Hi Terry,
I believe that radials 16" deep will be great for lightening protection, but
not for RF -- they should be on or near the surface. As for how many, this
is a good reference, 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: Terry Brown
Sent: Wednesday, May 09, 2018 18:38
To: towertalk@contesting.com
Subject: [TowerTalk] Ground question
I am putting in a fairly short tower in my backyard; 35ft of Rohn 25g.
I will have 3 ground rods around the base. The tower is next to my house so
my ground radial field will be semi-circular.
I will be putting 8 ft ground rods every 16 ft. My lot is about 35 ft. deep
so radials will be 32 ft. Long buried about 16 in. Underground.
1. How many radials do I need and
2. What gauge solid copper wire.
Where we live in Western Oregon does not get much lightening. My antenna
will be 10-12 ft. Above the highest point of the roof.
Thanks for the help.
Terry de N7TB
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