[DSP-10] 10MHz Crystal osc question

Fri, 22 Feb 2002 00:09:37 -0500

Hi Steve,

At the moment, I have C108 at 22pf - Nothing added, C109 is two 10pf SMTs 
in parallel and C110 is the 2.8-12.5pf with a 27pf in parallel as it was 
the most convenient place to put a disk cap for a test without destroying 
SMT caps.

What I probably should do is add to C108 bringing it up to about 32pf and 
reduce the other side so the minimum is about 32pf also. - will give that a 
try tomorrow.

At 09:21 PM 2/21/2002 -0700, you wrote:
>Hello Lee,
>
>The 10 MHz crystal supplied with the TAPR kit should be an Epson CA-301 Type
>(DK SE3420).  There's information about how Bob selected this crystal on the
>DSP-10 web pages.
>
>In looking at the data sheet, the load capacitance is 18 pF.  I assume that
>when you say you are adding 37 pF you are stating the total parallel
>capacitance around the crystal.  If that's the case, then it sounds like you
>are in the ball park.  If C108 is 22 pF and the 37pF you added to C110, in
>parallel that's 13.8 pF.  Add 5 pF for stray capacitance and the total is
>18.8 pF.  So you see, you are there.  Since U104 (LMX1501A) is using a
>Pierce Oscillator, it would be best to balance the load capacitor values.
>
>If I made a bad assumption about your parts placement, can you let us know
>what capacitors you added where?  What values you have for C108, C109 and
>C110?
>
>- Steve, N7HPR
>   ([email protected])
>
>
>
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]]On Behalf Of Lee Scott
> > Sent: Thursday, February 21, 2002 12:02 PM
> > To: [email protected]
> > Subject: [DSP-10] 10MHz Crystal osc question
> >
> >
> > I have my DSP-10 up and running but have had to pad quite a bit on the
> > 10MHz crystal to get it to the right frequency.  As originally
> > constructed,
> > the DSP-10 was transmitting 10KHz high so I padded C109 first with a 5pf,
> > then a 10pf cap.  I was still too high and I had to add a 27pf
> > NPO disk cap
> > from C110 to gnd before the low end of the C110 would tune the
> > osc down low
> > enough to bring it on freq.
> >
> > Am wondering if the 10MHz crystal TAPR is kitting is the right one as I
> > have had to pad a total of 37pf to pull the osc down.
> >
> > Lee Scott - AA1YN
> >
> > _______________________________________________
> > DSP-10 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/dsp-10
>
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