[TowerTalk] XM240 Results

[AA4NC@aol.com]

Thanks to some hard work by the PVRC/NC tower Krew (or is it a posse? my hip
hop speak isn't too good...K4MA, K4HA, KS4XG, NT4D), we took down a lightning
damaged 402CD and replaced it with a XM240. My hat's off to Cushcraft -
somebody has finally listened to the people who put up and use these antennas.
They got it right on this one. I believe that they have addressed almost all
of the mechanical shortcomings of the 402CD, and kept the great electrical
performance in the process. The 2.5" (Cushcraft Viagra) boom is so rigid I
think you could easily use it without a top truss, even though they give you a
Phillystran truss. For those who are going to put a 2L40 on a ring rotator,
this is your boy.

I hacked my own dimensions to make the resonant point 7.100. This worked well
with the 402CD, and appears to work well with the XM240. With no other
antennas at the top of my tower, the 240 covers the whole band at less than
1.9:1 VSWR (as measured on an Autek WM-1 and my Yaesu FT990's SWR meter. My
MFJ 259 analyzer shows 2:1 points at 7.007 and 7.265.
The half element dimensions used were:
Reflector: 21'-9"
Driven El: 20'-11.5"

Thanks to WE9V and KG9X for pointing out typo mistakes in the manual. 
(Length EB is 45", NOT 41" as shown)
(The driven element measure is from the edge of the aluminum, not the element
center as it is on the reflector).
My antenna alignment for the elements and boom were right on, so maybe the
problems they had with boom alignment were due to a very early production run.

With the antenna by itself on the tower (@ 120'), a quick 100 watt trial
produced a huge pile of Europeans this evening. I didn't have any other 40m
antenna to compare it to, but it sounded like it was working well. I'll know
more when I repair the old 402CD which I plan to stack with the XM240.

Thanks again to the installation Krew and the Towertalkians for their hints &
kinks...

73,

Will AA4NC / W4MR

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