>In a message dated 99-01-02 13:21:28 EST, k3gt@pgh.net writes:
>
>> Would like comments about the KLM 10-30 Log Perodic. Only have 22.2 SQ
>> Ft of allowable wind load on the tower and already have a Hygain 402BA
>> up. Or...what would you put up to have 40 thru 10 on 1 tower with the
>> windload?????
>
then de K7LXC
> Do you want to have performance on 40-10 or just have an 'average'
>signal? IMO LP's are NOT optimized for ham band performance but for broad
>spectrum coverage.
>
>
Over 13 years ago, amid mirth and much joking, I put up a KLM 8-el
7-30 mhz" skip-frequency LPDA. Much was said locally about the lousy F/B,
low gain, poor DX performance, and Lexan insulators that fall off from UV
exposure. I did this to compete on a lower budget with my neighbor and QSL
manager K7UP, who had 2 towers and monobanders for 40-10m. My KLM went up,
with some needed improvements to the overhead support system, at 75', the
mean height of his array of Hy-Gain monobanders. Our QThs were 1 km apart.
Over 3 years of joint DXing, with the same amps running well below
1500w (Drake L-4Bs), we explored virtually all openings, long and short
paths, to every possible part of the globe. We entered contests and worked
major Dxpeditions. What we found out of this subjective testing was this:
roughly %75 of the time, I would hear a given DX station earlier and later
in the opening than his mononanders, well enough to put it in the log whan
he could not. At the peak, he would get a better report, usually 1 s-unit or
so. %25 of the time, the role was reversed. To help trying to rule out other
causes of this observation, we tried different radios and feedlines ( I use
190 ft of Andrews 7/8 hardline now, as a result of the extra testing).
My LP is still up after 13+ years, after one 114 mph major wind
storm, and several other powerful storms. And the Lexan insulators, exposed
to all that UV in the New Mexico desert, still have not failed. The only
failure was a cracked ferrite balun one winter.
Looking at the real-world performance, the LPDA enabled me to have
longer openings and work more DX than K7UP, most of the time. His station
has performed better than average in numerous ARRL and CQ contests, so it is
no slouch in itself.
Now we can all point to advertised gain figures and other
smoke-and-mirrors, and we can talk about feedline losses, front-end
performance, and perhaps technique. Lotsa variables here. But for me, these
are the salient points in a real-world comparison:
1) The LPDA has perhaps 5 dBd gain from 14-28 mhz, less on 40/30m.
2) The LPDA has only about 3 S-units (whatever they are..) F/B. At
my NM QTH; this was no big deal as I rarely had big QRM areas off the back
of my antenna.
3) The H-plane (ie, vertical) 3-db beamwidth on the LP is from 0 deg
to roughly 70.
If this last point is true, and I believe it is, then if you compare
the patterns of the 2 over real ground at the same height, the LP still had
real gain at all other arriving waveangles for which the monobander did not.
Hence the band was "open" for me to add DX to the log when it was not on
that monobander.
This anecdotal summation is not offered in the sense of scientific
and repeatable proof. Rather, in the day-to-day usage of our stations, it
provides an interesting and unexpected result which "conventional wisdom"
showered heaps of doom and prophecy of failures upon the project before it
even got started.
And by the way, the mirth and joking was rather quickly seen to
disappear in the face of improved DX results.
And it was a vast and obvious improvement over the Telrex TB5EM that
was up for years before the LP.
Not scientific, of course, but it worked for me. And that is the
point. We endevour to improve our station in life (pun intended) as best we
can.
BTW, that 114 mph peak wind (and over 90 sustained) was verified;
that storm brought down the county sheriff and fire comms tower, as well as
several towers and antennas in the area. The KLM (with my improved support)
was un-bowed and unbroken. Specific tower details available upon request
(direct), and film at eleven....
I suggest Mr Stahl & Co "done good" with that model...
Respectfully, and HNY,
Jim, KF7E, 5X1XX, 7Q7JH, et al
Jim Henderson
jhenders@zianet.com
jhenders@swlink.net
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