I have just posted a new (and experimental) version (3.32) of SHOWTIME on
aleph in the file

   ftp://aleph.gsfc.nasa.gov/GPS/totally.accurate.clock/shwtm332.zip

This ZIPped file is not a complete distribution image -- unzip it to produce
the file shwtm332.exe which you can use to replace your existing showtime.exe.

Aside from some minor maintenance fixes (documented in showtime.hst in the
ZIP file), v3.32 was produced to add a new capability we needed for some of
our R&D programs. We often use the TAC as the equivalent of a "GPS OhmMeter"
for testing antennas. We wanted to be able to generate SNR vs AZ/EL data for
several tests we are doing. SHOWTIME v3.32 adds a new data logging capability
to the [_]Data Logging switch.

Formerly [_] was a two position switch, turning on/off a log of all the NMEA
messages from the receiver. The data is logged to a file named SHOWTIME.LOG
and looks like this:

$GPGGA,055110.00,3911.314,N,07656.137,W,1,05,1.7,99.7,M,-34.0,M,,*6B
$GPGSA,A,3,18,03,19,,31,29,,,,,,,3.3,1.7,2.9*34
$GPGSV,2,1,08,03,54,057,32,18,43,231,24,19,51,310,29,22,22,070,*79
$GPGSV,2,2,08,27,15,308,,28,09,041,,29,18,184,15,31,72,171,27*73
$GPZDA,055110.00,12,09,1996,00,00*6B

with 4-6 (depending on the number of GSV messages) lines of data per second.

The new logging capability makes [_] into a 3-position switch generating
comma-separated (CSV) logs at a rate of one line per minute (logged at 00 
seconds) looking like:

.24444, 8,99.9, 1.9,99.9, +31,73,170,27,  +3,54, 57,30, +19,51,310,27, +18,43,231,26, -22,22, 70, 0, -29,17,184, 0, -27,15,308, 0, -28, 9, 41, 0
.24514, 8, 2.8, 1.9, 2.1, +31,73,169,26,  +3,53, 56,30, +19,51,309,28, +18,42,230,26, +28, 9, 41,13, -22,21, 70, 0, -29,17,184, 0, -27,16,308, 0
  etcetera


The data in the two sample lines have the following CSV format:

.ddddd,##,PDOP,HDOP,VDOP, PRN,EL, AZ,SNR,PRN,EL, AZ,SNR,.... PRN,EL, AZ,SNR,.... PRN,EL, AZ,SNR
.24444, 8,99.9, 1.9,99.9, +31,73,170,27,  +3,54, 57,30, .... -28, 9, 41, 0 <cr><lf>
.24514, 8, 2.8, 1.9, 2.1, +31,73,169,26,  +3,53, 56,30, .... +28, 9, 41,13, .... -27,16,308, 0 <cr><lf>

where .ddddd = time in fractions of a day (at hh:mm:00)
          ## = Number of satellites visible (above elevation mask)
        xDOP = 99.9 if xDOP is not applicable

There are 4 entries for each visible satellite in elevation order. The +sign
on the PRN means that the satellite is locked and the SNR is in the same 
(approximate) dB units as shown on the SHOWTIME screen. A negative PRN and
SNR=0 means that the satellite was not in lock at the time the log entry
was generated.

In the example above, the first line with PDOP=VDOP=99.9 indicates that the 
receiver was only generating a 2-D solution at that PRN28 was not in lock
at 9 degrees elevation. One minute later the receiver had achieved lock on
PRN28 and was able to generate a 3-D position fix.

CSV format was chosen for easy import into spreadsheet programs (like EXCEL
or QUATTRO). This also dictated the use of a fraction-of-day time stamp. The
line length is variable (5 + 4*## entries) since the ## of satellites in
view varies.

Since [_] is a 3-position switch and since the NMEA data logging position
is hit before the CSV position, your log will begin with a few lines of
NMEA data. You may need to manually edit the log to remove these lines,
depending on the flexibility of your spreadsheet's CSV data input. I find
these NMEA entries at the top of a log to be useful because they provide
a date/time stamp of the log.

The "official" release date for v3.32 is Friday the 13th. This follows a
long tradition of releases on dates like April 1, July 4, December 25th, etc.

Tom Clark