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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