RA3WDK `s Homepage

RF & Nf Measurement

 

 

    Noise figure is a one of main performance parameter for HAM VHF/UHF/SHF systems. A low noise figure provides improved signal/noise ratio (SNR) for our EME/MS setup. If you want to try make good low-noise amplifier (LNA) - you must improve noise figure measurement accuracy. Is this easy work ? But we can do it !

    I use the Y-factor method with different noise source : Home made source (p-n channel or diode), industrial noise source, "cold" horn.

Fundamentals TRX system = THOT(1/(Y-1)) - TCOLD(Y/(Y-1))

Fixing Measurement Errors

1. Use big difference between THOT and TCOLD . ENR must be more than 10-15 db

2. Use attenuator 10-20 db between source and LNA, because that S11 of source or LNA not optimal (SWR=1)

3. Use broadband IF section before the detector, but use IF section with Quality Band Pass Filter (BPF).

4. IF section must have good perfomance IP1 , IP3

5. Detector must have stability and accuracy more than 0,05-0,1 db in band 20-25 db

 

You can download NF calculator - NoiseFigure_v4.xls

Meter for measurment Noise of Moon and Sun

Digital Noise Meter

Noise Meter uses Log.Detector AD8307 , ADC by MCU ATmega16, Precision voltage regulator LM4040A, thermometer DS18D20 in noise source

IF section 28 MHz

 

"Cold" horn for measurement Noise factor of LNA on 5,7 Ghz and 10 Ghz

 

 

Measure NF my 1296 MHz system