Matching (was: Re: [Mobile-Portable] All on list please stand..........)

[D C *Mac* Macdonald]

How about a lumped capacitance instead of
a coil?  In past years with a "bugcatcher"
type of antenna, 910-1000 pFd was in general
usage at the base feedpoint for 75 meters and
470 pFd usually provided a close enough match
for 40 meter usage.

73 - Mac, K2GKK



----Original Message Follows----

All right then...I'll ask two serious on topic questions.

I need to wind a new shunt matching coil (coil placed right across the 
feedpoint) for
my 40M, centerloaded vertical.  At resonance, I measure an "X" of zero ohms, 
an "R"
of 24 ohms, and an SWR very close to 2:1 (where my 706 starts reducing 
output!).
This antenna is about 31 electrical degrees long, so I would expect to see 
something
in the range of 15-20 ohms Z plus (in this case) probably 5-9 ohms ground 
and other
loss. (Anyone please confirm or correct my thinking?)

Now, question 1.  How is the parallel L calculated?  I have just "guessed" 
in the
past and added or subtracted turns until R approached 50 ohms with X 
remaining at 0.
The coil I am using at the moment measures at 7.7 uh.  It is 20 T, #14 AWG, 
1.375 dia
and 10 TPI wound on a "threaded in the lathe" delrin mounting form.  (This 
calculate
correct by anyone?)

Question 2.  Does anyone have one of those old cardboard Shure slide rules 
which
calculate coil data for sale or trade?  I have actual size JPEGs to homebrew 
both the
Shure and the Allied calculators (and will be happy to share), but would 
really like
to have the genuine article.

Thanks Gang, and  Happy Mobiling...

Tom   AA1NZ





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Your Moderator: Dick Flanagan K7VC, mobile-portable-owner at mailman.qth.net