[HBR] Riddle me this!

[Shoppa, Tim]

I hate hate hate the original polysterene forms. They start melting before I ever get a soldering iron near.

I have been having excellent success using 5 pin tube bases from bad 807's and using hollow phenolic tubes slipped inside or over the 5 pin base. I think most PVC (see "microwave test" in case UV resistant additives might cause RF issues) is fine too.

Sent from my Windows Phone
________________________________
From: Brian Burns<mailto:brian at lessonsinlutherie.com>
Sent: ‎11/‎28/‎2014 2:01 PM
To: 'HBR Receiver List'<mailto:hbr at mailman.qth.net>
Subject: [HBR] Riddle me this!

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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