[TowerTalk] 80 Meter yagi question

[StellarCAT]

I have a F12 Magnum 180 ... its 76' long with 26' T-bars that are about 13' 
from each end. There are massive 3/8" aluminum tubing coils at the center, 
one on either side to add inductance and then I have a 3 relay box for 8 
band segments. With this I have no more than about a 1.8: SWR worse case 
anywhere on the band.

The amp, an Expert 2K then takes that down to no worse than ~1.2:1. Works 
extremely well. I had this in Arizona for about 7 years and now its back up 
at 144' here in South Carolina. (In Arizona it was worse case 1.6:1 across 
the band).

Tom warned me ahead of time it WILL mess with 20 - big time. So I installed 
it turned 90 degrees. What I didn't take in to account when I did the 
modeling of the element relative to the other antennas (which when at 90d 
there is no interaction) was the effect of the T bars! They ended up being 
almost directly above the ends, front and rear, of the 50' boom 5 element 
20 - literally 6' below the T bars. Modeling shows about a 3 db drop in FB 
due to their presence. Modeling shows to remove them I'd need to add 14' to 
the total length - i.e. make it 90' long.

Never been hit - the tower that is with either of these installations (knock 
on wood).

Gary
K9RX

-----Original Message----- 
From: john at kk9a.com
Sent: Monday, October 9, 2017 7:15 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 80 Meter yagi question

Nice antenna Rich! At one time I had a homebrew 90++ foot dipole that
covered the portion of the phone band that I used but on CW the SWR was
pretty high. Are there presets for the tornado coils or do you have to
tune it every time you QSY?

OptiBeam and Force12(sk) use relay controlled coils at the center for
changing resonance.

I wonder how either of these methods hold up to lightning strikes!

John KK9A



To: towertalk at contesting.com
Subject: Re: [TowerTalk] 80 Meter yagi question
From: Richard Thorne <rthorne at rthorne.net>
Date: Sun, 8 Oct 2017 18:58:42 -0500

I can recommend the 80m JK801 rotatable dipole.

I have one at 138' and so far so good.  It's only been up since July so
I'm looking forward to the fall/winter DX season.  The antenna does not
use coils, it uses T-hats towards the ends.  There isn't much droop to
it(note there is no truss cable) and it has handled the winds here in
Amarillo nicely.

There's a picture of my JK stack on my qrz page.  The dipole is at the top
followed by a Mid-Tri Tribander, JK3040SR 40/30 yagi, another Mid-Tri and
finally a F12 WARC 2/2 at about 55' to cover 12/17.  I'll probably add
another Mid-Tri when 10 meters is more active.

The only interaction I've had is on 20m, I had to move the JK801 parallel
with the other booms to fix the 20m swr issue.  At the time of
installation the tornado tuner was not active.  I'm going to climb the
tower and have a buddy monitor the 20m swr while I move the JK801 parallel
with the elements.

Each half of the JK801 is 27' long and with the T-Hat it probably acts as
a half wave on 20m.  I'm hoping with the tornado tuner on line,  that the
20m portion of the upper Mid-Tri won't be affected. I'd like to get this
resolved from an SO2R stand point.  More than likely propagation will be
coming from the same direction on both 40 and 80 which requires both
antennas to be pointed in the same direction vs a 90 degree offset.

I've worked lots of DX on FT8 with it along with some phone and cw.

I can cover the entire 80m band from below 3.5 mhz to above 4.0 mhz via
the tornado tuner and the mfj-1924 controller.

I have the following swr bandwidth as follows:
    - 1.5:1 40 khz
    - 1.75:1 60 khz
    - 2.0:1  80 khz

I use 5 of the MFJ memories to cover cw and 5 for SSB then fine tune if
needed with the up and down buttons.  I may change that to 4 on CW and 6
on SSB.

Rich - N5ZC