[Amps] Plate choke magic?

[Will Matney]

Tom,

Actually, a ferrite core can be used if it's of the correct type of  
material. The material is determined by the frequency that the coil will  
operate at. There a couple of ferrite and iron powder types that would  
work. The reason most are air coils I would think is they are cheaper to  
make. An insulated form is all that's really needed. The air coil formula  
is then used to determine the number of turns for the amount of inductance  
wanted. The higher the frequency, the lesser amount of inductance is  
needed to block the RF, so the choke needs to be designed around the  
lesser frequency that will be encountered. Then you need to make sure the  
choke is not self-resonant at any frequency you wish to operate it on.  
This is done by using a grid dip meter and shorting the coils leads  
together. Any dip at any desired frequency means that the inductance will  
have to be changed slightly to move the resonance point to where it wont  
be encountered. Most of the time this is done by simply adding or  
shortening a few turns of wire. Those staggered windings on some chokes  
are done to stop self-resonance at a particular operating frequency, and  
are really several inductors being connected in series where Ltotal = L1  
+ L2 + L3, etc.. Hope this helps as an explanation.

Will



On Fri, 28 Jan 2005 23:42:10 +0000, Tomm Aldridge <KD7QAE at ARRL.NET> wrote:

> Why are plate chokes seemingly black magic?  Don't you just want a good  
> decoupling of the PS from the Plate; i.e. lots of impedance from DC to  
> Light and no resonances?  How I get that should not be an issue but all  
> teh plate chokes I see are long skinny and sometimes segmented single  
> layer solenoids of questionable wire size.  Why wouldn't a really lossy  
> powdered metal toroid with a few fat turns on it work, assuming the  
> inductance was high enough?
>
> KD7QAE
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