How ASI and 310M Clock Can Be Improved

Overheard in the lab, "Our clock improvement mechanism is seeing great success out in the field.  One broadcaster had recently installed a new transmitter.  His old ASI to SMPTE 310 converter had such sloppy frequency accuracy that his new exciter would not lock to it.  This can be a big challenge because the SMPTE spec is very loose – too loose, in fact.  It allows a frequency error of up to 2.8 ppm.  This corresponds to the 'old-school' subcarrier frequency spec of 3.58 Mhz +/- 10 Hz. 
That much frequency error corresponds to a bitrate offset of 54 bps (bits-per-second) for the 19.3 Mb/s ATSC service.  The new transmitter  was only sped'd to tolerate a maximum bit error rate of 20 bps.  This is, I believe, a case where the transmitter manufacturer was forced to a much tighter spec than the standard called for in order to produce an acceptable output."

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