[time-nuts] NTP IRIG config help

Russell Rezaian rrezaian at motorola.com
Wed Mar 9 14:45:02 EST 2011

IRIG is sometimes provided as a digital code at something useful for 
directly driving logic (I've seen this intended to drive TTL), and as 
the same digital code amplitude modulating an audio frequency carrier.

The modulated audio is the kind of IRIG that is usually decoded by 
the sound card input decoders.

It's also pretty easy to put on a track on mag tape, which was a very 
common use in days gone past when you could still get mag tape and 
people still used it for instrument data recording.

The demodulated IRIG sounds like the simple digital signal, and I'd 
guess you clock generates something that might be intended to drive 
some sort of digital logic, probably TTL.

I strongly suspect you'll get better results with the "modulated" 
IRIG using the NTP code and a sound card decoder.

At 11:35 AM -0800 2011/03/09, Jim Kusznir wrote:
>It has "Demodulated IRIG" as its main IRIG output, but it does have
>one Modulated IRIG.  Others have told me I want the Modulated IRIG; I
>honestly don't know what the differences are, and I haven't gotten out
>a scope to see.
>On Tue, Mar 8, 2011 at 4:25 AM, Rob Kimberley 
><rk at timing-consultants.com> wrote:
>>  I looked at the data sheet of the sel-2407 and interestingly it states
>>  "demodulated" IRIG-B, which seems a bit odd. Either it's a modulated code
>>  i.e. a sinusoidal wave with amplitude modulation (usually about 3:1), or
>>  it's what we call a DC code i.e pulse width data stream not superimposed on
>>  the 1 KHz carrier.
>>  Rob Kimberley
>>  _______________________________________________
>>  time-nuts mailing list -- time-nuts at febo.com
>>  To unsubscribe, go to 
>>  and follow the instructions there.
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.

More information about the time-nuts mailing list