The HP8970B noise figure meter takes the mystery out of noise figure measurements, making them easy, accurate and repeatable. The HP8970B can be used with the 346 or 347 family noise sources. Low instrument uncertainty and automatic second-stage correction make it possible to make accurate noise figure and gain readings, even for low-gain devices. The instrument has special measurement modes for mixer measurement and is capable of controlling external local oscillators and the HP8971B/C noise figure test set. Frequency range: 10 MHz to 1600 MHz (2047 MHz optional). This instrument is the successor to the HP8970A. The major improvement being the storage of four ENR tables. Both “A” and “B” meters can only be calibrated with high ENR noise sources, unless a low noise pre-amplifier is used. Accurate measurement of low noise figures (e.g. less than 10 dB) generally require a low ENR source. So fast switching between ENR tables really facilitates the measurement.

GPIB control: the instrument has two GPIB busses: the System Interface Bus (SIB) and a general purpose bus. The SIB is used to connect a sweep generator, the down converter (e.g. HP8971B/C, aka Noise Figure Test-set) and a plotter, with the 8970 as bus controller. The down converter extends the measurement range to 18 GHz (HP8971B) or 26.5 GHz (HP8971C).

For utmost accuracy it pays off to calibrate the instrument from time to time. Refer to Chapter 5 of the Service Manual, in particular the detector and gain related adjustments. (NB: error on page 5-13: A14TP16 should be TP12).

Noise figure measurements are notoriously difficult to perform well. There is a wealth of literature available, the HP Application Notes 57-1 and 2 are in particular well worth to study. A point of attention often overlooked is the ambient temperature. Make sure the correct temperature is entered in the meter (SF 6.0) and keep the temperature of ambient and sources constant. A difference of about 5 degrees gives 0.1 dB variation in Nf.