Looking at the ALFA IF using lband wide..
The ALFA IF was hooked up to the lband wide receiver
on 15may03 and tested. The setup was:
The first set of measurements used a 2 usec time constant and sampled the
system at 1 Mhz. The data was then smoothed to 15 useconds. The plot
shows the 1415 Mhz band when the san Juan radar was pointed at the observatory
(about once every 12 seconds). You can see the downward going spikes when
the radar at 1350 drove the system into saturation. This is probably happening
in the alfa IF or the lbw dewar. The downstairs amplification was after
the 5 Mhz filter that cut out the radar. The radar pulses are 2*5usecs
long. The data has been smoothed to 15 usecs and the compression last for
just 1 sample (15 usecs). The telescope was sitting at az=406.37 and za=7.0544.
This spot gives a strong response to the radar.
lband wide dewar.
1200 to 1500 Mhz filter
ALFA if1 module with 1st lo set to 1675. This places 1415 at 260 Mhz.
The alfa fiber xmter/rcvr using a spare fiber
a splitter with one side terminated (it caused reflections when we tried
to look at both output of the splitter).
6db pad then 5 Mhz filter centered at 260Mhz
260 amplifiers, square law detectors, and then 12 bit a/d converter.
The second set of data was tracking blank sky. A
2 millisecond time constant was sampled at 1 millisecond. The plot
shows the total
power in a 5 Mhz band around 1415 Mhz for 3000 seconds.
Top: 3000 seconds of data has been smoothed to 1 second resolution.
The data has been divided by the median value for the entire span. There
is a jump in the data at second 1920.
Bottom: This is a blowup of the data around the jump. The resolution is
2 milliseconds. The total power jumped by 4%. It jumped back after 60 seconds.