3 4 5 6 7 io 20 30 40 50 60 FREQUENCY-Mc

Figure 12. Sensitivity vs frequency.

in place of the Unit Null Detector. Here, the generator can be modulated in order to obtain an aural null indication. The sensitivity characteristics shown in Figure 13 apply to this application also with one exception: the 9-//v sensitivity value extends to a lower frequency limit, approximately 1.5 Mc. Therefore, with a broadcast receiver set at 1 Mc, a tunable detector from 0.54 Mc to 60 Mc is obtained (if we include the 0.54 to 1.5 Mc range of the receiver itself). There are, however, several precautions to be taken, such as the elimination of broadcast-station interference. These are described in detail in the mixer instruction book and include shielding of the broadcast receiver and care in selection of the gen-

Figure 13. Block diagram of 1212-P3/1212-A detector system, used as null detector with rf impedance bridge.

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