If you want to make precise measurements, the frequency accuracy and stability of your receiver must be good. ChirpView receives sounders which sweep at 100 kHz/sec, so a frequency error of just 100 Hz gives a timing error of 1 millisecond.
ChirpView requires an accurate timing reference. The best option is a GPS receiver with a pulse-per-second (PPS) output. You need to connect the GPS receiver’s NMEA data output to one of your computer’s serial ports, and the PPS output to the RIGHT line input of your soundcard (via an appropriate attenuator). ChirpView also supports GPS receivers which do not have a suitable NMEA output and other non-GPS time sources via a “generic pulse-per-second” option. Once again, the pulse-per-second signal must be connected to the soundcard’s RIGHT line input (via an appropriate attenuator). GPS receivers which do not have a PPS output are not suitable! Alternatively, you can use a time signal such as MSF (in the U.K.). For this you need an SSB receiver which can tune to the MSF signal and give (say) a 1 kHz audio tone from the MSF carrier. This should then be fed into the RIGHT line input of your soundcard. Other time signals may also be suitable: they must produce an audio tone which goes off for a short period (say 100 ms) exactly on the start of each UTC second. If you use this option, you will not be able to make high precision measurements using ChirpView. Other options for timing reference may be added in later releases of ChirpView.
|Copyright Andrew Senior, 1999 - 2003|