[TowerTalk] TowerTalk Digest, Vol 129, Issue 14-0- Resonant freq of dipole vs height

[Pfizenmayer]

Here are some numbers to entertain your self with - this is for a linear 
loaded M2 40M1L dipole so the change may be a bit more than on a full size 
dipole and the inv vee will make things different .


Starting from resonance at 6 feet above AZ ground where I cannot even stick 
a shovel in the ground .
( I have in the past measured a ten meter dipole at heights from 3 to 18 
feet above ground and then tried
back into the ground constants using  EZNEC but do not believe the numbers 
are valid)

6 feet -- 7015
26 feet - 7080
factory 50 feet - 7250

or looking at it another way - at 50 feet and 8 feet above a KT34 boom

45.5 inch tips

6 feet - 6922
26 feet -6995
50 feet as above (over KT34) - 7090
50 feet factory numbers - 7145

Incidentally I did the 6 and 26 foot resonances from 39 to 49 inch tips 
(7032 to 6868)
and the two plots of res freq  vs tip length  vs height stay 35 - 36 khz per 
tip length inch apart  .

The 26 feet to 50 feet factory numbers are about 145 khz apart and the 
factory slope
is a tad higher - runs 135 to 170 khz /inch tip length .

At $35 per tip inch length change crane time , I was not interested in 
generating
 my 50 foot curve  , I just set it at 7090 and its under 1.5:1 from 7000 to 
7190
which is what I was after for cw end of band with some SSB and no tuner.

All using a K9YC type 5 turn 6 core (#31   2.4 inch) of RG213 choke  at 
feedpoint .
(And he is not kidding about spreading turns - its HUGE for this choke )

FWIW -- as an aside - M2 adds a little "stinger" at the inboard side start 
of
the linear loading to give a 17 M  resonance - that looked great on 
ground -(but way low in freq )
at  26 feet still good swr but still low in freq -

At  50 feet and 8 feet above the KT34 (element parallel to the KT34 boom) it 
does not even
vaguely look like anything  at 6 or 26 feet anywhere around  17 meters --- A 
very rough
EZNEC model of the KT34 shows a boom resonance about 18 mhz with the 
parasitic
elements floating thru about 15 pfd (SWAG) . Sure wish I could reach ends of 
boom
to hang on a stinger or ground the elements to the boom  to confirm that 
boom resonance.