[time-nuts] IRIG-B audio decoder circuits and ICs sought

[Magnus Danielson]

Joe,

On 05/19/2015 03:51 PM, Joseph Gwinn wrote:
> I'm studying up on how IRIG-B decoder circuits work.  What are the good
> approaches, the bad approaches, especially in the presence of noise?
> (I asked on the NTP group, with little result beyond the C/C++ decoder
> software written for the audio channel of a 1990s Sun workstation,
> which it ate alive: 50% cpu load.)
>
> Are there decoder ICs available?
>
> The closest to a decoder IC I've found is some FPGA code from a partner
> of Microsemi (nee Symmetricom):
>
> ..<http://www.microsemi.com/products/fpga-soc/design-resources/partners/semquest>
>
> All marketing and little technical information.  I'll have to find out
> the details.
>
>
> I find very little, though I did find one intriguing idea using a
> Costas Loop to lock to the 1 KHz carrier, and a posting suggesting
> squaring the input signal and phase-locking to the 2 KHz result.  Most
> recent articles on IRIG decoders come from Chinese sources, mostly in
> the AC power industry.

There is a few different approaches for recovering the 1 kHz carrier.
The AM modulation is naturally a bit of a challenge as it will modulate 
the slew-rate.

Once the 100 Hz message is recovered, the break-down is relatively 
straight-forward.

The question is really, what is the requirement you have and what type 
of processing do you think about. A corner of a FPGA will do it.

I prefer the DC level shifted variant of IRIG-B.

Cheers,
Magnus