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[TowerTalk] Min spacing to 80m yagi ?

To: <>
Subject: [TowerTalk] Min spacing to 80m yagi ?
From: "Jim Thomson" <>
Date: Sat, 9 Oct 2010 20:01:07 -0700
List-post: <">>
Date: Wed, 6 Oct 2010 17:57:50 -0400
From: <>
Subject: Re: [TowerTalk] Min spacing to 80m yagi ?

Placing antennas at right angles often worsens interaction problems.  There 
should be little interaction between 40m and 80m if they're pointing in the 
same direction, but who knows what interaction the boom will cause if one is 
rotated.  The only way to tell is to take the time to model the system - 
modeling software is very inexpensive.    Your proposed spacing is very 
close and your mast has a lot of antenna load, hopefully it's not a 2" mast.

John KK9A

##  I had a full size 2-el 80m  with the 5-el  20m   at various distances  
below the 80m,
modeled....and the full size 80m  really screws up the 20m badly !    The 20m 
is screwed
up, even when it's a full  30' below the 80m yagi.   It's actually the worst, 
when it's  10'
below the 80m..and slightly 'better' when it's 7' below the 80m.  F/B, gain, 
F/S all degrade badly.
3db BW is wider too !      But this is not a full size 80m yagi we are 
proposing, so it's apples and oranges.
If the proposed 80 and 20m booms are at right angles, the 36' boom  from the 
80m yagi will screw up
the 20m yagi. The 35' boom from the 40m yagi will also screw up the 20m yagi, 
if the 2  are at right angles. 

##    With everything pointed the same direction,the 40m  won't affect the 
20m..... nor will the 40m affect the
80m.  The 80  won't affect the 40m.   One possible way out of any 80/20 m 
interaction is to  open off both els of
the 80m, each  with a spst-NC  ceramic vac relay..when operating on 20m.   The 
plan was to use vac relays on both
80m els anyway...and run a coax + balun to  the 80m REF.  This way the tuning 
of the 80m REF can be checked, and
ditto  with the 80m DE.  The proposal was to use Tornado drives on both 80m 
els, and 2 x mating controller box's,
the box's have 10 x pre-sets each.  They also have a 4 x digit, digital turns 
counter.   The Tornado drive is just
a pair of  motor driven compressible coils, driven by a threaded delrin rod 
lead screw.  The stock  F-12,  3/8" AL  tubing coils
are not used  The coils are at the feedpoint of each 80m ele.  The controller 
has a 'park mode',
where it fully compress's both coils, and re-sets the counter to zero.  They 
use plastic coated 1/4"  AL  refrig tubing for
the coils, so even when bunched up, the turns won't short out.   On paper, the 
2-el 80m yagi should cover  400 khz  of 
the 80m band..with  high F/B, F/S  and low swr.  It would be a lot of tedious 
tweaking, initially, but at least it can all
be done  from the shack, and with the 80m ant at full height, VS  tower fully 
nested, and hrs on end with a man lift/
crane / bucket truck.  

##  per the ARRL  mast software, the 2" OD x  3/8" thick, 107 ksi chromolly 
mast is good for 101 mph...and 108 mph using
the older EIA-RS-222-C  method.  [eles of all 3 x yagi's  broadside to the 
wind].  With all 3 x booms broadside to the wind,
it's 117mph / 125 mph. Highest gusts here in the last 50 yrs was 72 mph...and 
that was 10 yrs ago.   Rotor is a small
K7NV prop pitch, with his far out super mast clamp.   I replaced the F-12  
'easy on' mounts with  my own version, using
3/8" thick  6061-T6 plates...and also  3 x DX-eng.. 'super duty saddle clamps' 
, so nothing will slip on the mast. I also
used the same dx eng super clamps  on the boom as well.  A torque compensator 
was installed at the REF end of the 
20m boom.  On paper, all 3 x ants  should be torque balanced.   They will also 
alternate sides of the mast. 

##  One other option I have is to mount the 20m yagi on a 1032 tic the 
72' level.  That would provide 28'  spacing 
to the 80m yagi... but is a pita.   I have 2 x spare  1032 rings. 

Jim   VE7RF     

To: <>
Subject: [TowerTalk] Min spacing to 80m yagi ?
From: "Jim Thomson" <>
Date: Wed, 6 Oct 2010 05:34:21 -0700
List-post: <">>

How close can you get a 20m yagi, below a 2-el  80m yagi ?
I have an option to use a F-12  Sigma  280-S  shortened 80m yagi
at the top of the mast, with the F-12  340N  at the bottom of the mast.
Spacing between the two of them would be  10.5'    If possible,  I
would like to sandwich my  F-12  520  [20m yagi]  between the
80 and 40m yagi.    Apparently, you can mount any other F-12 HF
yagi within 36"  of the 3-el  340N yagi.    If I put the 20m yagi
4'  above the 40m yagi... that would leave  6.5' between the 20m yagi
and the 80m yagi.   Will this work ??    If it doesn't, one option is
to remove the 20m yagi.   Another option is  to  place the 80 and 40m
yagi's at right angles to each other [ no 20m yagi at all] .   I don't think
is required, but would minimize the total wind load.

 Plan B  would be to replace the 2-el 80m yagi with a
80m rotary dipole...with dipole inline with 20m/40m booms  below it.  IE: 
is then at right angles to both yagi's below it.   Due to  day time height
the above options are strictly an after dark scenario.   I don't have any
software on hand
to model any of the above.

Thanks.... Jim   VE7RF 


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