[Boatanchors] Resonant Choke Filters (was Please review &

[Richard Knoppow]

    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