TT:
This weekend I (almost) finished assembly of the Bencher Skyhawk that
will go up on the tower mid-week. I have the boom leaning up against the
tower, with the front (Dir end) of the boom upward (the only way I could
orient the thing and thread it through the tree branches on the way up). I
just have to install the three reflectors before we hoist it upward.
My problem with the antenna is this: The overall lengths given in the
Skyhawk manual seem OK for the reflectors and the 20M DE, but the dimensions
for the 15 and 10 DEs and all three Dirs seem short. In fact, the 10M Dirs
(there are 2) seem REALLY short (listed as 11-feet, couple of inches).
However, when you add up the lengths of the tubing pieces that comprise each
element, these length totals seem more reasonable.
Question for TT: Do the following dimensions, which I obtained by
adding the lengths of each element's tubing sections, seem reasonable for a
Yagi of this design? They seem OK to me.
BAND REFL DE DIR (dimensions in feet)
20M 37.51 34.73 31.38
15M 24.07 23.06 21.67
10M 17.52 17.28 16.29 16.43 (second Dir at front of
boom).
I realize that I didn't include info on taper schedule or element
spacing, but are the above dimensions at least reasonable?
Question 2: Anybody have a good way to test the choke balun that came with
the Skyhawk? I tried to test the balun by clipping a small 47 Ohm resistor
to the balun wires, connecting my MFJ-259 to it through an unknown length of
50 Ohm coax, and running my MFJ through the HF range. I was able to read
low SWR (1.3:1) ONLY below about 12 MHz. Once I reached 14 MHz and up, the
SWR climbed to over 2.5 and showed considerable reactance swings. Might
this phenomenon be due to the possibly-inductive resistor I used, and the
resultant excursion the line and load took as they scampered around the
Smith chart with changes in frequency?
Thanks for any insight you folks can send my way.
73 de
Gene Smar AD3F
P.S. The Skyhawk was a lot of fun to build. Each element came out of its
own individual bag and went together pretty easily. The boom is almost 100%
double sleeved (two feet at either end are only single-walled boom
material). Elements are all insulated from the boom, though, so I'll have
to think a bit about shorting the non-DE's to the boom for tower loading on
80M.
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|