According to Fourier, at some mark-space ratios of a square wave certain
harmonics may be missing from the spectrum.

Just generate a a train of very short sharp pulses from the oscillator and
you will find all the harmonics are present allbeit with reducing
amplitudes. A single transistor should do the job.

I read in sci.electronics.design that Reg Edwards
wrote (in
et.com) about 'Extracting the 5th Harmonic', on Fri, 12 Mar 2004:
According to Fourier, at some mark-space ratios of a square wave certain
harmonics may be missing from the spectrum.


For a waveform like this (use Courier font):
_____
/ \ /
_____/ \____________/

with rise-time f, dwell time d, fall time r and period T, the harmonic
magnitudes are given by:

Cn = 2Aav{sinc(n[pi]f/T)}{sinc(n[pi][f+d]/T)}{sinc(n[pi][r-f]/T)},

where sinc(x)= {sin(x)}/x

There seems to be a number of opportunities for a harmonic to 'hide' in
a zero of that function.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

Don't flame, I'm genuinely curious.

Bob

In rec.radio.amateur.homebrew,sci.electronics.design, Bob Stephens
wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

You can google for it (Usenet or Web) and find it, I've seen it
used a good bit in signal processing and such.

Don't flame, I'm genuinely curious.

Bob

-----
http://mindspring.com/~benbradley

In (rec.radio.amateur.homebrew), Ben Bradley wrote:
In rec.radio.amateur.homebrew,sci.electronics.design, Bob Stephens
wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

You can google for it (Usenet or Web) and find it, I've seen it
used a good bit in signal processing and such.

And it shows up in some math classes as well, though its main use is
in electronics. I suspect it showed up because the instructor wanted
to show a real-life example, which just happened to be -- electronics.

--
End-to-end connectivity is the "coin of the realm" for internet
operations. Use it wisely. You only control your end of it.

In (rec.radio.amateur.homebrew), Ben Bradley wrote:
In rec.radio.amateur.homebrew,sci.electronics.design, Bob Stephens
wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

You can google for it (Usenet or Web) and find it, I've seen it
used a good bit in signal processing and such.

And it shows up in some math classes as well, though its main use is
in electronics. I suspect it showed up because the instructor wanted
to show a real-life example, which just happened to be -- electronics.

--
End-to-end connectivity is the "coin of the realm" for internet
operations. Use it wisely. You only control your end of it.

In rec.radio.amateur.homebrew,sci.electronics.design, Bob Stephens
wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

You can google for it (Usenet or Web) and find it, I've seen it
used a good bit in signal processing and such.

Don't flame, I'm genuinely curious.

Bob

-----
http://mindspring.com/~benbradley

On Fri, 12 Mar 2004 16:55:51 +0000, Bob Stephens wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

Don't flame, I'm genuinely curious.

Bob

I see the sinc function all the time. I was introduced to it in school, in
a signal processing class, and people at work use it fairly often. In my
experience it seems that anyone who deals with signal processing or fft's
is familiar with the sinc() function. And I've always heard it pronounced
the same as the word "sink."

--Mac

On Fri, 12 Mar 2004 16:55:51 +0000, Bob Stephens wrote:

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate wrote:

where sinc(x)= {sin(x)}/x

I've never seen this terminology before. Is this standard math parlance or
is it something of your own?

Don't flame, I'm genuinely curious.

Bob

I see the sinc function all the time. I was introduced to it in school, in
a signal processing class, and people at work use it fairly often. In my
experience it seems that anyone who deals with signal processing or fft's
is familiar with the sinc() function. And I've always heard it pronounced
the same as the word "sink."

--Mac

On Fri, 12 Mar 2004 16:08:15 +0000, John Woodgate
wrote:

I read in sci.electronics.design that Reg Edwards
wrote (in
et.com) about 'Extracting the 5th Harmonic', on Fri, 12 Mar 2004:
According to Fourier, at some mark-space ratios of a square wave certain
harmonics may be missing from the spectrum.


For a waveform like this (use Courier font):
_____
/ \ /
_____/ \____________/

with rise-time f, dwell time d, fall time r and period T, the harmonic
magnitudes are given by:

Cn = 2Aav{sinc(n[pi]f/T)}{sinc(n[pi][f+d]/T)}{sinc(n[pi][r-f]/T)},

where sinc(x)= {sin(x)}/x

There seems to be a number of opportunities for a harmonic to 'hide' in
a zero of that function.

Great. So without a spectrum analyser there's no way to tell? If I
examine the output of the multiplier, it's very messy. There's a
dominant 3rd harmonic alright (my frequency counter resolves it
without difficulty) but the scope trace reveals a number of 'ghost
traces' of different frequencies and amplitudes co-incident with the
dominant trace. All rather confusing. I suppose the only answer is to
build Reg's band pass filter and stick it between the inverter output
and the multiplier input? shrug
--

The BBC: Licensed at public expense to spread lies.