Fwd: RE: [DSP-10] 10MHz Crystal osc question

Fri, 22 Feb 2002 14:19:11 -0500

>
>         I can say for sure I had to parallel somewhere near 15-20 pf on 
> each leg of the oscillator to get mine going. I will check and see what 
> it was . I have not built the second one yet, but will be interested to 
> see what it needs. Doug KB8GVQ
>


>At 12:42 PM 2/22/02 -0600, you wrote:
>>STEVE:
>>  >If C108 is 22 Pf and the 37 Pf you added to C110, in parallel that's 13.8
>>Pf.
>>
>>If the capacitors are in parallel, the values need to be added, if the
>>capacitors are in series the capacitors need to be added with the inverse
>>value and the result the inverse value.
>>
>>  59 Pf if in parallel  or 1/22 + 1/37 = 13.79 Pf if in series,.
>>
>>Regards
>>
>>Nando
>>
>>-----Original Message-----
>>From: [email protected]
>>[mailto:[email protected]]On Behalf Of Steven Bible
>>Sent: Thursday, February 21, 2002 10:22 PM
>>To: [email protected]
>>Subject: RE: [DSP-10] 10MHz Crystal osc question
>>
>>
>>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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