Interesting that the Antenna Book does not specify if this is physical or
electrical length. Your guess is as good as mine. (Unless I missed the
reference.)
73 -- Larry -- W1DYJ
-----Original Message-----
From: Doug Turnbull
Sent: Monday, February 29, 2016 13:58
To: 'Jim Thomson' ; towertalk@contesting.com
Subject: Re: [TowerTalk] Radial question
Dear OMs and YLs,
Yes all this is true but do not forget the actual radial length will be
shorter than 0.4 Wavelength when on the ground. It may be electrically 0.4
wavelength but physically it is considerable shorter as the ground changes
the velocity factor.
73 Doug EI2CN
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Thomson
Sent: 29 February 2016 18:07
To: towertalk@contesting.com
Subject: [TowerTalk] Radial question
Date: Sat, 27 Feb 2016 11:52:14 -0500
From: "Larry Banks" <larryb.w1dyj@verizon.net>
To: "Vincent Weal" <vincek4jc@gmail.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Radial question
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
### see B above. Note in the case of 120 radials, like for AM broadcast,
they are .4 wave length long
( 4/10)...and NOT .25 wave. You will see the .4 wave long radials in
all the eng books too.
## If I have the story correct, the reason why you require longer radials,
when more and more are used ,
is the distance between the far ends of adjacent radials, for optimized
operation, can only be a certain max distance.
## with only 16 radials, that adjacent distance between far ends of
radials will be exceeded, if longer than .1 wave length.
Ditto with 36 radials + .15 wave lengths. That is also mentioned on the
W8JI site.
## Some will also use a ground screen at the base of each vertical, + the
XXX number of radials....with radials attached
to the base ring, at the base of each vertical. The ground screen is typ
a grid affair, like wire mesh, ranging from aprx
4x4 ft.... up to as big as practical, like 20 x 20 ft. IE: ground screen
laid down 1st..with XXX radials laid over top of the
grnd screen / mesh.
## So if 120 radials are used, they should be 110 ft long for 3600
khz..... and 220 ft long for 1800 khz.
## IMO a single 80m vertical, with a modest radial system eats up a lot
of space. 4 x phased 80m verticals,
even with a modest radial system, will eat up one helluva lot of real
estate, and more if longer radials used.
Any vert array is still gonna be noisy on RX, so RX ants will be
required..and located away from the vert array.
## At that point , depending on local icing condx, I would opt for a 80m
rotary dipole, or a 2 el 80m rotary dipole.
## VE6DX works EU on 75m SSB, like a machine gun...with his hb 2-el 75/80m
yagi.... with 66' els..and on a
28 ft boom. His tower is only 14 ft from his property line..hence the 28
ft boom. Check out his construction
series on his website. Very impressive, for a tiny postage stamp sized
lot, in a crowded neighbourhood.
http://www.qsl.net/ve6wz/intro.htm
Jim VE7RF
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