k4sb at comcast.net
Fri May 11 11:21:26 EDT 2007
Just a few comments and I will exclude the original messenger from the
quotes. I am going to assume that the verticals in question are at or
near 1/4 wave long.
First a question and a comment, an unknown writer makes the statement:
with poor reports, running 600 watts. I worked US hams at about 200
miles with good reports. However, I think that I can lay much of the
blame for the reports on the fact that I have a single radial,
shorter than 1/4 wavelength. Once I establish a good mechanical
connection and a reasonable SWR, I will add radials (aiming for 60)...
First of all, that "good mechanical connection" is a necessity before
any work is done on the radial system. Having "a reasonable SWR" has
no meaning or purpose.
I have no personal experience with verticals (aside from engineering
at AM radio stations long ago), but from what I've read elsewhere,
even a single radial is OK as long as it is not buried or on/close to
Whether or not a radial is buried has nothing to do with the
The object of the radial work is to lower the ground loss. I generally
try to fine small insulated wire.
However, when working with Ham Band verticals, I have been under the
impression that a minimum of 4 radial, each 1/4 wave length of the
lowest frequency to be used was a necessity. ( and yes, I understand
that more is usually better, up to a certain point, ) Am I wrong about
the length or does it matter ?
It has been pretty well established that with as few as 4 radials,
making them 1/4 wave long is unnecessary. ( ARRL Antenna Book, Moxon,
ON4UN, KU7G's excellent review published by the ARRL, and many more.
But once it's coupled to the ground, the soil detunes it and ground
losses go way up ... unless you've got a lot of them.
Ground loss is a fixed constant, depending entirely on the composition
of the soil or whatever is under the vertical. Unless you want to
build a hugh salt water pool, radials are much better.
My experience here in Tucson, Arizona has been that burying radials up
to 4 inches below ground doesn't make any difference, I believe that
the dry nature of the local soil to be responsible for the low losses.
I seriously doubt that the dry conditions found in AZ could make for
lower losses. Quite the opposite is more likely.
The solution is to beg, borrow or otherwise scrounge a side walk
trimmer. With it you can easily make very nice, narrow, cuts in the
grass, without any dirt being thrown up on the grass.
This is an excellent idea. I took it one step further, and has a
3/8" steel blade modeled after the original, but straight and sharp
at the ends. I also increased the length slightly so it barely clears
the blade guard.
One last point, the efficiency of a Vertical antenna is a function
of power applied - power lost. Since a 1/4 wave vertical has a
characteristic impedance of around 37 ohms, you can get an excellent
idea of your ground losses by hooking up no radials. Here, such will
give an almost perfect 1:1 SWR. Jumping for joy? Don't. That means you
have about 13 ohms of loss.
One thing which does greatly improve a vertical is if you can raise
the impedance of the vertical. Try a folded dipole, tripole,
arrangement or increase the length of the vertical. The higher you
go, the less influence ground losses have on the system. For example,
I used a "T" antenna, fed with a parallel L/C network, and no radials.
And if you really want to get "grandiose", try flying a full 1/2 wave
vertical supported by a balloon on 160. That antenna will clear the
frequency for good. Unfortunately, RX noise is high, so you definitely
need an aux receiving antenna.
One last thought; and this is the result of experience passed on to
me by a 6 lander. GROUND the bottom of the vertical while on receive.
It may have been K6LL, but whoever it was, he reported a drop in noise
on his RX antenna of 4-5 S units.
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