Extracting bitstream from received signal.

The conversion of the demodulated signal (the split-phase signal) into a serial bit stream needs special attention. In the current decoder this is done as follows: This method works fine for strong signals, like HRPT. However, with PDUS the received signal is too weak to get a usable picture.
A few circuits have been tried out to deterimine how to get usable PDUS pictures, using antennas of max. 1.5 m: Both methods give a considerable enhancement. The second one is suitable to build into the FPGA, which minimizes the amount of extra needed hardware.

Results new bit-extractor.

The conversion analog-to-TTL has been improved by means of a LPF filter in the analog part. This simple filter gives already much better results!

The digital integrator has been added to the PDUS decoder. Result: Again a big improvement!


Next pictures show simulation results of the analog and digital integrator.
Result without integrator.
Low noise High noise
Result with analog integrator (in front of decoder)
High noise Very high noise, half period integration Very high noise, full period integration
Result with digital integrator (in FPGA).
No noise Very high noise


For HRPT, the receiver/decoder as-is is good enough to get usable pictures. However, a low pass filter before going to TTL level is easy to add, and will probably give a considerable improvement (usable signal at low elevations and/or smaller antenna).

For PDUS at least the bit-integrator is a 'MUST' to get usable pictures.