I dont remember the details from NEC, Dean Straw, N6BV, did the modeling
when he lived in the next town.
All I can say was that going elevated made a huge performance improvement.
Carl
KM1H
----- Original Message -----
From: "Tim Duffy K3LR" <k3lr@k3lr.com>
Cc: <towertalk@contesting.com>; "Barry Kirkwood" <barry.kirkwood@gmail.com>
Sent: Monday, July 23, 2007 3:18 PM
Subject: Re: [TowerTalk] 160m Inverted L
> Better ground conductivity would help the raise the efficiency of an
> antenna
> using a raised radial installation (with 4 radials 15 feet off the ground
> for
> 1.8 MHz) more than one using ground mounted radials (30 or more that are
> 1/4
> wavelength long at 1.8 MHz).
>
> This has also been confirmed while comparing NEC models of both antenna
> systems.
>
> I am curious what do your models using NEC show over your ground?
>
> 73!
> Tim K3LR
>
> jeremy-ca wrote:
>
>> Frank has the good fortune of having decent ground conductivity, not all
>> of
>> us have that luxury.
>>
>> Carl
>> KM1H
>>
>> ----- Original Message -----
>> From: "Tim Duffy K3LR" <k3lr@k3lr.com>
>> Cc: <towertalk@contesting.com>; "Barry Kirkwood"
>> <barry.kirkwood@gmail.com>
>> Sent: Monday, July 23, 2007 1:21 PM
>> Subject: Re: [TowerTalk] 160m Inverted L
>>
>> > Anyone who is concerned with the difference in antenna efficiency with
>> > respect
>> > to elevated radials VS. ground mounted radials (assuming you have a
>> > choice)
>> > should re-read Frank, W3LPL's excellent post last year here on
>> > TowerTalk.
>> > It concerned his 160 meter 4 square array and the real world
>> > operational
>> > difference he noticed when he converted from elevated radials to ground
>> > mounted
>> > ones.
>> >
>> > I know he is not sorry that he made the change.
>> >
>> > 73!
>> > Tim K3LR
>> >
>> > jeremy-ca wrote:
>> >
>> >> My take on the subject from many years of 80/160M operation at
>> >> different
>> >> locations is as follows:
>> >>
>> >> Superb to very good ground such as a salt water marsh, a fresh water
>> >> swamp
>> >> with plenty of dead vegatation (gooey muck). Anything works, 4 to 16
>> >> 1/4
>> >> wave radials is fine, more cant hurt but dont go overboard. 4' ground
>> >> rods
>> >> at the ends and at the base.
>> >>
>> >> Good to average ground as in a midwest farm field. 32 to 64 on ground
>> >> radials, 128 is overkill.
>> >>
>> >> Poor to average ground. 64-128 on ground radials, maybe a ground
>> >> screen
>> >> within 30-50' of the base. Consider 30-40 elevated radials if
>> >> possible.
>> >>
>> >> Very poor ground, most of New England, etc. Dont waste your time with
>> >> on
>> >> ground radials unless there is no other choice. 30-60 elevated radials
>> >> and
>> >> even a ground screen if feasible; this is becoming a popular choice
>> >> among
>> >> AM
>> >> broadcasters either installing a new system or having found their 50
>> >> year
>> >> old buried radials have become one with Mother Nature.
>> >> The FCC has actually asked some stations to reduce power since their
>> >> proof
>> >> of performance field strength with elevated radials is actually higher
>> >> than
>> >> their as new buried system.
>> >>
>> >> Im a big fan of elevated radials since I live on top of a ridge;
>> >> granite
>> >> has
>> >> poor conductivity! At a prior location with damp but sandy soil a
>> >> ground
>> >> screen made a huge difference when placed over 60 on ground radials.
>> >>
>> >> At the cottage in Maine 100 yards from the ocean I use only a 50' long
>> >> ground screen covered with 1/2' loam and reseeded. Thats almost the
>> >> size
>> >> of
>> >> the available open ground. The antenna is 50' of mast with a 4 wire
>> >> top
>> >> hat
>> >> and a coil at the base to complete the required resonance. With a
>> >> shielded
>> >> loop for RX that setup has worked a few new ones when Ive had to be
>> >> there
>> >> for family reasons.
