[time-nuts] Is there any IRIG-B hardware decoders available?
robert8rpi at yahoo.co.uk
Wed May 15 02:26:34 EDT 2013
You could also download the specification :-)
Sync is a requirement, IRIG STANDARD 200-04 says,
3.2.10 Amplitude Modulated Carrier. A standard sine wave carrier frequency to be amplitude modulated by a time code is synchronized to have positive-going, zero-axis crossings coincident with the leading edges of the modulating code bits. A mark-to-space ratio of 10:3 is standard with a range of 3:1 to 6:1
From: Chris Albertson <albertson.chris at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Tuesday, 14 May 2013, 23:16
Subject: Re: [time-nuts] Is there any IRIG-B hardware decoders available?
THis was not my idea.
I was reacting to the claim that IRIG had to sync the carrier phase.
I had not heard of it before but it was not surprising. And what the
heck, it sounds like a good idea, and a 4046 chip cost about the same
as a 555,
We could "cheat" and actually read the IRIG clock reference driver
source code and see how it works. The NTP ref clock driver reads u-law
sample data at 8096Hz. So it could be 8x sampler the 1KHz carrier, it
could be detecting phase. I don't know.
On Tue, May 14, 2013 at 1:43 PM, paul swed <paulswedb at gmail.com> wrote:
> Boy Chris I don't know what to say here I use IRIG B decoder displays and
> they have been happy with my free running xtal oscillator for 12 years. I
> do not recall IRIG B making phase lock a requirement. I use gps to get a
> time stream then a SXB micro to convert that to IRIG B...
> On Tue, May 14, 2013 at 1:35 PM, Chris Albertson
> <albertson.chris at gmail.com>wrote:
>> OK the 555 timer is not so good of an idea. You need a phase locked
>> 1KHz oscillator.
>> You can also buy IRIG cards for the PCI bus. We used them where I
>> used to work. They are not cheap. Almost any company that working in
>> timing or telemetry will have these cards.
>> But still if the goal is to have the computer's system time track
>> irig, use NTP. It should be easy to build a phase locked 1KHz
>> oscillator. 1K is such a low frequency. I'd thing a 4046 chip would
>> do the job.
>> On Tue, May 14, 2013 at 10:04 AM, Esa Heikkinen <tn1ajb at nic.fi> wrote:
>> > Chris Albertson kirjoitti:
>> >> NTP will so this. There is an IRIG reference clock. You really do
>> >> want to use NTP to discipline the PC's clock. Almost every other
>> >> method is worse and causes time discontinuities.
>> >> If you happen to have TTL level IRIG it s very easy to convert it to
>> >> amplitude modulated IRIG. The standard is a 1KHz tone.
>> >> Build a cheap 1KHz oscillator. A 555 timer is good enough. Then you
>> >> a single transister if IC time switch to modulate the amplitude of the
>> >> signal. The details are not critical.
>> > That's good idea if the phase of the 1 kHz signal is not critical?
>> > I checked the IRIG-B signal with oscilloscope and looks like the 1 kHz
>> > signal's phase is locked to the time signal. The bits will always start
>> > stop at exactly same phase. That makes sense because with phase detector
>> > could be possible to get very accurate timing from the 1 kHz signal -
>> > better than following the amplitude only. That's one reason why I was
>> > interested about chipsets; if they can follow the phase also. I think if
>> > design any hardware for that it should follow the phase also? It may be
>> > complex...
>> > Does anyone know if the soundcard based IRIG decoder will follow the
>> > also, or only the amplitude (?)
>> > --
>> > 73s!
>> > Esa
>> > OH4KJU
>> > _______________________________________________
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>> Chris Albertson
>> Redondo Beach, California
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