lists at rtty.us
Fri Aug 31 22:16:16 EDT 2012
Ok, that gets you back to the basics of really major delta F / delta T slopes.
On Aug 31, 2012, at 8:55 PM, Jim Lux <jimlux at earthlink.net> wrote:
> On 8/31/12 7:06 AM, Bob Camp wrote:
>> An SC is going to have it's temperature curve centered up around 95C
>> or so. If it's been cut as an OCXO crystal the turns will be up there
>> as well. By the time it gets to room temp, the delta F / delta T is
>> moving mighty fast. Think in terms of multiple ppm/C. A typical cell
>> phone TCXO crystal is in the sub 0.1 ppm/C range in the vicinity of
>> room temp. In addition, SC's are pretty hard to pull. For a normal
>> TCXO (no DDS) something > 40 ppm of range would be needed. By the
>> time you get the wide tune stuff in the circuit, the phase noise
>> isn't going to be anything special.
> We're not pulling the crystal.. we just let it sit.
> What we do is change an NCO in the software radio implementation. Typically, you have a coarse tune with a PLL in steps of 500kHz-1MHz, and then you do the fine tune in software with a digital mixer/downconverter and an NCO (which also is part of the carrier tracking loop).
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