This document describes the receiver controls. All receiver controls are electronic (as opposed to manual) and under the direct control of the pulse programmer (PP).
The receiver controls gain by switching various stages in or out of the signal path. The stages are arranged so that gain changes always occur in approximately 6 dB increments. The total control range is 90 dB.
Receiver gain is set by incorporating the Rec_gain() primitive in a state. This primitive accepts a single argument which specifies gain in dB in the range of 0 to 90. Values are always rounded to the nearest multiple of 6 dB. The primitive is commonly included in the default state declaration so that the gain will be the same in all states of the program. Since the gain stages are controlled be relays, response is not instantaneous; approximately 1 mS should be allowed for a change in gain to occur.
At a gain setting of 0, the receiver input sensitivity is approximately +4.0 dBm (1.0 VPP) for full scale digitizer output. At a gain setting of 90 dB, the receiver input sensitivity is approximately -86.0 dBm (31.0 uVPP) for full scale digitizer output.
The receiver includes anti-aliasing filters which filter the detector output before it is applied to the A-D converters. The low-pass cutoff frequency of these filters is under the direct control of the PP.
The frequency range from 400 Hz to 102.4 KHz is handled by digitally tunable active filters that have a tuning resolution of 400 Hz. These are eight pole Bessel filters.
The frequency range above 102.4 KHz is covered by four fixed frequency filters. These are four pole Butterworth filters with cutoff frequencies of 250 KHz, 500 KHz, 750 KHz and 1.0 MHz. Additionally, the receiver can be instructed to bypass the filters all together.
Receiver gain is set by incorporating the Rec_filter() primitive in a state. This primitive accepts a single argument which specifies gain in Hertz in the range of 400 to 1.5e6. Values are always rounded to the nearest available filter frequency. Values greater that 1.0e6 result in the filters being bypassed. The primitive is commonly included in the default state declaration so that the filter frequency will be the same in all states of the program.
The receiver blanking switch is under the direct control of the PP. The receiver gate is controlled by incorporating the Rec_gate() primitive in a state. This primitive accepts a single argument with a value of either 0 or 1. A value of 0 opens the gate switch (blocks the signal), a value of 1 closes it (allows the signal to pass).
If the Rec_gate() primitive is not included in the default state, then the value will default to 0 (open, blocking the signal) for all states. Thus it is usually only necessary to include the primitive in states where the the gate must be closed (signal allowed to pass).