Re: Resonator base impedance (help needed)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Subject: Re: Resonator base impedance (help needed)


>Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>
>


Hi folks!

>I'm sure eddy currents and misc. losses will be part of this
>value, but the largest contributor should be the proximity losses.

<lots of snipping>

>>The only text that I'm aware
>> of that covers practical estimation of both skin and proximity effects
>> for single-layer and multi-layer inductors is Terman's excellent 1019pp
>> tome, the "Radio Engineers Handbook, McGraw-Hill, 1943.
>>


Try also the same author's "Radio Engineering" 3rd ed McGraw-Hill 1947 for
other
interesting stuff.

Section 4 (by Gomer L. Davies) in Keith Henney's "The Radio Engineering
Handbook" 3rd ed McGraw-Hill 1941 is worth a look but he doesn't say anything
about proximity effect.

"Reference Data for Radio Engineers" 3rd ed 1949 by Federal Telephone and Radio
Corporation is useful for general info.

"Radio Designer's Handbook" 4th ed 2nd impression with addenda 1954 by F.
Langford Smith (Iliffe, London) has vast amounts on almost everything inside a
radio, including the design of efficient coils, and where he lacks he cites
original papers (like Grover and NBS C74!).

"Radio Data Charts" by R.T. Beatty and J. McG. Sowerby 4th ed 1947 (Iliffe,
London) is a series of ABACS for design of almost anything inside a "wireless"
and includes calculations of optimum wire size, also cites original papers so
you have the references - if you can't find this (and it may be difficult to
get) the relevant ones which deal with skin and proximity effect are by S.
Butterworth, Wireless World December 8th p754 and December 15th p811, 1926.

There are interesting details on the feedpoint impedance of physically short hf
whip aerials (possibly extendable to Tesla secondaries) in older ARRL Antenna
handbooks (I have 1954) and the RSGB Radio Communications Handbook (older
editions in particular - I have the 5th, 1982).  I would also suggest you look
at the Numerical Electromagnetics Code (Fortran 77 rules OK) as a possible
source of modelling info (check out the three manuals for the how, the why, and
the program code listing, as well as the public domain NEC2 code itself):

http://www.qsl-dot-net/wb6tpu/swindex.html
http://dutettq.et.tudelft.nl/~koen/Nec/welcome.html  (no www.)
http://www.cebik-dot-com/

Unfortunately, feedpoint impedance is one thing NEC2 occasionally has
difficulty
with (I wonder why?!  ;-)  NEC is more likely to be interesting than directly
useful, as you will need thousands of segments in the models for a Tesla
secondary and hence a gigabyte or more of memory to run (and a lot of patience
for the results - like hours or days on an Intel/AMD.)  Loaded hf verticals are
however possible. L.B. Cebik's website is particularly helpful.  As the NEC2
code is public domain (God Bless the USA) you might find useful subroutines
which you can utilise in your own program code - there's around 9000 lines
of it
as I recall.

I am currently reading a paper by Prof. C.L. Fortescue, "The Design of
Inductances for High Frequency Circuits" JIEE pp 933-943 (1923) which is as
interesting for the discussion at the end of the paper (some comments by Prof
Howe and Mr Butterworth et al !) as for the techniques of approximation which
Prof Fortescue resorts to.

Well worth it.

My micro-coil (home made induction coil at around 60% efficiency, takes 25W
from
a 12V psu, induction coil secondary around 2lbs of 42swg DSC copper, Tesla
secondary around 1" x 7") has given me some interesting insights.  I stuck a
0-350mA thermocouple ammeter in the earth lead.  With sparking suppressed by a
slightly-too-large topload, the secondary base current was around 200mA (and
this in a 0.1mm/42swg DSC Tesla secondary - yes, it did get warm!) and as
sparks
were drawn to an earthed probe, the base current fell to less than minimum
deflection on the meter - probably less than 20mA.  Looks like impedance
inversion, the drawing of a spark from the topload being roughly akin to
earthing the top of the coil, hence base impedance goes up.  Sparks are
around 2
inches with the optimum topload (1" dia) corresponding to 12-15W of EHT
from the
induction coil.

Just my 12-15 watts worth.  (Been a QRP op since '94).

Dunckx
G0UTY (ex-ON9CHU)