The equipment connections are as shown in the diagram below. A mixer may be necessary if you want to convert the RF frequencies to desired IF frequencies. In case you do not need a frequency mixer, simply connect the IF OUT cable to the Noise Source, and calibrate.
http://www.tutorialsweb.com/rf-measurements/noise-figure/noise-figure-measurement-techniques.htm
A relatively simple automatic Noise Figure (NF) meter was developed which is using a spectrum analyser as the receiver and logarithmic power detector.
http://gref.cfn.ist.utl.pt/cupido/nfsa.html
http://www.mrs.bt.co.uk/dubus/9004-2.pdf
http://www.wenzel.com/documents/measuringphasenoise.htm
When the 555 ic goes into timing mode (triggered by an output signal from the sound detector amplifier,) the timer output (pin 3) is set into HIGH for a duration set by C2, and R2.
http://www.reconnsworld.com/audio_sounddetectlatch.html