Portable test receiver for remote monitoring system

A portable test receiver apparatus for receiving a message signal with bit timing from a remote monitoring system transmitter with alternating current zero crossings having a plurality of transmitting frequencies, wherein said message signal has a plurality of data bit phase flips and corresponding signal nulls providing information about the status of a monitored transformer, said portable test receiver apparatus comprising:

• regeneration means for regenerating the bit timing provided by said remote monitoring system transmitter by utilizing the signal nulls of said message signal that correspond to the alternating current zero crossings in said remote monitoring system transmitter to provide a timing signal corresponding to the data bits of said message signal;
• phase-locked loop means, having a capture range corresponding to the transmitting frequency range of said transmitter, for converting said message signal, via voltage controlled oscillator (VCO) output, to transistor-transistor logic (TTL) levels for digital manipulation;
• frequency detecting means for providing an indication of the frequency of said message signal;
• reference means, driven by a crystal oscillator and connected to said message signal, for providing a constant phase and frequency reference signal for phase flip identification;
• frequency doubling means for doubling the frequency of the VCO output of said phase-locked loop means to eliminate 180.degree. phase flips between bits of said message signal;
• phase comparison means for identifying phase flips by comparing the VCO output signal from said phase-locked loop means to the reference signal provided by said reference means;
• microprocessor means, connected to said regeneration means and said reference means, and said phase comparison means, for demodulating said message signal using the bit timing from said regeneration means and the output of said comparison means to a data bit signal corresponding to said message signal.