IF2 Programmable Gain linearity

27dec06

The downstairs if2 has an 11 db step attenuator (1db steps) followed by 3 10 db amplifiers. These amplifiers can be switched in/out under computer control.
On 27nov06 the linearity of the programmable gain was tested using the 327 receiver looking at the sky. The programmable gain was stepped from -11 db (atten all the way in) to +30db (the 3 amps switched in). At each 1 db step the power in polA and polB was measured using the power meter and recorded.
The plots show the power in the IF2 while the gain was stepped (.ps) (.pdf):

The top plot shows the power while the gain was changed. The black line is polA and the red line is polB. The dashed vertical green lines are where each 10db amp was switched in (at 1db the first 10db amp is switched in and then 9db of attenuation is added).
The second plot shows the difference in powers PolA-PolB. The difference at low gain is caused by the low power level going into the power meter. The 4.5 db jump at 21 db is caused when the 3 amplifier is switched in. It must have a gain of 14.5 db rather than 10 db

We should fix the 3rd amp to be closer to 10db. The datataking tries to adjust the power levels using the current settings and the measured values. A discontinuity of 4.5 db will mess up this algorithm.

Processing: x101/061127/rdpwrif2.pro
page up
home ~phil