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The forward direction. 0002 in. E – 1), (1) where i is the direct current, A and a are constants, and E is the voltage across the barrier. Thevoltage Eis given by E= E’–ir, (2) where E’ is the voltage applied to the rectifier and r is the spreading resistance in the semiconductor at the contact point. 7 shows the logarithmic characteristic of a typical unit, as observed by Torrey. semilogarithmic; hence a plot 1H. Q. North, Fiual Report, “VJelded GermaniumCrystals,” Contract OEMsr262, Order No.

5 db (or about 9 times). [The values substituted in Eq. ] In using Eq. (28) for calculating the receiver noise figure we must remember that the results are accurate only in so far as the r-f and i-f impedances are maintained the same in the combination of mixer and i-f amplifier as they were in the equipment in which the separate quantities were measured. Another quantity useful in crystal-noise measurements and analysis is the Y-factor. It is defined as the ratio of available output noise power NOof an amplifier whose input terminals are loaded by a crystal mixer to the same quantity NO.

The effect of local-oscillator power level on receiver noise figure can be calculated from the data of Fig. 17 by means of Eq. (28). The calculated curves for three values of i-f amplifier noise figure are shown in Fig. 18. 8 ma and it is in this range that crystal mixers are ordinarily operated. Since the minimum is broad, the choice of operating level is not critical. It is obvious from the curves that the rni~mum ii 34 PROPERTIES OF THE CRYSTAL lWCTIFIERA [SEC. 26 broader for “ quiet” crystals and would in fact disappear for a crystal having a noise temperature of unity for all values of rectified current.