Fourier (Napoleonic era or earlier?) first used his analysis to study
conduction not of electric current but of of heat. That was long before the
invention of the electric soldering iron. When the soldering iron (actually
copper) arrived Fourier's analysis was already here to greet it.

Then along came Oliver Heaviside who turned the World upside down by
replacing jw with p.

On Fri, 12 Mar 2004 15:32:23 +0000, Ian Bell wrote:

Paul Burridge wrote:

Hi all,

Is there some black magic required to get higher order harmonics out
of an oscillator?
I'm only trying to get 17.2Mhz out of a 3.44Mhz source and am thus far
failing spectacularly. I've tried everything I can think of so far to
no avail. All I can get apart from the fundamental is a strong third
harmonic on 10.32Mhz, regardless of what I tune for.

In RF circles, the 'normal' way to do this would be a simple Class C
amplifier with a collector load tuned to the fifth harmonic. In calls C,
conduction only occurs for a small fraction of a cycle which produces a
correspondingly higher proportion of higher harmonics than a square wave.

I've been waiting for someone to post this. I would only add "The drive level,
and the bais point, will vary the amount of fifth (or whichever) you will see."

It's as common as noses in RF, as Ian pointed out. Just look at the average
two-way radio prior to frequency synthesisers. Crystal freqs were multiplied
this way in transmitter chains and for receive injection, although use of fifth
wasn't especially common because you normally had enough design control to use
the more efficient *2, *3 or *4.

On Fri, 12 Mar 2004 15:32:23 +0000, Ian Bell wrote:

Paul Burridge wrote:

Hi all,

Is there some black magic required to get higher order harmonics out
of an oscillator?
I'm only trying to get 17.2Mhz out of a 3.44Mhz source and am thus far
failing spectacularly. I've tried everything I can think of so far to
no avail. All I can get apart from the fundamental is a strong third
harmonic on 10.32Mhz, regardless of what I tune for.

In RF circles, the 'normal' way to do this would be a simple Class C
amplifier with a collector load tuned to the fifth harmonic. In calls C,
conduction only occurs for a small fraction of a cycle which produces a
correspondingly higher proportion of higher harmonics than a square wave.

I've been waiting for someone to post this. I would only add "The drive level,
and the bais point, will vary the amount of fifth (or whichever) you will see."

It's as common as noses in RF, as Ian pointed out. Just look at the average
two-way radio prior to frequency synthesisers. Crystal freqs were multiplied
this way in transmitter chains and for receive injection, although use of fifth
wasn't especially common because you normally had enough design control to use
the more efficient *2, *3 or *4.

"Reg Edwards" wrote in message
...
The Hyperbolic Cosine is pronounced Cosh.
The Hyperbolic Sine is pronounced Shine.
The Hyperbolic Tangent is pronounced Than with a soft Th.

At least that's the way I've been doing it for the last 55 years.

Have you ever noticed no one sits next to you at meetings?


They don't seem to come up very often in conversation although they are
just
as fundamental in mathematics as are the trigonometrical functions. They
crop up all over the place especially in transmission lines where they
appear in complex form such as Tanh(A+jB).

"Reg Edwards" wrote in message
...
The Hyperbolic Cosine is pronounced Cosh.
The Hyperbolic Sine is pronounced Shine.
The Hyperbolic Tangent is pronounced Than with a soft Th.

At least that's the way I've been doing it for the last 55 years.

Have you ever noticed no one sits next to you at meetings?


They don't seem to come up very often in conversation although they are
just
as fundamental in mathematics as are the trigonometrical functions. They
crop up all over the place especially in transmission lines where they
appear in complex form such as Tanh(A+jB).

Firstly, thanks to everyone who's responded to this question. I've had
plenty of valuable leads to follow up on, for which I am as ever very
grateful.


On Sat, 13 Mar 2004 00:16:28 GMT, James Meyer
wrote:

Is this a simulated circuit or a "real" one built with "real"
components?

It *is* actually a real one in this instance! Although I've simulated
it as well, of course, but that hasn't provided any clues as to what
might be causing the problem with the actual circuit.

I have at least one suggestion, but I need to know whether to send an
LTspice netlist or a gif.

Send 'em both!
--

The BBC: Licensed at public expense to spread lies.

Firstly, thanks to everyone who's responded to this question. I've had
plenty of valuable leads to follow up on, for which I am as ever very
grateful.


