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[TowerTalk] An Opposite View on the Log Periodic vs Selectivity Impact

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Subject: [TowerTalk] An Opposite View on the Log Periodic vs Selectivity Impact
From: DavidC" < (DavidC)
Date: Fri, 26 Nov 1999 22:45:08 -0500
My original question:

> >Since the log periodic is broadbanded does it amplify received
> >signals between the Ham bands along with the Ham band signals and
> >thus place a greater burden on the selectivity and filters of the
> >If not why not, please?  I am just curious since it seems that it would.

The following response came from a log periodic manufacturer.  (I will not
name him at the moment since he hasn't had the opportunity to give me
permission to share this piece from our private E-mail.)

> I don't think this would be the case at all.  In fact it could be just the
> opposite.  Your theory is reasonable but.......  Assume a triband yagi on
> your tower.  As a shortwave receive antenna , it would work quite well
> because of the large capture area.  Lots of aluminum up there.  Let's say
> there is a strong sw broadcast station at 16 MHz.  Your tribander wouldn't
> care too much which direction the 16 MHz signal came from because it is
> directional at 16 MHz.  It could conduct a pretty strong 16 MHz signal
> towards your radio.   Now consider your new log periodic, which all your
> buddies will envy......    It probably has a larger capture area as far as
> lots of aluminum is concerned, because it has more elements.  BUT, it will
> be directional as far as 16 MHz is concerned.  If the 16 MHz signal is off
> to the side or to the rear, there could be much less signal passed towards
> your radio.

I am beginning to see a case of neutralizing advantages and disadvantages.

The yagi has been represented as less-resonant on non-Ham frequencies
and thus less likely than the logs to gather those signals ... in the
it is pointed ... sort of like a tuned circuit is frequency selective.

But the yagi makes no intentional design effort to be directionally biased
against non-Ham frequencies off the side and back and as a "big hunk of
aluminum" may grab signals off the side and back that the log would reject.

The log is intentionally directive across all design frequencies and is thus
more discriminating from the sides and back against all signals in the
design range.  However from the direction the log is pointed it will amplify
all signals, desirable or not, in its path and within its design range.

Sounds as though either beam design may serve well in opposite
I guess we are back to the quality of the rig and any tuned circuits between
it and the beam we choose.  Yes?

Comments or clarifications?  Thanks! & 73, DavidC  K1YP

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