[TowerTalk] Ferrite Cores in Trapped Dipoles

[David Gilbert]

There's an old DOS program called "Coil.exe" that calculates inductance 
and self-resonance (both parallel and series) for single layer 
cylindrical air-wound coils.  I have no idea how accurate it is for 
calculating resonance, but it seems to be pretty close for inductance 
for simple coils.  At least I would think it should get you in the 
ballpark for building a trap.  The program is freeware and runs fine on 
my Windows XP machine, and at least one of the sites where you can find 
it is here:

http://www.rfcascade.com/index1.html

Click on "circuit design" at the left, then scroll down to find the program.

Caveat emptor ....

Dave  AB7E




Bill Turner wrote:
> ORIGINAL MESSAGE:
>
> On Tue, 6 Feb 2007 19:10:58 -0500, "Dan Zimmerman N3OX"
>  <n3ox at n3ox.net> wrote:
>
>   
>> Yet many of us are using autotuners (which all have powdered iron
>> inductors) on pathological matching cases, probably with high
>> circulating currents.
>>     
>
> ------------ REPLY FOLLOWS ------------
>
> Yes, it can be done but doing it right requires some careful
> engineering. It's not something you want to slap together in a couple
> of minutes and put up in the air.
>
> I still maintain that the best traps (i.e. lowest loss and most
> reliable) have cores made of nothing but air. Also, the only
> capacitance present should be the self-capacitance present between
> turns of the coil. A trap like this is a bit harder to make because it
> requires considerable cut and try trimming to achieve resonance, but
> once made, will work without problems for years on end.
>
> Bill, W6WRT
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