Dink wrote:
Using the cumulative brain power of this reflector, what would be your
ultimate system for a single tower? I want this to be as contest
competitive as a single tower can be. Stacks? Tribanders?
Monobanders? Sidemounts? At what levels?
This past summer, I completed what I consider the ultimate one tower
system (at least for me!) My constraints were as follows:
1. Use existing tower - Rohn 45, 76 ft tall (4 ft of bottom section in
concrete), guyed with Phillystran at 2 levels. At top is T2X with 20 ft
high carbon steel mast (80KPSI rating), with the rotor at the bottom of
the top section.
2. Make it work for SO2R
History of tower:
It was put up about 9 years ago, initially with TH7 at the top (76 ft) and
402CD above that (85 ft). For 80, I have a K8UR-style sloper array.
On 160 and inv vee hung from near the top of the tower.
About 5 years ago, I added a second TH7 at 40 ft, on a TIC Ringrotor.
It is phased with the top TH7 using a DX Engineering Universal Phase
Box.
Adding the second TH7 made a BIG difference!
Next goal: Without putting up another tower, create a viable SO2R
station. As an engineer by training (though not vocation), my intent was
to keep to specs, and not overload the tower. I was following the LXC
prime directive, even before we all knew it was called LXC prime
directive :.)
Attempt 1 - I installed an all-band vertical (Hygain DX-77) about 200 ft
from the tower. Also, added ICE 419 bandpass filters to both radios,
and Top Ten Devices six-ways and A/B boxes for antenna switching.
Bottom line - it sucked. Couldn't break a pileup, and sometimes even
with nobody else calling, I wasn't heard. Back to the drawing board...
I was intrigued by the possibility of using F12 C31XRs, which in their
ads say you can feed each band individually. After lots of e-mail back
and forth to a number of individuals (W6XR, W2VJN, and others), I
abandoned this idea because I could not get a firm set of numbers to be
sure that there would be adequate attenuation between two active bands
on one antenna.
So, let's leave the 2 TH7s as is, since they work so well. What about
another tribander (very) low on the tower? First thought was something
small, like a F12 C-3 at 22 ft. I bought EZNEC, read the book, read
the book again, and read the book again (and thanks to Roy and LB for
putting up with lotsa questions too. Also much discussion with Pete,
N4ZR as I plodded through this). I ran a bunch of models, and this
looked like a terrible combination. The interactions of the C3 on the
active stack were bad, and the interactions of the lower TH7 on the
active C3 were worse.
What about another TH7? First order of business, make sure there is
enough clearance under the lower guys (and double check!) Fortunately
there was. Run all the EZNEC models (and rerun them) Stack active,
low antenna inactive, all pointing the same way, all pointed 90 deg apart,
etc. Repeat with low TH7 active, repeat with middle TH7 active, repeat
all three fed together. Do this on each of 10, 15 and 20m. Bottom line-
The TH7s looked good! Minimal interactions.
What about phasing all three, with the option of feeding one by itself (as
in WX0B's Stackmatch)? On 15 and 20 there was NO additional gain
or improvement in pattern by phasing the lowest TH7. On 10m, it was
marginal, so I elected to feed the bottom TH7 alone.
In summary, here's what I have up:
Rohn 45, 76 ft above ground, 2 levels of Phillystran guys.
160 inv vee (Bevs for receive)
80 K8UR-type array, bottom end pulled back to tower base.
40 Cushcraft 402CD at 85 ft
20-10 TH7s at 76, 40 and 22 ft. Top two phased. Bottom one fed by
itself. Top one on T2X (w/402CD), bottom two each rotated on TIC
Ring.
Almost forgot - a 4 el 2m beam at 65 ft for packet.
ICE 419 filters on both radios.
Top Ten Devices six-ways and A/B boxes.
Stubs on both radios 40-10m.
The system works like a champ! The performance of TH7 at 22 ft has
exceeded my expectations. There are times, on 10 and 15, when the
low TH7 outperforms the stack. It even holds its own on 20 while
chasing multipliers. Though I may change something in the future, I can't
imagine what.
73 Barry
--
Barry Kutner, W2UP Internet: w2up@mindspring.com
Newtown, PA FRC alternate: barry@w2up.wells.com
-----Original Message-----
From: BK [mailto:w2up@mindspring.com]
Sent: Tuesday, December 14, 1999 16:44
To: owner-towertalk@contesting.com
Subject: message lost?
Earlier today I sent a reply to K7WA's message to the list. I believe I
put the list address in the CC line by mistake. Can you recover it and
post it for me, or do I need to repost it?
Tnx/Barry W2UP
--
Barry Kutner, W2UP Internet: w2up@mindspring.com
Newtown, PA FRC alternate: barry@w2up.wells.com
--
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