[TowerTalk] FW: F12 Delta 240 performance observation

[KM5VI]

I have an older F12 EF240X beam with linear loading.  I initially found the
F/B performance to be dependent on the tuning of the elements.  I used an
antenna modeling program to find a combination of element tunings that
produced my choice of compromise between F/B, impedance match, and
bandwidth.  I then modeled each element separately to find their natural
resonant frequency.  The next step was to isolate the elements on my F12 in
the air and tune each element to those predicted resonant frequencies.  The
antenna subsequently exhibited a much better F/B performance.  I should add
that it is important to do both the modeling and tuning at the actual
installed height and be sure that the model has sufficient segmentation -
I'm sure there is a lot of advice out there regarding modeling...  

And perhaps someone else on the reflector knows an easier way to tune the
elements and may share that with us.

Hope this helps you in some way.

73
KM5VI


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
john at kk9a.com
Sent: Wednesday, September 19, 2012 11:31 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] F12 Delta 240 performance observation

20dB F/B would be incredible for a short 2el 40m beam AT the resonant
frequency.  You should have adjusted your beam for a higher frequency if
you mostly use the phone band.

John KK9A


[TowerTalk] F12 Delta 240 performance observation
from [SPWoo]	[Permanent Link][Original]
To:	 "towertalk at contesting.com" <towertalk at contesting.com>
Subject: [TowerTalk] F12 Delta 240 performance observation


I have a D240 and I haven't
used it much since I put it up this past spring.  Tonight I decided to
run some performance tests.  I found a DX station and I turned the
attenuator
on such that that my S-meter was reading S9 when the beam is pointed at
him.
When I turned the beam 90 degrees away I saw an S7 which is 12 db less
than the
maximum signal strength.  When the beam was turned 180 degrees away I
saw an S9
which is the same signal strength
as when the beam was pointed directly at him.  I'm a little confused
about
this.  This is
supposed to be a yagi and not a rotary dipole!  The listed spec. for F/B
ratio
is 20db at its peak.  I do know that F/B is not constant across the band
for a
yagi.  What kind of front to
back and side rejection ratios should I expect to see on this particular

antenna?  I haven't asked Mark at F12 about this.  I don't want to waste
his
time until I have more info.  Perhaps I'm missing something on the test
or that
I made an error in my antenna assembly.  Your help on this is greatly
appreciated.  73.


Jonathan Woo W6GX


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