Hi All,
This thread fits perfectly with the radials over the beach thread, and
the Hex beam gain. It fits with the B&W dipole and GAP vertical
stuff also. The quad fits in, as do the bad opinions about the G5RV.
The CFA is this taken to an extreme, of course.
We all love our antennas, and we want to believe in magic.
Factually, things often aren't as "rosy" as they appear.
> Don't lose heart over my comments. Even if the 40M329 has some weakpoints,
> I suspect that between some computer optimization work with the dimensions
> and some mechanical modifications to the element design, you'll be able to
> come up with a real nice antenna. This antenna is pretty old, so it was
> probably designed before people were using NEC and knew about element
> taper corrections.
....and it was done before people cared if baluns really worked
correctly, and when there were no other large yagi's for 40 meters
around.
Just the sheer size of the antenna is worth 20 dB, like it is in a
large poor (30-40%) efficiency Rhombic.
> Jim Lawson, W2PV came out with his papers on the effects of element taper,
> he ended up changing the dimensions on his Wilson 3 element 40 meter yagi
> elements by something like 12" each to make it really play.
By "really play", the gain probably increased 1 or 2 dB. The work is
what made it seem like more. The only big change would be in null
depth, and as almost everyone who owns a Hex beam knows
higher F/B always means at least 3-4 dB gain over what it really is.
> booms, and masts. With an Excel spreadsheet, and the taper schedule from
> the 40M329, you can probably figure out where it will fail, at what wind
> speed it will fail, and how to improve it.
On mine, the elements constantly broke right at the point where
they exited the .058 wall 1-1/2 inch tubing and became that paper-
thin tubing. Every time the wind hit 50 or 60 mph, an element
broke.
I've never had any boom or insulator failures, but then the elements
in mine (and boom) have always been strutted. The only thing I
kept was the boom and the elements out to the first taper point.
The rest is all new 6061 stuff.
I think the antennas with double wall tubing are more reliable, and
it's easy enough to check that out. But after all the headaches I
went through I'd never put one up with the thin single-wall tubing
that has the strength of a wet toilet paper roll.
73, Tom W8JI
w8ji@contesting.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
|