[time-nuts] Spectracom 8170 time clocks simple suggestion

Bob Camp lists at rtty.us
Sun Jun 16 08:50:00 EDT 2013


Hi


On Jun 15, 2013, at 10:38 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> lists at rtty.us said:
>> I think spitting the "bit" out a PC serial port line and running a 74HC
>> series switch would be pretty easy. Less than $10 in parts including the
>> pert board and the time to solder the roughly eight connections.  
> 
> How accurate does the switching have to be?

Any error will show up as a carrier drop out. As long as 90-99% of the carrier is corrected the downstream radio should be ok.

> 
> Note that there are 2 dimensions to the answer.  One is time, how close to 
> the target time does the switching have to occur?

Best guess is that if you transition the switch in  < one cycle at 60 KHz you should be fine. Call it < 15 us if you need a number on it. That's just the transition time. The code alignment would be fine at 1 ms, ok at 10 ms, and messy at 100 ms. 
 
> 
> The other dimension is digital.   What happens if some of the bits are wrong? 
> How many can be wrong before the 8170 won't lock?  There are a dozen bits at 
> the end that I'm not sure I can predict, the DST/Leap/notice stuff.

That's the part that I'd like to see better definition on. I think you can do the DST and leap year bits, it's the data / notice bits that are undefined at this point. 

Bob

> 
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