which is then corrected to by combining it with [] and []. The "times R" module in Figure 7b can be the PCC of Figure 6 with fy?. at both inputs. Before we can go on to the third example of an exact PCC and its associated PRR, we must discuss the problem of receiving the pilot signal. PCC’s and PRR’s are usually IF circuits, while the pilot is a microwave signal. We must accurately transfer the phase information in the pilot signal to the IF input signal to the PCC. A receiver which does this is called a coherent receiver. The best known coherent receiver is the phase-locked receiver shown in Figure 8a. The average, or slowly varying, part of the pilot signal phase is divided by n + 1, the ratio of the microwave to IF frequency. Another kind of coherent receiver is shown in Figure 8b. The pilot signal for this receiver must consist of two carrier signals or "tones" transmitted from the same pilot antenna. These tones can be the upper and lower sidebands produced by balanced modulation. The IF output of the "two-tone receiver" in Figure 8b is simply a doubled version of the modulation, which contains the phase information in each of the pilot tones divided, again, by the pilot/IF frequency ratio. In Figure 8b, we assume that the LO frequency, [] lies between those of the two pilot tones, f and f , so that mixer 1 Z Ml produces the two lower sidebands [] . These are separated by band pass filters, and one of them is amplified to a level sufficient to serve as the LO for M2. M2 is an upconverter. Hence, its output phase is
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