[time-nuts] Cheap 9.8Mhz Sa.22c's

[Jim Lux]

On 6/2/13 12:52 PM, WB6BNQ wrote:
> Hello Mark and crowd,
>
> I own one of these and I can guarantee that it CANNOT be moved without changing the crystal, tweaking a
> micro-minature coil value, and changing the firmware.  And NO !, the company would NOT send out the firmware
> needed.  However, if you wanted to spend between $500 and $1000 they would fix it for you.
>
> While there is a DDS inside, it and the crystal are part of Rubidium frequency locking loop.  The actual output
> frequency is generated by dividers in a big ASIC/FPGA/whatever device.  YES, that output frequency is derived from
> the crystal frequency.
>
> They start by choosing a output frequency which selects the crystal frequency.  The crystal is multiplied up to some
> frequency and mixed with the output of a DDS (also driven by the crystal) to produce the final frequency multiplied
> further to get to the Rubidium resonance.  So, without a change in the firmware, there is no way to tweak the unit
> more than a very small amount.
>
> BUT all is not lost.  The 9.8304 MHz frequency is related to the common RS-232 modem frequencies.  It is also
> related to the common sound card frequency of 24.576 MHz.  There it is possible to phase lock it to 10 MHz.
>

You mean bit clock, not modem, I think.. 9.8304 M = 512 * 19.2 k  so you 
can make all those baud rates down to 300 baud/sec. I don't think you 
can get 110 bps, but you could even Rb lock your old ASR33 by dividing 
down to 60 Hz (it evenly divides to that) and running the synchronous 
motor off that.

That 24.576M sound card is at 2.5x