[TowerTalk] KLM 10-30 Log Perodic

[Eric Gustafson]

Hi Steve,

Sorry it took so long to bet back to this.  Comments below.

>From: K7LXC@aol.com
>Date: Sat, 2 Jan 1999 14:22:49 EST
>
>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?????
>
>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.

I'm not quite sure what you mean by "optimized" in this context.
But judging by the results of your own Yagi comparison test
measurements, you could say the same thing about tribanders.

The Log Periodic is not "optimized" for a particular frequency
because it is completely unnecessary.  The Log periodic is
"designed" to provide a certain level of performance (so many dB
gain, so many dB front to back) over a specified range of
frequencies.  If properly designed, it holds the gain performance
+/- about half a dB and the F/B performance +/- 2 dB or so over
the entire range.  A typical triband Yagi doesn't even do that
over an entire _band_.

Normally, the only "optimization" that is done is at the lowest
operating frequency.  Here, in order to save and additional
element (and the biggest one), a shunt hairpin inductor and
adjustment of the longest element length is used to maintain the
performance down to the bottom of the range in the absence of
another element and the extra boom that would be required if this
were not done.

It has been my experience that when installed in the real world
and coupled to whatever random stuff is in the locality of the
antenna, log periodics come _much_ closer to performing as they
are supposed to (without adjustment) than do tribanders or even
single band yagis that aren't adjusted to account for the vagaries
of the particular installation.  By "perform" in this context I
mean gain and F/B ratio.  Not coincidence of minimum SWR and the
desired operating frequency.

I sure hope that in the next series of comparison tests, a
representative set of log periodics can be included.  These
measurements would open some eyes or confirm some long held
beliefs.  Either outcome would be useful.

Snip...

>For further information on multi-band yagi performance, try our
>on-the- air antenna test report. It's 60 pages of data sets,
>summaries and protocol and is available from Champion Radio
>Products (http://www.championradio.com or 888-833-3104). Fifteen
>bucks + s/h.

I have now had time to review this report.  It is very useful and
the methodology was basically sound.  Its definitely worth the 15
bux.  My two main suggestions for future efforts of this kind
are:

1.  Use a much shorter separation distance between test and
    reference antennas.  Somewhere in the 3 to 10 wavelengths
    region (on the lowest band) should be more than enough.  

2.  Include a couple of the commercially available Log Periodic
    antennas that cover the same frequency range as the
    tribanders for comparison.

73, Eric  N7CL

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