Hi Vince,
This is from the ARRL antenna book:
------------------------------------------------
Practical Suggestions For Vertical Ground Systems
At least 16 radials should be used if at all possible.
Experimental measurements and calculations show that with
this number, the loss resistance decreases the antenna efficiency
by 30% to 50% for a 0.25 wavelength vertical, depending on
soil characteristics. In general, a large number of radials (even
though some or all of them must be short) is preferable to a
few long radials for a vertical antenna mounted on the ground.
The conductor size is relatively unimportant as mentioned
before: #12 to #22 copper wire is suitable.
a.. If you install only 16 radials they
need not be very long - 0.1 lambda is sufficient.
b.. If you have the wire, the space and the patience to lay
down 120 radials (optimal configuration), they should
be 0.4 lambda long. This radial system will gain about 3 dB
over the 16-radial case.
c.. If you install 36 radials that are 0.15 lambda long, you will
lose 1.5 dB compared to optimal configuration.
---------------------
73 -- Larry -- W1DYJ
-----Original Message-----
From: Al Kozakiewicz
Sent: Saturday, February 27, 2016 11:40
To: Vincent Weal ; towertalk@contesting.com
Subject: Re: [TowerTalk] Radial question
I'm sure it will make a difference. The question is will it be perceptible?!
With ground radials, it's a situation of diminishing returns (# and length).
A rule of thumb is that the radials should be at least as long as the
antenna is high, though I have no idea if this "rule" is based on real
physics or what.
Like the magic 120 radials for AM broadcasting....it's not that 120
represents some kind of gold standard but is, I believe, simply a regulatory
threshold that allows an applicant to skip a lot of engineering and field
observations in a license application. 60 radials may work just as well
given local soil conditions and terrain, but use 120 and you don't have to
prove it.
Al
AB2ZY
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Vincent Weal
Sent: Saturday, February 27, 2016 10:50 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Radial question
I'm installing a 40/80 meter vertical (DX Engineering 8040VA-1) which calls
for 65 foot radials. However, I recently saw a video of an antenna
presentation by W3LPL in which Frank suggests 70 foot radials for an 80
meter antenna. I'll be burying the radials about an inch in the ground.
Will it really make a dime's worth of difference whether I cut the radials
at 65 ft or 70 ft? My understanding of radials has always been that elevated
radials should be cut at a quarter wave plus 5%, but ground radial length
isn't critical. I just wanted to get a consensus before I start chopping up
thousands of feet of wire.
(Yes, I am burying the radials because the guy who cuts my lawn will
annihilate anything in his path. He even once managed to destroy an inverted
vee that was 40 ft in the air!)
73, Vince K4JC
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