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      G3PLX Project
        G0TJZ system



  G3PLX system

  G0TJZ system

Passive Ionospheric Sounding and Ranging - The G0TJZ System

What you need to use ChirpView

Your computer:

- A PC-compatible running Windows 95/98/NT4/ME/2000/XP, etc. The current release has been developed on Windows 2000 Professional.
- Pentium (or equivalent) CPU running at 100 MHz or more - this represents my best guess based on the software requiring about 33% available CPU power on a 266 MHz Pentium-II. Although it might run on a 100 MHz machine, it may be very prone to losing audio data if you try running other software at the same time.
- 16-bit stereo soundcard with a line input. Note that soundcard microphone inputs are not suitable since they are usually mono even if they have stereo connectors!

Your HF receiver
- USB mode with a normal speech SSB filter (i.e. approx. 3 kHz bandwidth). Wider filters may also be suitable but narrower ones are not!
- Ability to turn off/override the AGC and use a manual “RF gain” control. This is not absolutely essential, but if the AGC is still operating, ChirpView cannot correctly measure signal levels.

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.

In addition

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 mail