[Boatanchors] Resonant Choke Filters (was Please review &

[Dennis DuVall]

Richard, et-al

A brief treatment can be found in the Editors and Engineers "Radio Handbook”  eleventh edition, 1947.  Here a resonating capacitor was added to the choke in a normal pi-secton filter configuration with the capacitor value chosen to resonate the reactor inductance at the supply’s normal operating current value.  No accompaning discussion on why/when this might be a good thing to do.  (Get by with a smaller filter choke maybe?)

My 1941 Radiotron Designers Handbook shows a schematic of a two section choke input filter, the first (input) coke of which has a resonating capacitor.  Again, no accompaning discussion except in the caption which says “Filter in which the first choke is tuned to the fundamental ripple frequency."

Dennis D.  W7QHO
Glendale, CA



> On Jan 6, 2015, at 10:40 AM, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:
> 
>   One of the few places I've seen a reference to the use of a resonant input choke for regulation is in _Single Sideband Principles and Practices_ Pappanfus, Bruene, Schoenike  (1964) McGraw-Hill Book Co.  See p.224  Chapter 15 is a discussion of power supplies for SSB transmitters. The authors are all Collins engineers although Pappenfus had left at the time of publication.
>   Some classic engineering books have been mentioned in this thread. I looked at the _Radiotron Designer's Handbook_ 4th edition but could find nothing on the use of a resonated choke. The Radiotron book is aimed mainly at receiver and relatively low power audio amplifiers rather than transmitting equipment. I also looked at _Radio Engineering_ 3rd edition, F.E.Terman, he has a good section on power supplies and various types of filters but nothing on resonated chokes. _Reference Data for Radio Engineers_ 4th edition, has a good section on power supply configuration and how to calculate ripple and regulation of conventional filters but has nothing about resonated chokes. It does mention swinging chokes another subject that is rare in engineering books but _is_ covered in older editions of the ARRL and Radio handbooks.
>   I began to research this some time ago when someone from a country with fifty Hz current wrote about the voltages in his Collins amplifier being off the handbook values. This amp has a resonated choke so the ripple frequency is very important. The cure was to change the value of the capacitor to compensate.
>   Note that this is all based on the fact that the effective inductance of an iron core inductor varies with the current going through it.  Usually power supply chokes are marked for value at a specified amount of current. If one measures such a choke on an impedance bridge with just AC the value will generally be quite a bit higher. However the inducatance may also vary with the level of AC so getting meaningful measurements needs some understanding and care.
> 
> 
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com 
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