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Re: PC board primaries
Original poster: "R Heidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
on 12/10/01 5:25 PM, Tesla list at tesla-at-pupman-dot-com wrote:
> Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi Robert,
> On 10 Dec 2001, at 11:54, Tesla list wrote:
>> Original poster: "R Heidlebaugh by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
>> on 12/10/01 8:09 AM, Tesla list at tesla-at-pupman-dot-com wrote:
>>> Original poster: "Barton B. Anderson by way of Terry Fritz
>>> <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>
>>> Hi All -
>>> An idea (not sure if it's been thought of - I haven't paid close
>>> For a double-sided pc board, the top and bottom trace can be slightly
>>> overlapped. This would make it possible to simply etch/cut simple circlular
>>> traces (a gap must be cut between each circle to prevent a shorted turn). A
>>> feed through between upper and lower circle traces can link each turn.
>>> Something like this: You have to use your imagination a little.
>>> 1 3 5 7 9
>>> ---- ---- ---- ---- ----
>>> | | | | | | | |
>>> ---- ---- ---- ----
>>> 2 4 6 8
>>> Space saving as well considering this approach:
>>> 1 2 3 4 5 6 7 8 9
>>> ---- ---- ---- ---- ---- ---- ---- ---- ----
>>> Anyway, I was just thinking about the ease of simple circles instead of a
>>> continuously growing traces.
>> AS I REPLIED BEFORE,PC board coils are subject to high frequency harminics
>> and require neutralizing to avoid TVI.
> Could you explain that answer in more detail please? How much
> difference is there between an air insulated spiral and one sitting
> on copper/fibreglass laminate at TC frequencies? And how would you go
> about neutralizing such a coil?
> Single sided coils work well and also
>> double sided coils with each winding overlaping each other. Winding to
>> winding capacitance is high with double sided coils and must be corrected
>> for. Single sided coils have extreamly low capacitance, and must be
>> compensated for at the other extream.
> Again, how would one compensate? I would have thought that turn-turn
> capacitances were insignificant compared with the primary capacitance.
> Coils are made with helical winding
>> spirals or circular turns steped out to the next outer wind at each loop
>> end. Both work. square box coils work, but harmonics are an even greater
>> problem with lower "Q" coils. Edge emmisiom is no problem as suggested by
>> another TC fan. Make shure your winding to winding spacing is sufficent.
>> Standard 60 mill glass board will hold the output of a 15KV NST with no
>> problem, but keep at least 1 in from the board edge.
>> Robert H
A circuit board acts as a strip-line circuit which can and will produce
harmonics easly over 2 GHz. Low value ceramic or mica capacitors at the
terminal points of the copper runs will prevent self oscilation of the runs.
High value resistors will also reduce the circuit Q and stop oscilation. A
wire coil has a large wind to wind capacitance that dampens oscilations
along the turn to turn length of the winding preventing standing wave high
frequency oscilations. A circuit board has nearly no winding to winding
capacitance, but has high inductance and no resistance to dampin the Q along
the runs so standing wave oscilations pop up along the runs. THE LACK OF
turn to turn capacitance makes the resinant frequency of the natural coil
high. When a two sided board coil is used just the opposite happens. The
capacitance through the board is very high, much higher than air between
coil windings of an ordinary coil so the natural double coil frequency is
much lower than a free air coil. The results is much lower external
capacitance is neaded.I hope this helps. I have used PC board coils and
strip line resonant circuits. The trial and error time is fun, but quite
rewarding when you are done. I use copper tape to make my lay-out board and
do my testing before I etch my final board. This saves a lot of trial and
error cost. Copper tape is available at glass shops and larger hobby shops
that cater to stained glass hobbyists.