On Sat, 13 Mar 2004 00:16:28 GMT, James Meyer
wrote:

Is this a simulated circuit or a "real" one built with "real"
components?

It *is* actually a real one in this instance! Although I've simulated
it as well, of course, but that hasn't provided any clues as to what
might be causing the problem with the actual circuit.

I have at least one suggestion, but I need to know whether to send an
LTspice netlist or a gif.

Send 'em both!
--

The BBC: Licensed at public expense to spread lies.

On Sat, 13 Mar 2004 10:00:52 +1000, Tony wrote:

The 5th harmonic should be only 14dB below the fundamental, although it will
drop fairly quickly as the sides of the input square wave deviate from vertical.

Does the 3.44MHz have a 50% duty cycle?

Not quite, no. Why would that make any difference? I'd have thought
any decent 'squarish wave' of the correct frequency with sharp
rise/fall edges ought to do the trick? It's spewing out the 3rd quite
nicely after all.
How about I post a pic of the sig trace into the multiplier? I'll see
if I can do that a bit later 2day...
--

The BBC: Licensed at public expense to spread lies.

On Sat, 13 Mar 2004 10:00:52 +1000, Tony wrote:

The 5th harmonic should be only 14dB below the fundamental, although it will
drop fairly quickly as the sides of the input square wave deviate from vertical.

Does the 3.44MHz have a 50% duty cycle?

Not quite, no. Why would that make any difference? I'd have thought
any decent 'squarish wave' of the correct frequency with sharp
rise/fall edges ought to do the trick? It's spewing out the 3rd quite
nicely after all.
How about I post a pic of the sig trace into the multiplier? I'll see
if I can do that a bit later 2day...
--

The BBC: Licensed at public expense to spread lies.

On Fri, 12 Mar 2004 15:02:30 -0800, John Larkin
wrote:

On Fri, 12 Mar 2004 16:31:19 -0600, John Fields
wrote:

On Fri, 12 Mar 2004 17:57:24 +0000, Paul Burridge
wrote:


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

---
You may want to try something like this:


COUNTER SCOPE COUNTER
| | |
| | |
FIN--[50R]-+-[1N4148]---+----+-------+---FOUT
| |
[L] [C]
| |
GND----------------------+----+

The 50 ohm resistor is the internal impedance of a function generator,
and when I set it to output a square wave at 1.5VPP, I got 10.8kHz for
the fundamental of the tank. Then I tuned the function generator down
until I got a peak out of the tank, and here's what I found:

Fin Fout Vout fout/fin
kHz kHz VPP
-----|-----|------|---------
10.8 10.8 0.9 1.0
3.58 10.8 0.25 3.02 ~ 3
2.14 10.8 0.2 5.05 ~ 5

So with a square wave in there were no even harmonics and it was easy
to trap the 3rd and 5th harmonics with a tank.


Next, I tried it with a 3VPP sine wave in and got:

Fin Fout Vout fout/fin
kHz kHz VPP
-----|-----|------|---------
10.8 10.8 1.3 1.0
5.39 10.8 0.9 ~ 2.0
2.14 10.8 0.3 5.05 ~ 5

So it looks like the second and the fifth harmonics were there. There
were also some other responses farther down, but I just wanted to see
primarily whether the fifth had enough amplitude to work with, and
apparently it does, so I let the rest of it slide.

So, it looks like if you square up your oscillator's output to 50% duty
cycle you could get the 5th harmonic without too much of a problem. If
you can't, then clip the oscillator's output with a diode or make its
duty cycle less than or greater than 50%, and you ought to be able to
get the 5th that way.

Historical note: about 1960, a guy at HP was doing exactly this with
some new diodes, and he got way more higher harmonics than theory
predicts. To figure it out, they hooked up the just-invented HP185
sampling scope (which then used avalanche transistors to make its
sampling pulses) and discovered the diode reverse-recovery snap
phenom. Soon the scope itself was using this effect. They were
originally called Boff diodes, after the discoverer Frank Boff, but
the name didn't stick (wonder why?) and they became "snap diodes" and
later "step-recovery diodes". I think I may have the HP Journal
article around somewhere.

See page 31:

http://cp.literature.agilent.com/lit...5980-2090E.pdf

---
:-)

--
John Fields