AHAAAAAAA ___ I just put up a Msquared 40M1L with the 17 meter "stinger"
about 8 feet above a KT34 - on the ground and at 26 feet on my roof -
everything looked normal (usual shift lower in freq close to ground ) - but
when I put it up at 50 feet ( in line with the KT34 boom since my old 40M
rotary dipole screwqed up the KT34 F/B on 15 meters badly), 17 meters
became almost 2:1 and the SWR curve looked totally different from on the
ground - was now about 1.8:1 from almost 17 mhz to 18350 !!!! . Before it
had the typical SWR dip. (all measurements with VNA2180). While the crane
was here , I started clipping off ends of the stingers and not much was
happening , on the roof it followed the lengths as it should have. I quit
because it was not moving appreciably and it was about $35crane time per
clip . 40M followed factory dmensions closely .
Msquared says they have no data , not even a freq sweep at height by
itself.
I did a simple EZNEC model of a 16 foot long 3 inch diameter boom with 15
foot elements at end and depending on how much capacitance (about 15 pfd and
less) you put from the element center to the boom , you can move the boom
resonance from around 15 mhz to about 19 mhz . So I suspected that was what
was happening -- but all I got was a ten yard stare from M2 . (When I was
working on the KT34 15 meter F/B , I ran hundreds of patterns with a source
a mile away and looking at front to side - , F/S was a tad better on 20 and
15 with the ref and dir floating so I left it that way. Next time a crane
is here I think I will put the straps on to connect the KT34 ref and dir to
the boom and see what happens to 17M.
BTW the old 40 M KLM rotary dipole was 35 feet above and about 10 feet
horizontally away from the KT34 while I was working on it , and it would
move 15 M F/B from 19 dB to 6 dB or so and at different freq for best F/B as
I rotated the dipole broadside or at end on to the signal source . I chased
that one for several days until it dawned on me I was leaving the dipole at
various positions as I tried to set the KT34 reflector resonances. I did
not expect that much interaction at 35 feet away .
Sounds familiar -- Thanks VE7RF .
73 Hank K7HP
## 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.
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