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Spectracom 8170 and Netclock/2 WWVB Receivers
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Spectracom 8170 and Netclock/2 WWVB Receivers
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Address: 127.127.4.<I>u</I>
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<BR>Reference ID: <TT>WWVB</TT>
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<BR>Driver ID: <TT>WWVB_SPEC</TT>
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<BR>Serial Port: <TT>/dev/wwvb<I>u</I></TT>; 9600 baud, 8-bits, no
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<BR>Features: <TT>tty_clk</TT>
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This driver supports all known Spectracom radio and satellite clocks,
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including the Model 8170 and Netclock/2 WWVB Synchronized Clocks and the
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Netclock/GPS GPS Master Clock. The claimed accuracy of the WWVB clocks
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is 100 usec relative to the broadcast signal. These clocks have proven a
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reliable source of time, except in some parts of the country with high
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levels of conducted RF interference. WIth the GPS clock the claimed
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accuracy is 130 ns. However, in most cases the actual accuracy is
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limited by the precision of the timecode and the latencies of the serial
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interface and operating system.
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<P>The DIPswitches on these clocks should be set to 24-hour display,
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AUTO DST off, data format 0 or 2 (see below) and baud rate 9600. If this
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clock is used as the source for the IRIG Audio Decoder
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(<tt>refclock_irig.c</tt> in this distribution), set the DIPswitches for
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AM IRIG output and IRIG format 1 (IRIG B with signature control).
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<P>There are two timecode formats used by these clocks. Format 0, which
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is available with all clocks, and format 2, which is available with all
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clocks except the original (unmodified) Model 8170.
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<P>Format 0 (22 ASCII printing characters):
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<br><cr><lf>i ddd hh:mm:ss TZ=zz<cr><lf>
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<p>on-time = first <cr>
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<br>i = synchronization flag (' ' = in synch, '?' = out synch)
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<br>hh:mm:ss = hours, minutes, seconds</PRE>
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<p>The alarm condition is indicated by other than ' ' at <TT>i</TT>,
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which occurs during initial synchronization and when received signal is
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lost for about ten hours.
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<P>Format 2 (24 ASCII printing characters):
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<br>lt;cr>lf>iqyy ddd hh:mm:ss.fff ld
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<br>i = synchronization flag (' ' = in synch, '?' = out synch)
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<br>q = quality indicator (' ' = locked, 'A'...'D' = unlocked)
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<br>yy = year (as broadcast)
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<br>hh:mm:ss.fff = hours, minutes, seconds, milliseconds</PRE>
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<p>The alarm condition is indicated by other than ' ' at <TT>i</TT>,
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which occurs during initial synchronization and when received signal is
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lost for about ten hours. The unlock condition is indicated by other
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than ' ' at <TT>q</TT>.
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<P>The <TT>q</TT> is normally ' ' when the time error is less than 1 ms
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and a character in the set <TT>A...D</TT> when the time error is less
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than 10, 100, 500 and greater than 500 ms respectively. The <TT>l</TT>
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is normally ' ', but is set to <TT>L</TT> early in the month of an
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upcoming UTC leap second and reset to ' ' on the first day of the
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following month. The <TT>d</TT> is set to <TT>S</TT> for standard time
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<TT>S</TT>, <TT>I</TT> on the day preceding a switch to daylight time,
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<TT>D</TT> for daylight time and <TT>O</TT> on the day preceding a
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switch to standard time. The start bit of the first
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<cr> is synchronized to the indicated time as returned.
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<P>This driver does not need to be told which format is in use - it
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figures out which one from the length of the message. A three-stage
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median filter is used to reduce jitter and provide a dispersion measure.
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The driver makes no attempt to correct for the intrinsic jitter of the
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radio itself, which is a known problem with the older radios.
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The driver writes each timecode as received to the <TT>clockstats</TT>
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file. When enabled by the <TT>flag4</TT> fudge flag, a table of quality
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data maintained internally by the Netclock/2 is retrieved and written to
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the <TT>clockstats</TT> file when the first timecode message of a new
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<H4>Fudge Factors</H4>
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<DT><TT>time1 <I>time</I></TT></DT>
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<DD>Specifies the time offset calibration factor, in seconds and
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with default 0.0.</DD>
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<DT><TT>time2 <I>time</I></TT></DT>
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<DD>Not used by this driver.</DD>
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<DT><TT>stratum <I>number</I></TT></DT>
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<DD>Specifies the driver stratum, in decimal from 0 to 15, with default
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<DT><TT>refid <I>string</I></TT></DT>
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<DD>Specifies the driver reference identifier, an ASCII string from one
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to four characters, with default <TT>WWVB</TT>.</DD>
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<DT><TT>flag1 0 | 1</TT></DT>
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<DD>Not used by this driver.</DD>
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<DT><TT>flag2 0 | 1</TT></DT>
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<DD>Not used by this driver.</DD>
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<DT><TT>flag3 0 | 1</TT></DT>
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<DD>Not used by this driver.</DD>
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<DT><TT>flag4 0 | 1</TT></DT>
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<DD>Enable verbose <TT>clockstats</TT> recording if set.</DD>
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Additional Information
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<P><A HREF="refclock.htm">Reference Clock Drivers</A>
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<HR><ADDRESS>David L. Mills (mills@udel.edu)</ADDRESS></BODY></HTML>
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