[TowerTalk] Radial length
Larry Banks
larryb.w1dyj at verizon.net
Sat Mar 15 15:33:52 EDT 2008
My understanding is that the linear distance between radials determines
ground resistance which needs to be minimized.. This is why more radials
continue to be useful when they are longer. The shorter the distance from a
point in the ground where RF hits to a radial the better. 120 radials can
be longer because the distance at the tips is much smaller that would be the
tip distance for 16 radials at the same length.
As to the pattern of radials -- and I can't remember the reference but I
think it was in QEX -- not having a "perfect circle" is OK -- it just skews
the beam pattern. toward the direction with the densest radials.
73,
Larry
W1DYJ
----- Original Message -----
From: "Robert Carroll" <w2wg at comcast.net>
To: "'Towertalk'" <towertalk at contesting.com>
Sent: Saturday, March 15, 2008 2:23 PM
Subject: Re: [TowerTalk] Radial length
> The general sense of the discussions I have read is that the intent of the
> radials is not to provide a near perfect reflecting surface under the
> antenna, but to provide a ground return with as little loss as possible.
> If
> I were going for something that in the extreme would look like an almost
> perfectly reflecting copper sheet under the antenna, I would use the same
> angular spacing between each pair of radials. On the other hand if I were
> only trying to provide a low loss ground return, I might route the radials
> for convenience in avoid things like a garden, a pool, or some other
> object.
> Which view is the correct one?
>
> 73
> Bob W2WG
>
> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Larry Banks
> Sent: Saturday, March 15, 2008 1:42 PM
> To: donovanf at starpower.net; Towertalk
> Subject: Re: [TowerTalk] Radial length
>
> Just to close the loop an all of this great info, I will paraphrase from
> the
>
> ARRL Antenna Book, (c) 2007, 21st edition, page 3-9 which matches up
> pretty
> well with all of these comments:
> ----------------------------
> 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 effi-
> ciency 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: <donovanf at starpower.net>
> To: "Towertalk" <towertalk at contesting.com>
> Sent: Saturday, March 15, 2008 1:22 PM
> Subject: Re: [TowerTalk] Radial length
>
>
>> 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 at 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 at gmail.com>
>>>Subject: Re: [TowerTalk] Radial length
>>>To: "Bill Turner" <dezrat at copper.net>
>>>Cc: Towertalk <towertalk at contesting.com>, Tom Osborne <w7why at 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 at copper.net>:
>>>> ORIGINAL MESSAGE:
>>>>
>>>> On Fri, 14 Mar 2008 16:20:13 -0700, "Tom Osborne" <w7why at 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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