Tsys forMathew's 430Mhz test feed
A cal diode was installed on the 430 dipole of
mathew's on the ch. Calixto reported that the cal at 430Mhz was 42.1 K.
The system temperature was measured using the cal. The setup was:
The plots show the
cal deflection and the system temperature (.ps) (.pdf):
The telescope was parked at az=275(dome side) ch=8.8 degrees (this is an
lst around 13 Hr).
The cal was toggled on 1 sec, off 1 sec. This continued for 960 seconds.
1 Mhz around 430 was detected with at 2 millisecond time constant and sampled
at 1 khz.
The median value for each 1 second was then used for the cal on, off
Tsys for the receiver is 152 K (if the cal is 42.1 K).
There is an oscillation in the cal of about 220 seconds. The cal is currently
configured to use a constant voltage source. It needs to be switched to
a constant current source.
Fig 1 top: Total power vs time for the cal on. These are the 1 second medians.
The units are linear in power (A/D counts). The spikes are caused by lightning.
Fig 1 middle: Total power vs time for the cal off.
Fig 1 bottom: (CalOn-calOff)/(median(calOn-calOff). This shows the fractional
change in the ratio vs time. Looking at the individual calOn, calOffs
you see that the variation is not present when the cal is off. The ripple
is coming from the cal.
Fig 2 Top: Tsys vs time using 42.1 for the cal Temperature. The avgerage
value is 151.8 K.
Fig 2 bottom: A sine wave was fit to Tsys vs time. The Amplitude is 3.3K
and the period is 219.7 seconds. The amplitude does not match with the
fraction of cal from page 1. 3% of 42.1K=1.2K not 3.3 K. So maybe
some of the oscillation is in the cal off too??