IRIG-B decoding

The recent F/V conversion with an ADC question got me to thinking about an IRIG-B decoder about which I once speculated. For those not familiar with IRIG-B, the demodulated signal is 1 KHz with groups of five cycles at a peak voltage to indicate a binary one and five cycles of 1/2 peak voltage to indicate a binary zero. It seemed as if almost any ADC could be used to have an adaptive decoder that could handle variations in the peak voltage. The only complication I could see at the time was the difficulty of detecting the peaks without some sort of zero-crossing detector.

Would it be feasible to sample at say 4 KHz and adjust the time window until the sampling is synched to the signal? You'd slide the window until getting near zero readings on alternate samples?

Reply to
Everett M. Greene
Loading thread data ...

The IRIG decode would probably be pretty do-able with an 8 bit microcontroller because the signal is a 1KHz AM signal. The other post was talking about 480KHz FM which would require a good bit more sampling speed and computational speed and complexity.

You don't say what the amplitude of the signal is, but assuming that it is at least 2.8VPP, I think I would try AC coupling the signal and then feeding it into a rectifier bridge. The negative output of the bridge would be grounded and a simple RC filter with a time constant around 3 milliSeconds on the + output of the bridge. The filtered output could be fed into the A/D and the thresholding could be handled in firmware, or if the amplitude of the signal is stable and specified, you could probably use a simple analog comparator with a resistive divider to supply the threshold voltage. If the A/D approach were used, the sample rate and computational load for decoding the signal would be a good bit lower than the firmware PLL that you had described. Either way, it sounds pretty easy.

Good Luck, Bob

Reply to
MetalHead

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.