# Re: Racing Spark Prediction

```Original poster: dest <dest@xxxxxxxxxxxxx>

Hallo Gerry.

> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

> I too believe they dont modulate, but when you say:

>>But a beat waveform can also be considered to be a sin wave
>>amplitude modulated by an other sin wave ie sinA+sinB = SinA * sinB

above is incorrect, what Bob wrote before -
sinA* sinB = sin(A-B) + sin(A+B) is incorrect too,
correct formula - sinA + sinB = 2sin[(A+B)/2]cos[(A-B)/2]

>>> I believe, when the two sin waves "add" there is not the upper and
> lower side bands that occur when the two sin waves multiply.

f1=60khz, f2=66khz, a=sin(w1t)+sin(w2t), fourier analysis of a:

http://himplast.ru/dest/temp/gr1.gif

> In the "added" case, there is a beat frequency associated with A-B
> that goes up (and the period goes down) when the coupling is increased.

when coupling is increased the period is going up so beat frequency is
going down.

> Hi Dest,   (is that better?)

sure, but why use capitals? i`m not from some sort of doctors : )
don`t know how, but Terry always beat all of you guys, probably he
uses one of his "secret weapons" again % )

> I believe both the primary and secondary have both frequencies in
> them.  Its not a case where the secondary takes on one frequency and
> the primary takes on the other.

you didn`t understand me - i was trying to say, that secondary gets
new resonance frequency Fupper, and that actual working frequency when
two tanks are coupled and resonating is not higher than Fupper, two
maximum in spectrum is not higher than Fupper too, so you can`t get
voltage maximum below the toroid and overvolt the secondary.

> If both frequencies are in the
> secondary and a "full" beat period occurs (and lets say there is no
> decay in this period of time) then the beat envelope could aggrevate
> the voltage gradient to cause a racing arc.  That's the premise this
> discussion is based upon.

sorry, don`t understand - why doesn`t this envelope cause racing in
the first half of the beat?

```