[Amps] plate choke

[R.Measures]

On Aug 26, 2005, at 12:48 AM, Alex Eban wrote:

> The main problem stems from the 160 meters operation!
> For the higher bands, chokes are usually in the range of 68 to 100
> microhenries. These are easily wound in a solenoid manner and if you 
> space
> wind the last 20 turns or so, chances are you get a choke without 
> resonances
> in the ham bands. On the other hand for 1.8 MHz operation the coil
> inductance goes up in the millihenry range: a lot of turns, crammed
> together. This is prone to parasitic resonances and usually you will 
> find
> that the better amplifiers DO NOT include the top band, or else, they 
> have
> some queer arrangement, like two chokes in series or some oddly wound 
> choke.
> I remember very well the one made by Barker and Williamson , wound in
> sections, each on of a different number of turns.

I tested this idea by winding two chokes,   One had a continuous 
single-layer, and one had various gaps as per the Handbook.    The 
inductances were about the same and, to my surprise, so were the 
resonances.  This led me to conclude that end-to-end coils do not 
decouple unless the gaps are quite substantial.
--   For maximal decoupling, chokes need to mounted at right-angles.
--   For maximal coupling, chokes need to be mounted end-to-end.  

> At some time Collins used
> them in military radios that covered 2 to 30 MHz continuously. I don't 
> know
> whether someone is making them today. This was on of the main reasons 
> that
> in military equipment (high power!) they dispensed with the choke and 
> moved
> over to series feeding of the high voltage supply. The GRC 106 was one 
> good
> example. It employed series feed of the 2400 VDC supply and took the 
> power
> out through a link on the coil.
> Alex		4Z5KS
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org