[TowerTalk] 160m Inverted L

[jeremy-ca]

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 at gmail.com>
To: <towertalk at 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 at gmail.com
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