On Fri, 12 Mar 2004 13:56:10 +0000, Paul Burridge
posted this:

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.

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

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

Jim

In article , (Mike Andrews) wrote:
In (rec.radio.amateur.homebrew),
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. I've tried
passing the osc output through two successive inverter gates to
sharpen it up, but still nothing beyond the third appears after tuned
amplification for the fifth. I no longer have a spectrum analyser so
can't check for the presence of a decent comb of harmonics at the
input to the multiplier stage but can only assume the fifth is well
down in the mush for some reason. I could change the inverters for
schmitt triggers and gain a couple of nS but can't see that making
enough difference. What about sticking a varactor in there somewhere?
Would its non-linearity assist or are they only any good for even
order harmonics?
Any suggestions, please. I'm stumped!

There must be something killing the fifth harmonic, which should be
present at (1/5) of the amplitude of the fundamental in a square
wave. That's a pretty strong component.

If you can amplify the output of the source and then square it up
sharply, the fifth harmonic ought to be pretty easy to extract. The
larger the amplitude of that square wave, the larger the amplitude of
the fifth harmonic, of course, so amplification is your friend here --
but you may want to shield very well indeed to keep other components
out of places where they don't belong and may cause trouble.

Have a look at
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/geowv.html
for a lot of stuff that you probably already know.

Best of luck, and please keep us posted.

Remember the harmonic energy is in the edges of the waveform. You need to
have fast rise and fall times to get the theoretical 1/5 of the fundamental.

From experience an 'ACT type device [74ACT04 or whatever] driving thru a small
resistor [20 to 50 ohms] into a properly tuned tank should work. I have used
that method to due a multiplication to a hifger frequency than you are looking
for.

Dr. G.

In article , (Mike Andrews) wrote:
In (rec.radio.amateur.homebrew),
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. I've tried
passing the osc output through two successive inverter gates to
sharpen it up, but still nothing beyond the third appears after tuned
amplification for the fifth. I no longer have a spectrum analyser so
can't check for the presence of a decent comb of harmonics at the
input to the multiplier stage but can only assume the fifth is well
down in the mush for some reason. I could change the inverters for
schmitt triggers and gain a couple of nS but can't see that making
enough difference. What about sticking a varactor in there somewhere?
Would its non-linearity assist or are they only any good for even
order harmonics?
Any suggestions, please. I'm stumped!

There must be something killing the fifth harmonic, which should be
present at (1/5) of the amplitude of the fundamental in a square
wave. That's a pretty strong component.

If you can amplify the output of the source and then square it up
sharply, the fifth harmonic ought to be pretty easy to extract. The
larger the amplitude of that square wave, the larger the amplitude of
the fifth harmonic, of course, so amplification is your friend here --
but you may want to shield very well indeed to keep other components
out of places where they don't belong and may cause trouble.

Have a look at
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/geowv.html
for a lot of stuff that you probably already know.

Best of luck, and please keep us posted.

Remember the harmonic energy is in the edges of the waveform. You need to
have fast rise and fall times to get the theoretical 1/5 of the fundamental.

From experience an 'ACT type device [74ACT04 or whatever] driving thru a small
resistor [20 to 50 ohms] into a properly tuned tank should work. I have used
that method to due a multiplication to a hifger frequency than you are looking
for.

Dr. G.

On Fri, 12 Mar 2004 20:41:49 +0000, Ian Bell wrote:




Reminds me of the old joke about the mathemetician, the physicist and the
engineer. They were each shown into a room in the centre of which was £50
note / $100 bill (depending on which side of the pond you live).

They were told they could walk half the distance to the money and stop.
Then they could walk half the remaining ditance and so on until they got
the money.

The mathemetician worked out you would never reach the money so he didn't
even try. The physicist, working to five decimal places was still there a
week later. The engineer did three iterations, said 'That's close enough'
and picked up the money.

The moral is of course, horses for courses.

Ian

.......and I always believed John was an engineer, have some similar
expressions which an instructor used the xmas holidays to derive

JM
----
Jan-Martin, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/

On Fri, 12 Mar 2004 20:41:49 +0000, Ian Bell wrote:




Reminds me of the old joke about the mathemetician, the physicist and the
engineer. They were each shown into a room in the centre of which was £50
note / $100 bill (depending on which side of the pond you live).

They were told they could walk half the distance to the money and stop.
Then they could walk half the remaining ditance and so on until they got
the money.

The mathemetician worked out you would never reach the money so he didn't
even try. The physicist, working to five decimal places was still there a
week later. The engineer did three iterations, said 'That's close enough'
and picked up the money.

The moral is of course, horses for courses.

Ian

.......and I always believed John was an engineer, have some similar
expressions which an instructor used the xmas holidays to derive

JM
----
Jan-Martin, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/

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

I read in sci.electronics.design that Tim Wescott
wrote (in .
com) about 'Extracting the 5th Harmonic', on Fri, 12 Mar 2004:

Yes, it's pronounced "sink", and it's quite common in signal processing.
You define it as being the _limit_ of sin(x)/x as x - 0 because
otherwise it's undefined at zero, and all the mathematicians in the
crowd will curse at you for being yet another engineer who's treating
math so casually.

I don't fear the wrath of any mathematician. The limit is very firmly
established as = 1 at a quite elementary level. Just consider the
expansion of sin(x) = x - (x^3)/3! +.....

Of course, it can be established more rigorously, but there is nothing
wrong with the series expansion AFAIK.
--
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

I read in sci.electronics.design that Tim Wescott
wrote (in .
com) about 'Extracting the 5th Harmonic', on Fri, 12 Mar 2004:

Yes, it's pronounced "sink", and it's quite common in signal processing.
You define it as being the _limit_ of sin(x)/x as x - 0 because
otherwise it's undefined at zero, and all the mathematicians in the
crowd will curse at you for being yet another engineer who's treating
math so casually.

I don't fear the wrath of any mathematician. The limit is very firmly
established as = 1 at a quite elementary level. Just consider the
expansion of sin(x) = x - (x^3)/3! +.....

Of course, it can be established more rigorously, but there is nothing
wrong with the series expansion AFAIK.
--
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

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.