Simple Precision Automatic Noise Figure Indicator

by OK1DFC 2007 and 2020


After 13 years, I went back to the original version of SPANFI and modified it a little for today use. Having started a lot of work in microwave bands in recent years, it proved necessary to equip my station with a new generation noise meter. While operating on the MW, you need to keep a constant eye on the moon noise, so I decided to build a new SPANFI. Several images and schematics as I modified the device in the following sequel. September 2020. First step was 56dB amplifier. The detector design is original and the base is catalogue sheet AD8307, I just modified the PCBs. The output circuit board "control board" is based on the Michael DB6NT device. I found a very useful assistant in this facility for EME microwave use.

Version and upgrade of 2020 year




Figure of the bottom and top sides of PCB with 3xERA3 MMIC amplifier.




Detector Area PCB Images with AD8307




Assembled unit



A view of the front and back panels of the new SPANFI.



A view of the internal layout of the device. AC/DC power supply, 3 boards of unit, SMA relay which is during TXing period switching input to 50ohm load.

The first test of measurement after calibration was the noise of the sun in the 24 GHz band. Unit showing 12,2dB Sun noise, same value as measured on SpectraVue SW program on SDR..

Version of 2007 year

Real first stage of SPANFI amplifier - 10/04/2007

New design with two band-pass filters, 144 and 432 MHz switched by OMRON signal relay.

Block diagram and schematic


Data sheet of AD8307

PCB board with amplifier and band pass filters
Amplifier, detector and programmable attenuator for 10 - 20 - 30 - 60 dB

AD 8307 detector

SPANFI including two ATT, one of them describe above, second one is for fine attenuation set up 1 - 2 - 4 - 8 - 16 - 32 - 64 dB

View to front panel.

View to rear panel.

Whole unit above 20/08/2007

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