[TowerTalk] About to pull the trigger

[Tom McDermott]

> 1. AN Wireless tower, 90', heavy duty, rated at 36 sq.ft
>   2. M2 40M4LLDD at 90'
>  3. 2 x KT36XA at 100' and 60'
>  4. Prosistel PST61D + Green Heron to rotate the 40m beam and the upper tribander
>  5. K0XG ring rotator + Green Heron for the lower tribander
>  6. W3NQN bandpass filters sandwitched between 2 SO2R switches to provide SO2R filetring
>  7. BIP/BOP stack controller for the KT36XA tribanders
>  8. SO2R switch for all antennas
>  9. On 80m, Comtek dipole 4sqr as in http://www.comteksystems.com/4square6.html
>  10. On 160m, shunt feed the 90' tower
>  11. RX antennas- 2 two-way beverages


Built almost this same setup in 1984 using Rohn 45 (different rotators). Comments:

2. I don't know if there have been mechanical improvements in the 4M40 since 1984. Referencing
the older design: the element clamps on the 4M40 came loose. Use 3 stainless hose clamps.
The clamps usually have a small hole, drill a matching hole in the boom and pin one clamp of each
element to the boom with a #6 sheet metal screw.  Most of the linear-loading insulators broke. Replace
them.

3. The 4M40 at 90' heavily detuned the KT34XA at 102' on 15m. The 34XA was poor on 15m to
begin with, near the 4M40 it became totally useless. A 15m dipole at 20 feet was 30 dB better, literally.
I added a gray (UV resistant) PVC dummy element near the front end of the 34XA to balance the wind
torque, worked great. Rebuilt the 34XA with the rebuild kit in 1996 to fix the 15m problems, but they
got worse instead. The 36XA may have these issues dealt with, I'd check it carefully before putting it
up on the tower.  The 34XA at 102' worked great on 20M and 10M. Had a 20' 3" steel mast (210 
pounds). It was 8' inside the tower and 12' outside the tower. Used a chain hoist to raise and lower
the mast to get to the top antenna, recommend using a high quality one for positive control. Added a
second clamping arrangement inside the tower to hold the mast while raising or lowering. It was loose
when the rotator was in place.

4. First rotator (HDR-300) lasted 14 months, as totally destroyed as a rotator can get. Second rotator
was an Emotator 1300 and a home-made torque isolator using a BMW transmission-to-drive-shaft
rubber donut described in the Dave Leeson's Physical Design of Yagi antennas book.
Good idea, worked great.

5. Did not use the lower antenna much at all, finally removed it. I was not trying to operate SO2R
however. It did not provide any benefit working the Carribean from North Texas compared to the
high yagi.

9, 10 Shunt fed the tower on both 80 and 160. Worked well for DX on 80, not as good stateside. Very
good Tx antenna on 160m. Ended up with a 15kv vacuum variable and stepper motor combo to tune the
antenna. On 80M it would tune 3.5-4.0, on 160M I added a 4:1 transformer and used the same tap
point (12.5 ohms on 160 => 50 ohms on 80) it would tune 1.8 to 2.0.  Transmitting variable breadslicer
style capacitors with 3.5kv rating arced over at 1500 watts.

When I moved a couple of years ago, the neighbors were concerned I might remove the tower. It was home
to red-tailed hawks, large owls, etc. and most of the neighbors liked the bird watching and did not want to
see the antennas or towers go. The buyer wanted the towers and antennas, so they remained.

Would I do it again?  You bet.

    -- Tom, N5EG


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