I'm afraid I don't understand the premise behind this at all. It seems to
me that you are talking about creating a tiny FM transmitter with very
little deviation,and I don't see how that will decrease harmonic content.
The signal with no harmonics is a sine wave at a constant frequency. Doing
ANYTHING to alter this INTRODUCES harmonics. It seems to me that shifting
the osc. frequency will mainly shift the rest of the harmonics with it. I
don't want to take the time to actually try to figure out the result in
full detail,but even if it DOES spread the signal out wider, it won't be by
much, and any unintentional receiver which received the original signal
would probably have enough bandwidth to receive the slightly spread signal,
too.

Sean

At 01:56 AM 6/13/99 +1200, you wrote:
>This MAY be an even better idea than you realise.
>
>There will be some extra noise on Vcc right at the PIC even with good
>decoupling and this will have the result of inducing some noise into
>your oscillator. As a consequence you can expect some random jitter
>on the clock - this in turn will decrease its spectral purity and
>DECREASE the magnitude of harmonics, instead spreading the noise onto
>other frequencies. The end result MAY be to reduce your EMC peak
>emissions slightly.
>
>HP design systems where the clock is deliberately "spread" this way
>for just this reason. Presumably adding varicaps returned to Vcc to
>the PIC clock lines may help this effect :-)
>
>
>regards
>
>
>        Russell McMahon
>
>-----Original Message-----
>From: Ernie Murphy <ernie@SURFREE.COM>
>To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
>Date: Sunday, June 13, 1999 1:43 AM
>Subject: Osc cap return
>
>
>With the PICs I've been using, Vcc not RTN is nearest the oscilator
>pins. I
>don't know if this is true the the whole PIC line, but may well be.
>
>So when I have to ground my osc caps (actually I use a resonator,
>same
>thing applies), I could either go the long way around to the real
>ground
>pin, or "Ground" these caps to Vcc. Guess what I do? Nail em right to
>Vcc.
>
>Vcc is an AC short to ground (what do you think all those bypass caps
>do?),
>and is a fine return point for the caps. My application is an
>accurate
>timer, so I implicitly test start-up time. I've tested these things
>from
>-60 to +150¡C and they start up and start pronto every time.
>
|
| Sean Breheny                   
| Amateur Radio Callsign: KA3YXM 
| Electrical Engineering Student  
\--------------=----------------
Save lives, please look at http://www.all.org
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