looking at irig b signal 2

[ski333]

I am checking an irig b signal which in this case is modulated with a 1 khz signal. Being as it is amplitude modulated I would expect a solid 1000 cycle rate to show on the frequency counter. When I measure the signal it ranges from 994 hz to 1002 hz, transitioning back and forth at a regualar rate. Is this normal for irig b ? I have never measured it before with a freq. counter, so I am not sure myself. As it is a 100pps signal, are these pulses keeping it from staying a steady 1khz ?

 

[IRstuff]

IRIG-B also contains data, so you might be seeing the modulation from the encoded data

TTFN

 

[ZapSib]

IRIG get several types of modulation for coding time (from A to .. F? ) . If I remenber well, B is amplitude modulated.

 

[ski333]

Thank you both for your replies. Yes, irig b is modulated with a 1khz sinewave. But it also contains encoded digital data and I am wondering if that data is what makes the freq
counter vary within a range, rather than stay locked at 1 khz solid. I believe the digital data is pulse width modulated giving us the codes for time. I guess the only way I can know for sure is to find another source of irig b
and measure it with the freq counter to see what I get. Not likely to have two bad sources. Personally, I think the problem is elsewhere and a little variance could be normal, but only guessing at this point.

 

[ZapSib]

visit

http://www.hopf.com/manuals/english/pdf_general/irig_serial_time_code_standard.pdf

this document describes how irig works
hope it helps.

 

[richs]

Hiya-

From the IRIG spec 200-04, Appendix C you get the
following for IRIG B

Format B Level (dc)Pulse Rise Time Between 10 & 90%
Amplitude points <= 1 microsecond

Jitter Modulated at Carrier Frequncy <= 1%

Jitter Level (dc) Pulse-to-Pulse <= 1%

Snooping around we find the other following snippets from
Figure 3-1:

"Carrier Phasing - Positive going zero axis crossing of
carrier is coincident with leading edge of modulated
signal"

Carrier Frequency - Carrier Frequencies are an integral
multiple of the modulating signal bit rate. Applicable
carriers are specified for each format."


In answer to your question, no. It is not a function
of the 100pps signal. They are a function of the
modulating signal bit rate (i.e. 100pps).

There you go. As I read it, it's just barely in spec.

Cheers,

Rich S.