--------- Begin forwarded message ----------
From: "Jim Jorgensen" <jim_jorgensen@qmgate.anl.gov>
To: "Fred Hopengarten" <k1vr@juno.com>
Subject: Re: TopBand- New antenna on
To: <topband@contesting.com>
Date: 25 Jul 1997 16:06:55 -0500
RE>>TopBand: New antenna on loaded tower
7/25/97
Fred,
I've been watching this discussion go back and forth and decided to
comment.
I run the following system:
Tower is 85 feet of Rohn 45 with insulated guy wires and 15 feet of mast.
The
mast supports: KT34-XA at 85 feet, Cushcraft WARC-band rotatable dipole
at 90
feet, and 2-L Hy-gain 40-meter yagi (can't remember the model, but the
Hy-gain
yagis are at DC ground) at about 98 feet. The tower also supports: 160
meter
inverted V at 80 feet, 75 meter inverted V at 75 feet, 40 meter inverted
V at
60 feet, and two 75/80 meter 1/4-wave slopers at about 75 feet. I shunt
feed
this whole mess with a shunt wire (#10 house wire, pulled tight, no
suppports
except top and bottom) spaced about 30 inches from the tower and
connected to
the tower at the 70 foot level. I use nothing but a variable capacitor
in
series with the shunt wire at the base. The capacitor is rated about 300
pf
at 9KV and can be remotely tuned from the shack with a 1-RPM motor (so I
can
cover the whole band 1.8-2.0 Mhz with 1:1 SWR). The tower is about 40
feet
from the house and all the feedlines, control cables, etc. were just laid
on
the grass and allowed to disappear into the sod with time.
I can offer the following observations: I have no problems with RF
getting
into the shack from the feed lines of the other antennas. The top
loading of
the various junk is no problem (in fact, I have concluded it might
actually be
good) except for the 160-meter inverted V. If this is coupled into the
system, the electrical length seems to be too long and the system becomes
difficult to tune. (I don't know how the radiation performance is
affected.)
I decouple the 160-meter inverted V with a homebrew resonant balun made
in the
following way: I have about 30 turns of RG-8 wound onto a 4-1/2 OD
length of
PVC and use a stub of RG-8 (around 200 pf, I think) as a capacitor to
resonant
the shield of the coil of RG-8 at 1830 Khz. This completely decouples
the
160-meter inverted V as if if were not there. I have found that
conventional
baluns (e.g., ferrite beads over the coax, or other types) will not work
to
decouple wire antennas from the shunt fed vertical. They will just heat
up
and waste power. I learned this the hard way when I melted the choke
balun on
the 160-meter inverted V while calling TO0R last winter.
So, does this antenna work? You'll have to ask my competition, Fred. I
have
232 confirmed from Illinois. If you find this interesting and useful,
you can
copy it to the reflector if you wish.
73,
Jim, K9RJ
--------------------------------------
To: <topband@contesting.com>
Date: 7/25/97 3:37 PM
To: Jim Jorgensen
From: Fred Hopengarten
From:
Fred Hopengarten K1VR 617/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address: fhopengarten@mba1972.hbs.edu
On Thu, 24 Jul 1997 11:11:10 EDT k4pi@juno.com writes:
>"HAM RADIO" MAY 1975 W4OQ "SHUNT FED VERTICAL ANTENNAS".
Mike: I have the article. My problem is that I have a ton of stuff on
my tower, up and down. Like: TH6/TH6/TH7 at 97'/61'/31' (61' on
homemade rotatable sidemount). Plus 40-2CD at 90' on RingRotor. Plus 160
inverted v dipole at 88'.I think my electrical height is over 5/8, and
may be 3/4 wavel;ength, for all I know. The problem is that the W4OQ
article doesn't help you calculate elec wavelength for an antenna mounted
in the middle or along the way. It also does not answer the question:
Do I move my gamma rod out or in, up or down, once I've started. I
already use an omega match, and 68 radials, but I'm convinced that I
haven't hit the "sweet spot" yet, and nothing I've ever read tells me how
to find that sweet spot.
Thanks for the tip, though. I remain hopeful.
Fred K1VR
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To: k4pi@juno.com
Cc: topband@contesting.com
Subject: Re: TopBand: New antenna on loaded tower
Message-ID: <19970724.163046.8215.30.k1vr@juno.com>
References: <199707231740.KAA18632@linda.teleport.com>
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From: k1vr@juno.com (Fred Hopengarten)
To: <topband@contesting.com>
Date: Thu, 24 Jul 1997 16:37:25 EDT
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