Apologies if this is a dupe, I think the previous reply which I sent from
work bounced as I'm not subscribed to TT from that address.
KI7WX wrote:
>> FWIW, I've used a good log at W6EEN for the last few contest
>> seasons. On 20M Don has "only" a 6L at 105 feet which is not
>> great for close in stuff, but killer on DX. The Log is at 60 feet and
>> has an ~30 foot boom.
Lsica replied:
>Is this the 20 meter monobander at W6EEN that Lew McCoy talks about in
>his book "Lew McCoy Talks About Antennas"?
Yes, there are some nice pictures of it and some of Don's other monster yagis
in Lew's book. It is an excellent antenna for it's intended purpose which is
working DX. It is always a joy to operate from Don's station and I've been
very fortunate to have that opportunity. It really is an education to be
able to flip from antenna to antenna and appreciate in real time how
different arrays function during different conditions.
And continued on with:
> I always thought the
>comparison between an LPDA and a 20 meter monobander was unfair enough,
>but to compare a 60 foot 6 element monobander at 105 feet to a 30 foot
>LPDA at 60 is completely ridiculous.
I must object to your tone and statement as being myopic. Particularly since
your comment has been made without considering the actual meaning of what I
wrote (but rather what you thought you read), nor the context of the
discussion and how it applies to David's initial query. Re-read my note to
David, which he posted to the reflector, and see if you still dissagree with
what was said and still feel my comments to be "ridiculous". I will clarify
below in case I was obtuse in my earlier writings. However I do not think
that was the case.
First, I must say that to my way of thinking it's perfectly OK to compare any
antennas at any time, determine the results of the comparison, and then
comprehend what you have learned. We all do that all the time and it is
great fun. Some folks model, some folks still even build and compare
directly. Sometimes we may even perform a valid comparison and learn
something useful!!
That said, I didn't actually compare the two antennas in question directly as
it's not important to the points which were being made. I would not suggest
that a log periodic is a "better" 20M antenna than the 60 foot long,
optimized six element yagi. Rather, I clearly stated that the long boom
monobander is a killer DX antenna (See the text you quoted). If we look at
raw numbers the monobander beats the LP hands down in every catagory. One
must comprehend, however, that those numbers are not the entire story. Sharp
beamwidth (footprint), high front to back ratios and suppressed higher lobes
are not always desireable. It depends on who you are trying to talk to.
Bigger and higher are not always superior, despite what many have been
conditioned to believe.
It's true in theory and in practice that a good long boom monobander (like
Don's 20M 6L) at a height of 1.6 wavelength will have a significant low angle
lobe which is great for working DX. At the same time, however, the array
which is optimized for DX will not work very well for short distance
communications when the signals are arriving at a much higher angles. It
simply cannot do both jobs. At 1.6 lambda the antenna has very little gain
and may in fact have nulls at the higher angles. This is exactly what you do
not want when you are trying to work domestic stations so using a high, long
boom, yagi is a bad choice. In my prior example for this situation, the log
periodic at 60 feet will in fact significantly outperform the 20M monobander
at 105 feet. It's an obvious and expected result. It doesn't mean the LP is a
"better" 20M antenna and that was never implied. It does mean (as I did
clearly state) that paper gain and patterns at arbitrary heights are not the
only factors one must consider when planning an array and choosing antennas.
Using the real world example where one antenna is something many of us would
drool over and the other is rather ho-hum simply serves to illustrate the
point that when you are planning arrays you must keep in mind the purpose of
that array and choose the best antenna for the job. Although many dream of
monster yagis at high heights, they are not always going to be the best
choice.
I hope that is more clear and would enjoy hearing the logic behind counter
arguments as I firmly believe the above to be true. If I'm wrong then I'm
more than willing to learn something new.
Best,
Mark Curran
KI7WX
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