On Sat, 13 Mar 2004 12:50:42 -0600, John Fields
wrote:

Again, why don't you post a schematic of what you're up to? Please?-)

The schematic is now on abse....

--

The BBC: Licensed at public expense to spread lies.

Here's the solution. Build a 17.2 one-transistor LC oscillator. It will
easily lock to an injection of the 5th harmonic of 3.44 Mhz at any output
level you like.

Whatever you do don't go for phase locked loops.

Junk your Spice. It tells you nothing you didn't already ought to know. If
you don't know it then you shouldn't be doing the job anyway.

You must have plenty of room on the PCB. But why don't you invest in a 17.2
MHz quartz crystal. They're cheap enough. You've already spent more time
and trouble on research and investigation. Cut your losses.

Redundency is a serious crime. It degrades reliabilty. Reliability is
Quality versus Time. Every individual component must serve a recognisable,
readily understandable purpose. If it's not understood then it shouldn't be
there.

High Quality is adherence to the specified intended purpose.

Now I suppose some bright spark will say deliberate redundency can improve
reliability. But ONLY when all else has failed.
----
Reg.


"Paul Burridge" wrote in message
...
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?

Okay, I've now tweaked the osc. to get as near to 50% as possible.
Alas, still no sign of any 5th present in the multiplier's output.
Here's a shot of the (fundamental) output from the inverters. I can't
see any real problem with why it shouldn't be good for a reasonable
comb of harmonics, but our experts may know better. BTW, settings were
2V/div. and 0.1uS/div.

http://www.burridge8333.fsbusiness.co.uk/trace.gif

This other trace was snapped at the base of the transistor stage that
does the multiplying. All there is (circuitry-wise) between this trace
and the last one is a 330 ohm series resistor and a 47pF cap. I'd have
expected to see some clamping action due to the b/e junction, but the
waveshape seems very odd - but does concur with the Spice simulation.
Is there anything amiss, here? (Setting here is 0.5V/div)

http://www.burridge8333.fsbusiness.co.uk/trace2.gif

Still not a sniff of a fifth! :-(
Currently building Reg's 17.2Mhz BPF to see if that can expose it.
--

The BBC: Licensed at public expense to spread lies.

On Sat, 13 Mar 2004 16:26:10 +0000, Paul Burridge
wrote:


Okay, I've now tweaked the osc. to get as near to 50% as possible.
Alas, still no sign of any 5th present in the multiplier's output.
Here's a shot of the (fundamental) output from the inverters. I can't
see any real problem with why it shouldn't be good for a reasonable
comb of harmonics, but our experts may know better. BTW, settings were
2V/div. and 0.1uS/div.

http://www.burridge8333.fsbusiness.co.uk/trace.gif



That waveform *has* bunches of 5th harmonic. All you need is a
properly functioning bandpass filter to pluck it out.

John

On Sat, 13 Mar 2004 16:26:10 +0000, Paul Burridge
wrote:

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?

Okay, I've now tweaked the osc. to get as near to 50% as possible.
Alas, still no sign of any 5th present in the multiplier's output.
Here's a shot of the (fundamental) output from the inverters. I can't
see any real problem with why it shouldn't be good for a reasonable
comb of harmonics, but our experts may know better. BTW, settings were
2V/div. and 0.1uS/div.

http://www.burridge8333.fsbusiness.co.uk/trace.gif

---
That's close enough to 50% that you should have no problem generating
and extracting a fifth harmonic.
---

This other trace was snapped at the base of the transistor stage that
does the multiplying. All there is (circuitry-wise) between this trace
and the last one is a 330 ohm series resistor and a 47pF cap. I'd have
expected to see some clamping action due to the b/e junction, but the
waveshape seems very odd - but does concur with the Spice simulation.
Is there anything amiss, here? (Setting here is 0.5V/div)

http://www.burridge8333.fsbusiness.co.uk/trace2.gif

---
If you've got the cap and resistor in series with the base, and no other
circuitry in there, then what you're doing is half-wave rectifying the
square wave in the base-to-emitter diode, and that's what you're seeing,
along with what looks like some AC at the fundamental riding on the
falling peaks and rising valleys of the square wave. The reason you
can't see the fifth harmonic is because it's far enough down that
everything else is so much higher in voltage that it's essentially down
in the mud. If you want the fifth out, you'll have to extract it using
a filter of some sort, the easiest being a series tuned trap or a
parallel tuned tank.

