he could
rotate from horiz to vertical at the top!) and no sway...use the poly stuff
which doesn't break down in sunlight (UV rays play hell with Dacron or
Nylon...don't use it) OR stranded stainless guys..nothing cheap if you want
it to stay up
Radials? As much metal and as long as you can get it...that's the rule of
thumb...AM stations use 120 1/4WL but that because they are using ground
wave at MF....for HF and SW, big whoop...the 120 radials won't help on the
ham bands...Don't bulldoze the trees if you don't have to, just bury the
radials around them :) Trees won't affect the radials...
Chris
WB5ITT
former CE of the former KLIF, 1190 DFW (with 12 tower night pattern ;)
-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of Eric Jones
Sent: Friday, August 22, 2008 11:18 AM
To: Joe; Terry Conboy
Cc: antennas at mailman.qth.net
Subject: Re: [Antennas] 1/4 wave vert - elevated radials
de N4TGC Eric
Hi, guys: I'm new to this list, so I don't know what subjects have already 
been "dead horsed", but here goes my scenario:
I have a 53' Rohn 25-grade (i.e., light-duty, triangular, tubular-leg) tower
that will eventually (hopefully, before I get too old to climb it) be 
extended to ~85'. Currently it has only lightning rods, one off each leg 
about a foot out - i.e., no radials, as it was a TV and 6-meter-beam tower 
originally. Two basic questions: ARRL pub'ls recommend shunt feed up the 
side, similar to the slant-wire feed mentioned - has anyone tried this, and 
how well did it work? Secondly, I read recently that breaking the guys up 
into non-resonant sections with insulators is not really necessary; that one
"egg" each at the tower end to decouple it is all that's needed. I've been 
using a combo of steel guy wire, grounded to the tower, on the lowest trio 
and para-cord higher up, but I'm concerned that a taller tower will sway too
much (esp. with me on it!) using stretchy dacron/nylon/whatever-it-is line. 
At 60' total it seemed okay, and has been up over eight years that way, but 
is now due for guy replacement.
As for ground radials, I'd only have a problem installing them when the 
red-clay ground is summer-dry (can't effectively be dug by hand), and 30' to
the north where there's a tree line. While I'm currently using one of the 
trees for a guy tether, I could bulldoze the whole line back about another 
20'. The other tether points are the facia on my workshop, and a 
purpose-built stanchion/clothesline pole. Yeah, I had to wet the ground to 
dig that one in!
 TIA e