FW: [TowerTalk] FW: Help - 80m 4 square
N2TK
n2tk@idsi.net
Thu, 24 Dec 1998 12:31:44 -0500
-----Original Message-----
From: mpride@us.ibm.com [mailto:mpride@us.ibm.com]
Sent: Wednesday, December 23, 1998 6:56 AM
To: n2tk@idsi.net
Subject: Re: [TowerTalk] FW: Help - 80m 4 square
Hello fellow 80 M 4 SQ. user,
Will describe mine and give you some performance numbers. I was
considering changing over to something you are describing, but after
speaking with Jack, W1WEF who has done something similar, I decided to not
change. (I was going to run a test, comparing the 4 SQ made from the
towers (described below) and this wire type around a 100 ft. tower and if
it turned out to be the same or better, then I would take those towers down
and build 2 verts for 160M) Jack says his is not as effective as it
probably could be. Gonna change 1/4 wave lines, tune them up a little
better, etc.
As to mine: Use 4 elevated verticals made from 10 to 15 ft of Rohn 25
(used different heights here due to varying ground terrain), then homemade
insulators and use 40 ft. of Rohn 25 above the insulators, finishing the
vertical with some alum. tubing, overall height (ground to vertical tip
about 85 ft.). Have one set of insulated guys supporting the vertical (at
the 40 ft. level). I have 8 elevated radials on each element. Feeding
each vertical with CATV 3/4 in. hardline, so with velocity considered, it
is longer than it needs to be, to reach the individual elements from the
center of the array.
Tuned each element about 100 KHz below the frequency of interest because,
according to Comtek, this is the way to counter the mutual effects.
What I see with on-the-air tests is about an S-unit (5 to 6 dB gain) over a
2 element parasite wirebeam at 80 ft to Europe (I am not convinced the wire
beam is all that great into EU). The other directions appear to behave the
same. It definitely has gain and is much better for listening (no real
good space for a Beverage and it appears to be very good in this case).
Off the back, I see typically 20 dB F/B and off the sides, about 10 dB F/S.
It is the best antenna on the property for me on 80 M. Also have a 2
element wire beam going south (95 ft), which is a real killer to the
caribbean and SA. The 4 Sq. doesn't quite beat this wire beam, but is a
little better to the deep SA stations (suspect the angle from the 4 SQ. is
too low).
My guess on your situation is probably what you already suspect- get those
elements more vertical. Too much cancellation happening being so close at
the top. Another thought - maybe your tower is resonant on 80 M and is
killing the performance, but I would think an indication of this problem
would show up if the 4 SQ. didn't tune properly - but that is not the case.
Regards,
Mark, K1RX
"N2TK" <n2tk@idsi.net> on 12/21/98 07:33:59 PM
To: towertalk@contesting.com
cc: (bcc: Mark Pride/Bedford/IBM)
Subject: [TowerTalk] FW: Help - 80m 4 square
Presently I have a 4 square based on the article in section 6.3 of ON4UN's
Low Band Dxing, 2nd edition.
I have 4 posts with a vertical wire from each pulled up to the top of the
80' tower. I am using 1/4 wave 70 ohm feedlines to the Comtek box. I have
one radial on each leg pointing away from the tower. There is a current
balun at each feed point.
The differences being -
- the vertical wires are tied into the tower at 80'. This adds more slope
to
the vertical wires.
- the radials and the feedpoint are 12' off the ground
- the vertical wires and 1/4 wave coax are cut for 3.65MHz
- the one radial on each leg is cut to for minimum dumped power at 3.79.
- I switch in a coil in the radial at each leg to have minimum dumped power
at 3.520.
Performance - about 10-18 db f/b and very slight gain over a Cushcraft AV80
36' vertical with 4 elevated 1/4 wave radials.
My questions on trying to improve performance
- Thought performance would improve by making the verticals more vertical.
I
can do that by making them
"T's". The vertical portion would be about 45-48' before I added the T.
- Or I could put up aluminum verticals at each post. Thought was to use 8'
pieces of 2" tapering down to 3/4".
- With the radials, do you think I would get a measureable improvement by
either adding one or two more per leg? What about the articles on 1/8 wave
radials? Would that work with a coil?
- Is performance suffering by cutting the verticals and 1/4 wave matching
lines for 3.65 and then switching in a coil in the radials for phone and
cw?
Tnx for any ideas and input. As to not clutter up towertalk, you can send
direct to me any responses and suggestions and I will summarize on
towertalk
Tony N2TK
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