A relatively simple automatic Noise Figure (NF) meter was developed which is using a spectrum analyser as the receiver and logarithmic power detector. The circuit makes use of the X and Y output signals available on most spectrum analysers. It processes these signals to control a noise head and obtain Y, Gain and NF values that are displayed on digital or analogue meters.
This simple instrument will enable easy real time alignment and optimization of preamplifiers and converters for best performance, on the full range of the noise head and spectrum analyser.

The article was presented in UKW-Berichte 2/98 and here it is an english version, you can download "Automatic Noise Figure and Gain Measurements With a Spectrum Analyser" (171K)
The diagram in a gif file "Schematic diagram"(99K)

The PCB ready to print in Postscript, PDF and PCL5 (direct to LASER printers at 1:1 and 2:1), at "PCB prints" (219K)

My prototype:

Front panel view.

On the photo, the main circuit is the bigger board.
The left board is the power supply, while the bottom board is just an electronic switch to select the display functions (this switch replaces two mechanical switches, and is not described in the article).
Also attached to the main board is a set of adjusts to null the offsets of the opamps, This is needed if lower quality IC's are used, or if ultimate performance is desired.

Results obtained so far are in good acoordance with the values obtained on modern commercial test equipment.

Any comments: Luis Cupido