>> >>
>> >> The fencing sold at garden centers works well. Get the type with a 2 x
>> >> 4"
>> >> mesh that is welded, then galvanized and then plastic coated. Peel off
>> >> enough plastic to solder to and seal the joint with automotive
>> >> undercoat,
>> >> roofing tar, etc. I found my mesh (5 50' x 4' rolls) in a local
>> >> weekly
>> >> Want
>> >> Advertiser, it was one year old and like new and 1/3 of new cost.
>> >>
>> >> Remember that the better the ground the lower the angle for maximum
>> >> gain
>> >> up
>> >> to almost the free space model. This may become self defeating since
>> >> some
>> >> DX
>> >> comes in at angles above 40* or so. I worked 3Y0A some years ago (1989
>> >> or
>> >> 90) on 160 with an inverted Vee at 60' apex. It took all of one call
>> >> in a
>> >> monster pileup.The operator later told me at Dayton I was way above
>> >> the
>> >> din.
>> >>
>> >> Carl
>> >> KM1H
>> >>
>> >> ----- Original Message -----
>> >> From: "Barry Kirkwood" <barry.kirkwood@gmail.com>
>> >> To: <towertalk@contesting.com>
>> >> Sent: Monday, July 23, 2007 10:20 AM
>> >> Subject: [TowerTalk] 160m Inverted L
>> >>
>> >> > FWIW:
>> >> > Talking the 160m problem:
>> >> > The subject of counterpoises, ground planes etc is a subject in
>> >> > itself.
>> >> > My 02c worth:
>> >> > There are two main questions:(a) How to configure the
>> >> > antenna/earth/radial
>> >> > etc system so as to get current flowing in the thing.
>> >> > (b) What the effect of the environment (salt water, seaside,
>> >> > mountain
>> >> > top
>> >> > etc) and whatever arrangements conspire to get most of the radiation
>> >> > at
>> >> > a
>> >> > reasonably low angle.
>> >> > My limited experience: Made an inverted L out of my 50ft tower and
>> >> > tribander
>> >> > plus a 20ft topmast of alumin tube. One thick insulated wire run up
>> >> > tower
>> >> > and off the top of the top mast (up 70ft) and tied off to tree. Gave
>> >> > 150ft
>> >> > wire in all (about 80ft in the L loading wire, sloping down to about
>> >> > 50ft
>> >> > high at end.
>> >> > Fed with gamma match wire connecting at 40ft level, held off 3ft by
>> >> > spreader.
>> >> >
>> >> > Tried loading against a collection of maybe 16 random length
>> >> > radials,
>> >> > most
>> >> > only 50-60ft. Had little joy until I made two radials like a 160 m
>> >> > low
>> >> > dipole, snaked around my boundary fence and one leg along top of
>> >> > fence
>> >> > of
>> >> > kind neighbour. Grid dipped to 1830. Connected to the braid of coax
>> >> > at
>> >> > feedpoint.
>> >> > Series variable C feed to gamma wire.
>> >> > Effect was obvious and immediate. Thing tuned up, could bring swr to
>> >> > 1:1
>> >> > by
>> >> > adjusting C and fiddling gamma match spacing from tower.
>> >> > Should mention my ground quality very poor.
>> >> > Did not connect the random radials.
>> >> >
>> >> > This set up could work Eu from ZL whenever they could be heard.
>> >> >
>> >> > My take on this: Get some part of the system that you know is
>> >> > resonant
>> >> > in
>> >> > band, maybe even one 1/4 radial would do. Then there is a good
>> >> > chance
>> >> > that
>> >> > the rest of the system will tune up against it.
>> >> >
>> >> > Of course if you can come up with a great radial system ,the above
>> >> > would
>> >> > not apply.
>> >> >
>> >> > Quarter wave inverted Ls may not be the greatest, but given a
>> >> > reasonable
>> >> > earth system give a good bang for the buck. Get the impression that
>> >> > most
>> >> > users are reasonably pleased with them.
>> >> >
>> >> > --
>> >> > Barry Kirkwood PhD ZL1DD
>> >> > barrykirkwood@gmail.com
>> >> > _______________________________________________
>> >> >
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > TowerTalk mailing list
>> >> > TowerTalk@contesting.com
>> >> > http://lists.contesting.com/mailman/listinfo/towertalk
>> >> >
>> >>
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>> >
>> >
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>
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