Checking the GPS 1PPS signal

The -d option enables the output of the 1 PPS status information. Connect the GPS 1 PPS signal to one channel of the sound card. If necessary, use the -p option to specify the channel number.

[james@localhost UltraMSK-1.0b1]$ ./msk -f 19800 -d
% Your evaluation license will expire on 2006-08-31.
% Connected to VLF signal on input alsa_pcm:capture_2
% Connected to PPS signal on input alsa_pcm:capture_1
1152004946.009 95990.332981 -0.000100698 1 -0.999998
1152004947.009 95990.202865 1.69984e-06 1 -0.999995
1152004948.014 95990.229544 2.78753e-06 1 -0.999998
1152004949.009 95990.253993 4.58451e-06 1 -1.000000
1152004950.008 95990.275939 5.89242e-06 1 -0.999995
1152004951.012 95990.294966 6.60543e-06 1 -0.999998
% Terminating...
[james@localhost UltraMSK-1.0b1]$

Terminate using Ctrl-C. For each GPS pulse received the program outputs one line of 5 numbers. The first number is the unix time stamp of the pulse. The second number is the current estimate of sound card sampling rate. The third number is the time difference between an internally generated 1 Hz signal and the received GPS 1PPS signal. The fourth number is the number of seconds since the previous GPS pulse was received. The fifth number is the correlation coefficient of a linear fit to the phase of the GPS pulse versus frequency. This value must be very close or equal to -1.0.

Check that 1 line of numbers is output each second. UltraMSK will not function if the GPS 1 PPS signal is not correctly received. UltraMSK assumes that the rising edge of the GPS pulse is synchronized to UTC. If not then you will need to use the -g option to invert the 1 PPS signal.