Topband: Inverted L

[w2pm at aol.com]

ZL2HAM Wrote:

-----Original Message-----


>>  From: Rick Kiessig <kiessig at gmail.com>
To: Jwpjj at aol.com; topband at contesting.com
Sent: Tue, 4 Nov 2008 2:06 am
Subject: Re: Topband: Inverted L

John,

4 radials isn't anywhere near enough (unless they're elevated).  SWR 
doesn't
tell you anything about antenna efficiency.  Ideally, you want to keep
adding radials until your feedpoint impedance levels off.  A good 
antenna
analyzer (like the AIM 4170B) can be a big help.

The easiest way I've found to optimize your radials is to walk around 
the
area where your antenna is, and place a small marker every 0.015 
wavelengths
(2.5 meters for an antenna on 160), up to about 0.25 wavelengths away 
from
the antenna.  Then run radials to those markers, so that the tips are 
0.015
wavelengths apart.  Space the radials out evenly if you would rather do 
the
work a little at a time.  If you're limited by the amount of wire you 
have,
make the radials shorter, but keep the tip spacing at 0.015 wavelengths.

As you add radials, ground resistance will go down, antenna efficiency 
will
go up, and SWR will probably also go up.  Use an L-network (or 
variations)
or a tuner to match the antenna to your amp/rig.

73, Rick ZL2HAM

W2PM Responds:

I have 32 mostly 1/4 wave radials laid out about 200 degrees around the 
base - I cannot get to the other side to complete the circle because of 
property boundaries and grouchy neighbors.  Laying these out in a neat 
radial field made a huge difference here.  Before I took the time to 
lay these properly,  I had all sorts of wires running random. Some were 
short, many 1/4 and perhaps about 22.  The 10 additional radials I 
added when I redid the field were mostly short, 1/8, but the 
performance of the antenna went up considerably.  And on 80, (I have a 
trap at 65 ft on the vert section) I break any pileup Ive heard on 75 
phone first or second call.  And on poor nights I am often the only 
station DX hears.  With the old messy radials I was no where near as 
competitve.


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