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
> >> >
> >>
> >> _______________________________________________
> >>
> >> _______________________________________________
> >> TowerTalk mailing list
> >> TowerTalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|