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Re: Oil-immersed RFCs


From: 	Mark S Graalman[SMTP:wb8jkr-at-juno-dot-com]
Sent: 	Wednesday, September 03, 1997 4:38 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Oil-immersed RFCs


    Hi Owen,  The reason RF chokes are wound in sections is to reduce the
distributed "C" in the winding, in
transmitter plate circuitry this is important because if the choke
becomes self resonant at the frequency the
transmitter is being used it will absorb power and self destruct. In
tesla coil applications this is not really
an issue, but voltage break down is and by winding the choke into
seperate sections you in effect are 
creating several chokes in series and the RF voltage will divide between
the sections. You could picture
it as resistors in series.

				Mark Graalman



Mark Graalman,   Toledo, Ohio
Callsign: WB8JKR
Member: Society of Telecommunications Engineers
Member: ARRL
Member: TCBA


On Tue, 2 Sep 1997 22:20:35 -0500 Tesla List <tesla-at-pupman-dot-com> writes:
>
>From: 	Owen Lawrence[SMTP:owen-at-iosphere-dot-net]
>Sent: 	Tuesday, September 02, 1997 9:21 PM
>To: 	Tesla List
>Subject: 	Re: Oil-immersed RFCs
>
>> From: 	Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
>> Sent: 	Monday, September 01, 1997 5:02 PM
>> To: 	Tesla List
>> Subject: 	Re: Oil-immersed RFCs
>(snip)
>> You are correct. The reason for many sets of windings is MORE to
>> insure adequate breakdown voltage protection than to gain
>> inductance... although you obviously get BOTH. If you increase the
>> width of each section you increase the number of turns and thus the
>> inductance of each section, but the voltage rating of that section
>> will then DECREASE. 
>
>Here's a quote from the Radio Amateur's Handbook:
>
>   "Many of the popular sizes of RF chokes consist of a number of 
>small,
>flat sections of wire, called pies, separated about an eighth of an 
>inch on
>a ceramic form.  The wire itself is wound in a honey-comb pattern, so 
>that
>the turns are slightly separated.  The purpose of both spacings is to
>minimize the capacitance action between adjacent wires and groups of 
>wires.
> This must be taken into consideration because it has the unwanted 
>effect
>of turning the choke into a resonant circuit all by itself or of 
>nullifying
>its choking action by providing a low-impedance path of its own to the 
>very
>RF currents the choke is supposed to block off."
>
>No doubt this was meant to apply to lower voltages, but it still 
>suggests
>that there are other reasons chokes have the geometry that they do.  
>I'm
>just mentioning this (out of my own ignorance) because this is the 
>first
>time that I ever heard that having many sets of windings is for 
>increasing
>breakdown voltage protection.  Comments?
>
>  - Owen -
>
>
>
>