Why don't you post your schematic so we can see exactly what you're
doing?
---

Still not a sniff of a fifth! :-(
Currently building Reg's 17.2Mhz BPF to see if that can expose it.

---
That'll probably do it, but it needs to go on the output of the
multiplier, not between the square wave generator and the input, I
think.

Again, why don't you post a schematic of what you're up to? Please?-)

--
John Fields

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?

Okay, I've now tweaked the osc. to get as near to 50% as possible.
Alas, still no sign of any 5th present in the multiplier's output.
Here's a shot of the (fundamental) output from the inverters. I can't
see any real problem with why it shouldn't be good for a reasonable
comb of harmonics, but our experts may know better. BTW, settings were
2V/div. and 0.1uS/div.

http://www.burridge8333.fsbusiness.co.uk/trace.gif

This other trace was snapped at the base of the transistor stage that
does the multiplying. All there is (circuitry-wise) between this trace
and the last one is a 330 ohm series resistor and a 47pF cap. I'd have
expected to see some clamping action due to the b/e junction, but the
waveshape seems very odd - but does concur with the Spice simulation.
Is there anything amiss, here? (Setting here is 0.5V/div)

http://www.burridge8333.fsbusiness.co.uk/trace2.gif

Still not a sniff of a fifth! :-(
Currently building Reg's 17.2Mhz BPF to see if that can expose it.
--

The BBC: Licensed at public expense to spread lies.

In article , Paul Burridge
writes:

Is there some black magic required to get higher order harmonics out
of an oscillator?

[did you miss a class at Hogwarts? :-) ]

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.

As others have suggested, the duty cycle may be off such that
the 5th harmonic is not as strong as it should be (it would be only
about 10% of the fundamental frequency with the 'best' duty cycle).

Part of the problem can be in trying to L-C tune logic gate outputs,
presuming a great deal that such is what you are doing. If you must
use logic gate inverters, use an open collector kind and put a 5th
harmonic parallel-tuned circuit there and couple it to a relatively high
impedance buffer amplifier input. Or, use a transistor stage and tune
the collector (or drain if FET) to the 5th harmonic.

With TTL gates the output characteristics are non-linear in that a
conducting-to-logic-0 state is a rather low impedance source while
output conducting to a logic-1 state is a medium impedance source.
The resulting loading is not good for trying to filter out a 5th or higher
harmonic. An open-collector output allows the average output Z to
be higher with less upset of a tuned circuit.

The above also applies to a series-tuned L-C circuit for the 5th but
that may be an advantage with the curious impedance of TTL gate
inputs. Using CMOS logic gates over all might prove to be an
advantage since their input impedances are quite high and most
output characteristics don't differ as much between logic 0 and 1.

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?

Varactors don't create harmonics all by themselves. Those need to be
"tuned" either through resonant circuits or harmonics selected via
L-C filters. What you want to do can be done with stock parts but in
different arrangements.

Len Anderson
retired (from regular hours) electronic engineer person.

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

"Paul Burridge" wrote in
message ...
Hi all,

I'm only trying to get 17.2Mhz out of a 3.44Mhz source and
am thus far
failing spectrally. I've tried everything I can think of
so far to
no avail.

Any suggestions, please. I'm stumped!
--

The BBC: blah de blah, yawn.

Certainly. Next time you want to put your foot in your mouth
don't remove it from the end of your leg. Then you won't
be.........

Otherwise 17MHz sits in the range of a 74HC4046 PLL. I
shouldn't suggest such things lest you start asking other
questions..... but.

DNA

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?

Are you filtering before amplifying (eg a high impedance 3 pole
bandpass/highpass L-C filter with a gain of about 5 at 17.2MHz).

Does the inverter supply a decent square wave under the load of the filter?

If all else fails, could you reverse the process - generate 17.2MHz and divide
it down to 3.44MHz?

(Many) years ago I made a functional TV modulator for an Apple ][ PC by pulling
out the 3rd harmonic of the 14.318MHz system clock. I know it was only 3rd
harmonic, but it was at ~43MHz, so I would expect similar or better logic should
be able to produce 17.2MHz for you.

On Fri, 12 Mar 2004 13:56:10 +0000, 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!

Tony (remove the "_" to reply by email)