[TowerTalk] Log Periodics & 2 Element Beams--Stacked

[K7GCO@aol.com]

In a message dated 12/9/00 1:02:43 PM Pacific Standard Time, K7GCO writes:

<< In a message dated 12/9/00 8:42:43 AM Pacific Standard Time, 
aa4nu@ix.netcom.com writes:
 << 
  >I know of no one stacking 2 element beams.  K7GCO
  
  F-12 certainly seems to have had success with their C3 and related models.
  The F-12 basic C3 series are 2 element per band interlaced yogis ...
  Many contest stations have found that a 2x stack of 2 element 40m
  yogis offer more performance options ... than a single 3 element yagi.
  So perhaps there's more "2 elements beams" in use today than in years
  before, and in stacks at that ... ?
  
  73 Billy AA4NU
  
   >>
 Billy: Thanks for the input.  I had one other tell of 2/2/2.  I was thinking 
of 2 element quads and typed beams.  I also had in mind one banders only as 
multi-band 2 element beams have other elements that are longer that could 
enter into a "balanced interference" if the spacing is optimized for the 
middle frequency.  I'll model this and check it out.  I knew I could find and 
bring previous or current installations to light.  I'm curious as to the 
suggested spacing and by whom.  Have you seen patterns, can you switch 
between them and what have you found?  Have you had higher gain beams stacked 
and been able to select either for comparisons?  I've pointed out before that 
the lower the gain of the beam the closer the spacing for the cleanest 
pattern without ears.  Further due to the wider vertical patterns and closer 
spacing, they interfere some with each other when used individually.  
 
 I had 2-3 element vertically polarized quads stacked and could select either 
or both in the shack with my matching and selection system.  Neither was 
head-on individually but head on together.  The mfg initially used too wide a 
spacing and it had 2 ears.  I spaced them closer 1' and got a nice clean 
pattern.  It's also shows this in Eznec very clearly and yet those who have 
done neither test deny this is happening for reasons--best known to them.  
When used vertically polarized on a horizontal boom, this is a good way to 
compare 2 beams on "distant repeaters" (Canada) with the least tower 
interference.  I've had 2 higher gain beams with wider spacing still head on 
when selected individually.  In Puget Sound there are too many reflections 
for a good pattern test using close repeaters.
 
 One of my goals is to have the top beam tuned for max gain and the bottom 
for best F/B to increase the performance difference between.  There are many 
advantages being able to select a beam of high F/B for receive only or 
transmit or both.  I have a 3 element 10M yagi tuned for absolute max gain of 
10 dBi on a .35 WL boom with 8 dB F/B, narrow band width and 6 ohms in the 
center of the DE.  I don't feed it there but at the 50 ohm point in a sort of 
a sneaky way with no RF spill over.  I have a way to broadband it now.  This 
is a killer beam-both ways.  It blows them away on 10M and it's so nice to 
have a beam with high F/B to select on receive now with the bands really 
open.  A few years ago when there were few signals on the air there was 
rarely anyone on the back so lack of F/B was not a problem.  When bands are 
closing there are seldom signals on the back so it's a very useful design 
I've found.  It tends to keep the frequency open also.  It's a very "quiet 
beam on the back" with low F/B in another sort of way) and I'm not talking 
about noise.  There is something new in beam techniques every once in a 
while.      
 
 When beams are stacked vertically there is far more advantage to select the 
upper and lower beam individually with my simple switching harness that also 
gives additional bandwidth when both are used.  There is less advantage the 
lower the gain of the beams as they need progressively closer spacing.  The 
spacing widens noticeably as the number of elements or gain increases if 
properly spaced.  Anyone else with 2 element one band beam (only) stacking 
experience?   K7GCO
 
 
 In a message dated 12/9/00 9:42:11 AM Pacific Standard Time, 
coneal@ma.ultranet.com writes:
 << 
  "cost.  Stack spacing is a bit closer also than the big ones.  I know of no 
  one stacking 2 element beams.  K7GCO " 
  
  In 1992 I put up a 2 over 2 stack of the Cushcraft shorty 
  40's.  One at 130 ft and the other at 65 ft.  They exceeded
  my expectations on performance and usually beat full
  sized 3E yagis in the pile ups. One interesting note.  The F/B
  ratio of one antenna is 10 - 15 db and in the stacked configuration
  the F/B of the stack is 25 dB+  !!!!  It also modeled out this way
  as well.  I have a BIP-BOP-TOP-BOT switch and both in phase
  is always better, except both out of phase is needed for local
  (within 300mi.) contacts.  Within a a radius of 200 mi or so, the BOP
  is 20+ dB better.  The bottom 2E is fully rotatable with a ring rotor.
  73,
 Chuck...K1KW
 
 Chuck:  This is a great system.  Write it up for one of the mags.  It 
verifies what I have been claiming for "2 element beams."  2 element beams 
shall rise again.  K7GCO >>

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