Multi-stage equalisation method and apparatus for use in telemetry

A surface modem for receiving signals from a telemetry module comprising a controller coupled to an analogue front end comprising a plurality of filter stages, in which the controller is arranged in operation to:

• send a command to the telemetry module to enter autotune mode;
• repeat, for different frequencies across a channel bandwidth range, the steps of:
• receiving a signal of a known frequency;
• and
• processing said signal by determining a magnitude of the received signal at said known frequency;
• until a plurality of signals have been received and processed;
• calculate an optimum set of filter parameters in dependence upon the measured magnitude at each known frequency and a predefined set of filter stage frequency responses;
• and
• set filter parameters of the analogue front end to said set of optimum filter parameters;
• in which and if the magnitude of the received signal at a known frequency is less than a predetermined minimum, the controller is arranged to perform the steps of:
• applying a gain to the received signal;
• and
• reprocessing the signal to determine the magnitude of the signal at said known frequency;
• wherein:
• applying the gain involves adjusting programmable gain amplifier (PGA) gain to increase the signal amplitude;
• and
• the gain to be applied is determined by indexing a preset PGA table.