Timing setup

    The test box applies 0V to U3 pin3 via TP9. This causes the
    micro to generate a self calibrating test pulse on TP10.
    
    The ANT Unit provides two bursts at frequency F1. The first
    sets the timimg in motion. The second gives a pulse out of
    the comparator the start of which must be aligned with the
    end of the test pulse.

    First align it looking at the pulses then put the scope on to
    "ADD" which gives a narrow difference pulse (positive or negative).
    Setting involves reducing this to zero. This is not possible
    due to timing jitter. The ideal is where there is a mixture of
    positive and negative spikes.

