and are well known to those of skill in the art and as such will not be described herein the general operation of the circuitry on the probe board 14 is as follows the waveform synthesizer 44 of the dsp 30 is directed by software program instructions provided to the dsp by the system processor in response to operator instructions to define the waveform pulse sine complex sinusoidal saw triangle desired to perform a test the frequency synthesizer 45 of the probe processor 20 is then directed by software program instructions in the dsp to cause the waveforms that are programmed and generated by the waveform synthesizer 44 to be transmitted at the specified frequency the output waveform from the waveform synthesizer 44 is sent into the transmit amplifier 43 the transmit gain controlled by the transmit gain control 42 is fixed for the duration of a run the transmit amplifier 43 is a high precision push pull style amplifier that will inject the waveform directly into the circuit under test the primary receive source select switch 49 is instructed to tie the receive amplifier 40 in parallel with the transmit amplifier 43 the receive amplifier is a high precision 3 stage op amp amplifier meaning that the amplifier will provide a precise fixed gain to the combined stimulus reflection signals prior to being injected into a circuit to be tested the signal is passed through a delay loop introducing a time delay.