Checking JFET Noise

JFET noise is seen when the detectors are at 4 K. In this case the detectors act like a short so you will see only the hash-like white noise caused by the first stage of amplification: the cold JFETs in the dewar. This is a nice test of the preamps and the data system that you can do before cycling the dewar.

In detail: If you attach the preamps to SPARO and connect these with the data system, some "hash" due to JFET noise will appear on the strip charts. This noise is had the following amplitude in the Austral summer 1999-2000:
Settings:

preamp gain = 10,000,
global attenuation of the data program = 1000
strip chart attenuation = 4
chops/frame = 2

With these settings you should see:

R-array: 1/16 - 1/8 inch amplitude noise (except for R5 and R6 that have about 3/16 inch)

T-array: 1/8 inch amplitude noise (except for T7 and T9 that have about 3/16 - 1/4 inch)

It doesn't matter whether the bolometer bias switches are on or off for these measurements. (The bolometer bias switches are located on the preamps.)

Contact g-novak@nwu.edu. Last updated Feb 9, 2000.