[HBR] Riddle me this!

[Brian Burns]

Hello All,

 

My thoughts have turned to plug-in coils, for no particular reason except
that I'm likely to need a bunch of them if I want to cover all the bands.
Being an inveterate "do-it-myselfer", I'm looking into making my own---you
can see that it's going to be a while before I'm able to listen to 40 meter
CW (;->).

 

So I'm curious about the dielectric properties of the various materials that
I might use for making the forms. I go to good-ol google, and search on
dielectric properties of polypropylene, a likely suspect, and up comes the
following link:

 

http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.h
tm

 

For best selectivity and highest gain we would like our RF amplifier and
mixer plug-ins to be high Q (right?). Air is the best core material to get
the highest Q, but it's a bit deficient in mechanical properties. We need a
form to wind our coils on, and wouldn't it be grand to be able to just order
up some ceramic (probably steatite) coil forms like the old-timers used. So
if Air is the best, and higher numbers are worse:

 

Air............1.000

 

Steatite..........5.3-6.5

 

Bakelite..........3.7

 


Polypropylene.........2.2

 

Douglas Fir...........1.9

 

Wood............1-2

 

Wood!?? You gotta be kidding! Much as I love to work wood, I'll stick to
polypropylene as a more practical material. But, never more will I lust
after ceramic coil forms---or am I missing something here?

 

Cheers,

 

Brian

 

	

 

 



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