where P is the probability that a datum will be a contaminant. No general form for the polynomial has yet been found.

5

p2(2.5 – 1.875 P + 0.375 p2) = (2)2 (10 - 7.5 p + 1.5 p2)

(믈)

where P is the probability that a datum will be a contaminant.

small data groups, however, it is easy to select the medians rapidly, greatly reducing the data to be processed further. For these reasons, the efficiency of the data group median method in terms of relative speed of processed data production may be much better than the ratio of medians to total data (1/n).

The CRF calculations are also applicable to the improvement of system reliability by the use of active circuit redundancy. The outputs of several identical circuits (whose inputs are tied together) can be ranked electronically and only the median output used. If P is the failure rate for one of the circuits, then the overall failure rate would be reduced to CRF times P if the failure rate of the median selection circuit was negligible by comparison.

References:

C1. Natrella, M. G., Experimental Statistics, NBS Handbook 91, Washington: GPO, 1963, Chapter 17.

C2. Ku, H. H., (ed.), Precision Measurement and Calibration, NBS Special Publication 400, Washington: GPO, 1969, pp. 346-354.

APPENDIX D

DEFINITIONS OF MIXER TERMS

Conditions, standard mixer measurement: specified values for system variables outside the mixer (or diode) of which the measured values are functions. When the measurement conditions are standard, the measured values may be attributed to the mixer (or diode). When one or more conditions are not standard during the measurement, a correction may be made for the difference or the resulting change in the measured value covered by an additional uncertainty allowance. The measurement conditions to be specified include some or all of the following: Local-oscillator and intermediate frequencies; terminating immittances at the local-oscillator frequency and at all input frequencies for which there is a significant output response (e.g., nonreflective at all frequencies); localoscillator power available to the mixer; intermediate-frequency and d-c loads and external bias, if any; physical temperature of diode or holder; and, for diode characterization, the physical construction of the diode holder and, if tunable, the tuning procedure to be followed. Signal levels are to be sufficiently small that the measured parameters are independent of signal strength. Other conditions to be standardized are noted under individual parameter definitions.

Conductance, intermediate-frequency output, G: the real part of the mixer intermediate-frequency output admittance. Standard mixer measurement conditions apply. Intermediate-frequency output conductance is commonly expressed in units of ohms (of its reciprocal). The traditional but erroneous use of the term "intermediate-frequency impedance" for this quantity is deprecated.

Conversion Loss, L: the ratio of available r-f power at a single designated signal frequency to that part of the available (or delivered) intermediate-frequency power which is a function of the r-f power (excluding that part which is independent of input). Standard mixer measurement conditions apply. When delivered intermediate-frequency power (to a specified load) is used, the loss is referred to as "conversion insertion loss."

Noise figure (noise factor), average, F: for a multiport with specified terminating immittances, the ratio of (1) the total noise power available from its designated output port (or delivered to a specified load) within a designated output frequency band, when the noise temperature of all terminations is a standard reference temperature, to (2) that portion of (1) which is a function of the noise temperature of the designated signal input termination within a designated signal input frequency band. age noise figure is a dimensionless power ratio, commonly expressed in decibels. In measuring mixers and mixer diodes, there are two average noise figures of common interest: (1) intermediate-frequency average noise figure, and (2) overall average noise figure:

Aver

Intermediate-frequency average noise figure, Fi: the average

noise figure of an intermediate-frequency amplifier. Its general dependency upon intermediate-frequency output conductance is to be particularly noted.

Overall average noise figure, Fo: the average noise figure of the cascaded combination of a mixer and high gain intermediate-frequency amplifier.

When used to characterize a mixer, standard mixer measurement conditions apply, with the following additional qualifications: The intermediatefrequency average noise figure is standard (usually ≥1.5 dB), and the passband of the intermediate-frequency amplifier is sufficiently narrower than that of the mixer so that the mixer conversion loss and output noise temperature are constant over the intermediate-frequency passband. When these conditions are met, the prefix "standard" may be used to distinguish both the intermediate-frequency and overall average noise figures, and the subscript "s" added to the symbols, i.e.,

When the overall average noise figure is measured with a nonstandard (but known) intermediate-frequency average noise figure, the standard overall noise figure may be calculated from:

When the intermediate-frequency average noise figure is not known, but has a known lower bound, Fib, the following inequalities may be useful for qualification testing: