W8JI posted a classic reply to this question nearly ten years ago.
Not coincidentally, sixty 1/4 wavelength radials have since become the defacto
standard among serious 160 meter DXers.
Here's a brief synopsis, followed by the original text of Tom's original e-mail.
All of these measurements are referenced to the performance of sixty 1/4
wavelength radials. Actual results are highly dependent on your local ground
conditions.
Elevated .03 wl Conventional
four -4.3 dB -5.5 dB
eight -2.4 -2.7
sixteen -.8 -1.3
thirty two -.7 -.8
sixty -.2 reference 0 dB
73
Frank
W3LPL
Subject: TopBand: Elevated GP vs. Vertical Antennas - long
From: w8ji.tom@MCIONE.com (Tom Rauch)
Date: Tue, 17 Mar 1998 18:30:34 +0000
> buck?"... I asked the same question of Tom recently and while I am still
> attempting to parse the various dB's quoted it appears that somewhere between
> 32 and 64 ground radials is the breakpoint compared to 4 elevated radials of
> 1/4wl...
No, here's how it stacked up in dB. 0 dB is the reference of 60
radials. These are farfield signal levels, accurate to + - .1 dB.
Elevated .03 wl Conventional
four -4.3 dB -5.5 dB
eight -2.4 -2.7
sixteen -.8 -1.3
thirty two -.7 -.8
sixty -.2 reference 0 dB
I selected the 60 radials as the reference antenna, so ALL the
measurements are in reference to the field from that system. In
theory, that system is about 1 dB below perfect.
> It appears to me that 8 elevated radials are closer to reality for the average
> topbander than a ground radial system of more than 64 radials....
That would be OK if you accept being about 3 dB or so down. Myself, I
want that 3 dB since it only takes a few afternoons work and $120 or
so of material. That's about the cheapest 3 dB I can buy, since I
have a 1500 watt PA.
Consider this, going from the 3/8 wl vertical to the four square only
gained me 5 dB! I got almost that just by going from four radials to
60 radials.
It is often claimed 120 1/4 wl radials are ideal. Not according to
extensive tests. With 1/4 wl radials, more than 60 offer very little
advantage. The results were:
30 -1.56 dB
60 -.93 dB
113 -.79 dB
The nearest to ideal measured in the famous L, B, and E RCA report
was 113 .412 wl radials. In that test, the end result was 0.2 dB from
perfect! Going from 113 .412 wl radials to 60 .274 wl radials
will cost you all of .7 dB!
By the way, these tests showed a nine foot on a side ground screen
was meaningless when a large ground system was used, but did make a 3
dB difference when only 15 radials were used. But this was for
a short radiator (1/16th wl tall). With a taller antenna the ground
screen would mean less, of course.
Disclaimer:
Other than my own tests, the data above is available in "Ground
Systems as a Factor in Antenna Efficiency" Brown, Lewis and Epstein,
RCA Manufacturing Co. and was printed in Proceedings of the IRE
Volume 25 number six in June 1937. I converted the results into dB
from the published mV/m, so it is easier to follow.
73, Tom W8JI
---- Original message ----
>Date: Sat, 15 Mar 2008 12:34:21 -0400
>From: "Alex Malyava" <alex.k2bb@gmail.com>
>Subject: Re: [TowerTalk] Radial length
>To: "Bill Turner" <dezrat@copper.net>
>Cc: Towertalk <towertalk@contesting.com>, Tom Osborne <w7why@verizon.net>
>
>there is an article (in russian - http://dl2kq.de/ant/3-33.htm) on
>DL2KQ website with MMANA/NEC2 computer analysis of vertical of various
>length like 1/8, 1/4 and 5/8 with radials like 1/10, 1/4 and 1/2 above
>different soil.
>Depends on your soil and vertical height there is different number of
>radials of different length you need to put.
>If you have, for example, 1/8 vertical on medium or good soil you need
>more then 16...32 radials of 1/4 to work better than the same number
>of short 1/10 radials.
>
>K2BB
>
>2008/3/14, Bill Turner <dezrat@copper.net>:
>> ORIGINAL MESSAGE:
>>
>> On Fri, 14 Mar 2008 16:20:13 -0700, "Tom Osborne" <w7why@verizon.net>
>> wrote:
>>
>>
>> >Is it true that my radials only need to be around 100 feet long instead of
>> >125 for full sized 160 meter radials or is that an old wives tale? 73
>> >Tom W7WHY
>>
>>
>> ------------ REPLY FOLLOWS ------------
>>
>> Well, yes and no.
>>
>> If the radials are laid directly on the earth, length is much less
>> critical than if they were up in the air, as in a counterpoise. The
>> missing few feet in your case will be made up by the earth itself, but
>> having almost a full 1/4 wavelength of radials, you may not notice much
>> difference. I'd go ahead and try it.
>>
>> 73, Bill W6WRT
>>
>>
>>
>>
>> _______________________________________________
>>
>>
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