[TowerTalk] Exploring another option re interaction 40/15 on

[Jim Thomson]

Date: Fri, 3 Jun 2016 11:15:22 -0400
From: "StellarCAT" <rxdesign at ssvecnet.com>
To: "tower" <towertalk at contesting.com>
Subject: [TowerTalk] Exploring another option re interaction 40/15 on
same tower

Ok ... so the plan is to have 6/6 on 15M at 90/45 and I?m worried about (the unknown) interaction from a 4 el 40 mounted 34? above the top 15. 

One option I have is to simply rotate the 40M 90 degrees and mount it that way. I already have the 80/75 dipole turned that way so the rotor has to have an ?offset? reading capability (Green Heron) ... so why not just ?extend? that to 40 as well. I have a rugged mount that will allow it to be mounted on the 1.5? leg of the Rohn 45 with an arm that goes out to a second leg for added reinforcement ... 

I don?t know if there is an adverse effect between 80 and 40 ? the 80 dipole is ~76? long with hi-Q coils at the center and 26? T bars out 2/3rd of the way to the end... 

There might still be an issue of the boom of the 40, 42? long, interacting with the top 15 but it would be considerably less than the full antenna I?d guess... but only a guess. 

does anyone have any issues with this? I know the wind load is going to be changed to put it lightly ... but with 6 antennas on this tower ? all substantial in size that might actually be a good thing making it less susceptible to the desire to ?point it in to the wind? (for as we all know we can?t always do that). 

thoughts?

Gary 
K9RX

##    Does the entire tower rotate ?   If so, just mount the 40m yagi 90 degs to the pair of 15m yagis below it... problem solved.   The  42 ft boom of the 40m yagi will not screw
up the top 15m yagi..nor the lower 15m yagi.    If your  80m rotary dipole  is  mounted so its  inline with the 40m boom, the 80m  will not affect the  upper /lower 15M.   
The  26 FT long  T bars  on the 80m   will now be  90 deg  from the  15M eles.... which is good.    Those  26 ft T bars will resonate around  18 mhz....which might affect the top 15M array,
but that’s a moot point, since the T bars will be   90 degs to the 15M eles.     ( ditto with the 40M eles...also 90 degs to the 15M eles). 

##  optibeam used 8 x stubs to detune their version of the 4 el 40M.   That plus their coils are not very far out from the boom.     F12 N type  40M eles  use LL rods,  but again,
they are not far out from the boom, only 7 ft 9 inch.  f12 didnt use any decoupling stubs..... however it resonates around 24 mhz... which will screw up a 12m  ant.... but solves the 40 + 15m interaction issue. ( without having to offset the booms  by 90 deg). 

##  If ur sleeve idea works...and shifts the 3rd harmonic resonance up in freq a bunch.....( like way up..as in 24+ mhz)..... then u  wont have to rotate the  40 /15m booms by 90 deg.  

##  If u have a top rotor for the 40 + 80....and side mount rotors for the pair of 15s... then  you might have to rotate the  80/40...but only when operating on 15m.   If ur sleeve ide works good, then u wont have to do that, and
everything can rotate independent of each other. 

Jim   VE7RF