Michael:
I have a D40 up at 78 feet. I followed the instructions to set the
resonant point at 7.090 MHz. When I got the thing up on the mast, low and
behold, it was right on the money. Just follow the printed instructions for
setting the element lengths and you'll be ok.
CC suggest you use solid dielectric coax and not foam so that you can
run full legal power and not have to worry about the center conductor of the
coax migrating out of the dielectric. Remember - the balun is eleven (I
think) turns of RG-8 wound in a circle of 6 inches in diameter. If you were
to use foam coax, this dielectric might soften under heat from QRO and the
center conductor might then spring out and short against the shield.
Can't help you with the anti-sag. My D40 droops about two feet at the
ends. (No juvenile jokes, please!) If you want to try a support truss,
check out http://www.cushcraft.com/support/pdf/d4.pdf . It's the manual for
the D4 (40/20/15/10) but the D4 has traps and needs a truss cable.
BTW, wind the balun in a neat solenoid, i.e., on a (removable) form of
some kind, not random wrapping it into a circle like a hank of rope. Better
RF choking effect that way. (Check out TT archives for multiple discussions
of coax baluns.) I wound my balun separate from the main coax and installed
a PL-259 at the end. Then I joined it to the main coax with a barrel
connector and taped that whole connection.
BTW2, you might want to consider taping the hose clamps on the tubing
sections. This was suggested by several folks here on TT and I followed
their advice with my D40. This will (hopefully) minimize the corrosion of
the clamps and let me disassemble it more readily. Use good quality tape
like Scotch 88. And CUT the tape ends, don't pull the roll to stretch and
tear it.
73 de
Gene Smar AD3F
-----Original Message-----
From: Michael Hatzakis, Jr <mike@hatzakis.net>
To: TOWERTALK@contesting.com <TOWERTALK@contesting.com>
To: <towertalk@contesting.com>
Date: Monday, April 07, 2003 9:48 PM
Subject: [TowerTalk] Cushcraft D40
Just got a Cushcraft D40 to go on top of my Steppir at around 75'. A few
novice questions.
First, trying to tune it prior to installation. A few feet above the
ground, it's resonance is 6.8mhz, about 8feet (on one tv antenna pole) it's
resonance is 7.00 mhz when it is set per instructions to the length
indicated for 7.140 (mid-point). How high do I need to get it to get a
realiztic read on it's resonance point?
Second question, the instructions say, no foam coax for the balun, why is
this? All I had handy in my shack was RG-8x, which I think is the foam
type...
Third question, can someone send me a photo of how they re-inforced the ends
of the elements to reduce sag?
Thanks, Michael K3MH
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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