Can I measure noise figure with a spectrum analyzer, a preamp and a signal generator?

You can make approximate measurement of noise figure with just a spectrum analyzer and a preamp. Using just a spectrum analyzer, a preamp and a signal generator that cover the frequency(-ies) of the device being tested. The accuracy of this technique, while not as good as the Y factor technique calling for a calibrated noise source, is about as good as the analyzer's amplitude accuracy at the frequency(-ies) of interest. Here are the steps:1. Use the signal generator and spectrum analyzer set to the frequency you wish to measure noise figure to measure the gain of the device. Call this value Gain(D).2. Similarly, measure the gain of the preamp. Call this value Gain(P).3. Disconnect any input from the spectrum analyzer and set its input attenuation to 0 dB. With no connection to the preamp's input, connect its output to the spectrum analyzer's input. You should see the displayed average noise level of the analyzer increase when you make this connection.4. Terminate the input of the device to be tested with its characteristic impedance and connect its output to the preamp's input. When you do this, the noise level displayed on the spectrum analyzer should increase.5. Set the spectrum analyzer's video bandwidth (VBW) to be 1% or less the value for the resolution bandwidth. Press the Marker Function (MKR FCTN) key, then the Noise Marker On soft key. Position the marker to the frequency where you wish to measure noise figure. Read the marker noise power density reading in dBm/Hz and call it Noise(O).6. The noise figure, NFig of the device under test can then be computed as: NFig = Noise(O) - Gain(D) - Gain(P) + 174 dBm/HzFor more information on this topic, see literature number 5952-8255, Noise figure Measurement and 5966-4008E Noise Measurement with Spectrum Analyzers.