[TowerTalk] Cushcraft 40-2CD (2 element yagi) - Capacity hat blew off in wind - story

[Alan Higbie]

My 2 el. 40 has been up since about 1997-ish.

Right at the start I made the Dave Leeson (W6NL) high wind modifications.

In mid-2016 the beam was off the tower and mechanically checked
(thanks K7NV).

Exactly 4 years ago (Jan. 2017) the beam survived very high winds
which gusted to 105 mph. The G-1000 rotor did not survive, but the
beam was undamaged. It was scary to watch.  Replaced rotator with
G-2800.

In mid-November 2020 some high winds blew off one of the capacity hats
(from one side of the reflector).

I found the essential parts, and replaced some missing hardware. With
help from K7TD, the capacity hat is now back where it should be.

The other 3 capacity hats were checked - and one of the others was
loose and about ready to blow off too.

Hardware was all tightened, taped and sealed with clear coat (to
protect tape from UV). Loctite applied to mounting hardware.

What was the effect of missing a capacity hat from the reflector? I
suspect it altered the electrical length and therefore probably
changed the F/B ratio.

Unfortunately, I didn't run any rigorous local line-of-sight F/B
tests.  However, turning the antenna 180 degrees while watching a 40
meter CW signal from 1500 miles away failed to demonstrate any F/B.
Anecdotal "evidence."

For what it's worth, here are the SWR curves for this antenna --
before vs. after SWR curves run on K3_EZ software.

73, Alan K0AV

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 SWR CURVE --- *BEFORE* reflector's capacity hat was replaced
    |
    |---|----+----+----+----+----!----+----+----+----+----|----+----+----+----+----|
SWR:|
4.0 +
    |
3.8 +
    |
3.6 +
    |
3.4 +
    |
3.2 +
    |
3.0 +
    |
2.8 +
    |
            *
2.6 +
    |
2.4 +
    |
       *
2.2 +
    |
2.0 +
  *
    |
1.8 +
    |
1.6 +                                                               *
    |
1.4 +                       *
    |             *    *         *
1.2 +        *                        *    *                   *
    |
1.0 +   *                                       *    *    *
    |---|----+----+----+----+----!----+----+----+----+----|----+----+----+----+----|
mHz:   7.00                     7.10                     7.20
           7.30

11/17/2020 8:22:27 AM     NOTES:

Frequency     SWR
---------     ---
007000000     1.0
007020000     1.2
007040000     1.3
007060000     1.3
007080000     1.4
007100000     1.3
007120000     1.2
007140000     1.2
007160000     1.0
007180000     1.0
007200000     1.0
007220000     1.2
007240000     1.6
007260000     2.0
007280000     2.3
007300000     2.7

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SWR CURVE --- *AFTER* reflector's capacity hat was replaced

    |
    |---|----+----+----+----+----!----+----+----+----+----|----+----+----+----+----|
SWR:|
4.0 +
    |
3.8 +
    |
3.6 +
    |
3.4 +
    |
3.2 +
    |
3.0 +
    |
2.8 +
    |
2.6 +
    |
2.4 +
    |
2.2 +
    |
            *
2.0 +
    |
       *
1.8 +
    |
  *
1.6 +                                                               *
    |                                                          *
1.4 +                                                     *
    |   *                                            *
1.2 +                                           *
    |
1.0 +        *    *    *    *    *    *    *
    |---|----+----+----+----+----!----+----+----+----+----|----+----+----+----+----|
mHz:   7.00                     7.10                     7.20
           7.30

1/6/2021 2:35:07 PM     NOTES:

Frequency     SWR
---------     ---
007000000     1.3
007020000     1.0
007040000     1.0
007060000     1.0
007080000     1.0
007100000     1.0
007120000     1.0
007140000     1.0
007160000     1.2
007180000     1.3
007200000     1.4
007220000     1.5
007240000     1.6
007260000     1.7
007280000     1.9
007300000     2.1