path length compensation. The method has similarities to the aforementioned retro-directive approach with the transmission medium being the coaxial cable. Phase errors were held to within 1° rms over a 600 meter baseline by this method. Similar methods have been proposed for reference distribution in the Cyclops concept (reference 14). One such method (reference 14) is illustrated in Figure 4. On the right side of the figure is shown a voltage controlled oscillator which. without control, would operate at a frequency and have a phase offset The output of this oscillator is transmitted via coaxial cable to a reference module which provides the reference frequency, Wo. Propagating along the line the VCO signal acquires a phase displacement according to the length of the line, The phase displaced VCO signal is then heterodyned with the reference frequency, Wo, at the reference module. The resulting lower sidetone has the same frequency as the VCO signal but has the opposite phase displacement. This lower sidetone is then sent back along the same coax to the originating module. This return signal will experience an almost identical phase displacement on the return path so that when received it has only the phase residuals An additional heterodyning results in an upper sidetone with a frequency identical to the reference, Wo, but having a phase residual due to the VCO frequency offset Using identically zero when the loop locks. Thereafter, the regenerated the lower sidetone produced in the same operation to control the VCO, a phase locking operation is initiated so that the offset, , is
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