[TowerTalk] 15 Meter and 40 Meter on the same tower?

[Jim Thomson]

Date: Sun, 02 Jun 2013 11:26:12 -0400
From: Everett Jackson <wz8p at wz8p.com>
To: towertalk at contesting.com
Subject: [TowerTalk] 15 Meter and 40 Meter on the same tower?

I have a 135 ft rotating tower.
I am wanting to put a 5 element 15 meter beam on a 36 ft boom
and a 3 element 40 meter beam on a 46 ftboom on the same tower.

How much space is need between them? Or is this just not a good idea to
start with?

73,
Everett – WZ8P

##  My F-12 340N  ... 3 el – 40m yagi  does not resonate  on 15m.   However it will screw up a 12m yagi. 
So it all depends on the design of the 40m yagi.   F-12 claims  you can put those 40m  N type eles  within 
3 feet of a 20-10m yagi... with no interaction.   I think the N eles  resonate just  above or below the 12m band. 

##  You also have to be careful when 2 yagis are at right angles to each other. 
years ago, folks would try and use a KLM  KT34XA    with a KLM 3 el yagi.... it doesn’t work.  40 + 15m
would interact badly..with both pointed in the same direction.   If one yagi rotated  90 deg, the  40 + 15m  interaction
is now zero,  but a new problem arises.    The 32 foot long boom of the KT-34XA  will screw up 20M band real bad ! 

##  So the Fix  was not to use the 3 el klm 40m yagi on the 32 foot boom,..... but to instead use the klm 4 el  40m yagi on the
42 foot boom.   Then when at right angles, no interaction on any band. 

##  You get those kinds of  problems when using stuff like  tic ring rotors.   with a rotating tower, it is not an issue.
N6BT told me you can get another  kind of effect too..and that’s  when   you mount a physically  larger 40m yagi  above
a  smaller 15m or other band yagi.   It’s a shadowing effect. 

##  In your case,  it’s a tough call.   You might want to put the 40m yagi as high as you can......and then  put the 15m yagi down lower..
a  lot lower.   Like  maybe  a  135 +  80  type of combo.   With 55 feet of separation, it may work. 
If we assume the 40m yagi resonates on 15m.... can’t this interaction be modeled on eznec, etc ???   Put an MFJ on the 40m yagi
or get somebody who has the SAME  40m yagi as you do, to do the test..and sweep the entire HF spectrum... and find out exactly 
where it resonates.   IF it doesn’t resonate  on 15m,   its  gotta resonate some where !!    That also pertains to any ant.  If they don’t
resonate on their 3rd harmonic, they gotta  resonate some where.    

##  Come to think of it, most ants  may well resonate on their 5th   + 7th harmonic as well..but don’t quote me on that. 
My old  quarter wave sloper on 80m  would resonate on 6M ..with a flat swr...go figure. 

Later... Jim   VE7RF