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Figure 10. Schematic of the Type 1212-P3 RF Mixer.

Figure 11. Sensitivity (open-circuit voltage from 50-ohm source, for 1% meter deflection) vs local-oscillator drive for the 1212-P3/1212-A detector system.

CRYSTAL CURRENT-^ia again limited by local-oscillator tuning resolution, tuning difficulty, etc., is GO Mc. Aside from these considerations, the mixer performs perfectly well up to at least 150 Mc. Null Detector

The response of the Unit Null Detector is approximately logarithmic, rather than linear. For this reason, it does not have a gain control. The system, is, therefore, usable only as a null detector, and, in this application, it is a sensitive, easy-to-use instrument. The principal characteristics of interest are the variation of sensitivity with diode current (Figure 11) and sensitivity over the frequency range (Figure 12).

Figure 13 is a block diagram of the detector shown as part of a complete rf bridge system. The local oscillator is alwrays set higher than the generator frequency when the operating frequency is below 10 Mc, in order to minimize the local-oscillator voltage that gets through to the mixer output.. Use with a Broadcast Receiver

The Type 1212-P3 Mixer can also be used with a standard broadcast receiver

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