Re: Noise Source
There are two major flaws in the circuit in post No 9.
"Resulting in a strong noise source suitable for measurements"
Nope! It should read "Resulting in a noise source far too strong to be suitable for the measurement of normal low-noise equipment and components"
The second flaw lies in the two amplifiers (whose gain will wander with temperature) and also in the imprecise control of diode current. This is not going to be a stable enough source to be worth calibrating to the resolution needed to make noise figure measurements, even if you attenuate the output down to the necessary level.
As you say, the amount of noise from a zener changes very rapidly with voltage. This is the diode telling you that driving it from a voltage source isn't a good idea. Constant current source drive has been mentioned a few times. You've overlooked an important clue.
What frequency range do you want your noise source to work over?
David
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