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automatic control of input attenuator.
In the user interface there is a red 'ov' indicator that goes on when the antenna voltage is too high.
Is it possible to sample that 'flag' and use it to controle an attenuator via a IO-pin on the BB? Ok, there have to be som feed-back to the spectrum display and waterfall to sho the correct level - ok it will be with lower S/N ratio but without overload and mystic sporius signals.
Any comments :-)
Is it possible to sample that 'flag' and use it to controle an attenuator via a IO-pin on the BB? Ok, there have to be som feed-back to the spectrum display and waterfall to sho the correct level - ok it will be with lower S/N ratio but without overload and mystic sporius signals.
Any comments :-)
Comments
The current FPGA logic behind the OV indicator is as pessimistic as it could be and almost certainly wrong. Right now if one single sample overflows the ADC the OV indicator will get lit and persist long enough to be seen. That doesn't really indicate a substantial overload condition that will lead to increased IMD products seen in the waterfall etc. The logic really needs to be a threshold/averaging function of some sort.
The +20 dB amplifier / matching buffer ahead of the ADC is a fixed gain block. So yes, you'd have to have new OV logic trigger a GPIO pin and control an external attenuator (with appropriate hysteresis so it isn't pumping on and off all the time).