[DSP-10] 10MHz Crystal osc question

Thu, 21 Feb 2002 21:21:58 -0700

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
>
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