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.
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