Birdie pixel 0b of alfa receiver

23mar05

A birdie has been seen in Pixel 0b of the alfa receiver near 1430 Mhz during experiment a2010. It was not in any other beam or polarization. The band in use was 1335 to 1435. The birdie appeared on 21mar05 and remained for the next few days. It would wander between 1429 to 1435 over a few hour run. This biridie looks similar to the birdie that was found in alfa pixel 0b back in sept04. The observing runs for a2010 started around midnight and ran for about 5 hours. The birdie was seen on:

21mar05. A2010 sees the birdie.
22mar05.

A2010 sees the birdie
Right after a2010, x111 rfi monitoring was run. The lbw receiver did not see any birdie around 1430 MHz in either polarization.
Data was taken with alfa at 12 noon centering at 1385 and at 1430 Mhz. The birdie was not seen.
Pulsar search data taken around 19:00 hours did not show the birdie. It was sampled at 64 Usecs.

23mar05: A2010 sees the birdie.

The plots compare the birdie from sep04 and mar05:

Birdie shape sep04, mar05 (.ps) (.pdf) : This shows a 1 second integration taken 03sep04 (top) and 22mar05 bottom. The frequencies are different but the shape is similar
Dynamic spectra sep04, mar05 (.gif): This show 600 seconds of data for 3sep04 (top) and 22mar05 (bottom). The birdies drift slowly in time.
Temperature dependence of the birdie (.ps) (.pdf): This plot shows the temperature dependence of the wandering birdie. The different colors mark different days.

Top plot: birdie frequency vs date
Middle plot: gregorian room temperature for the birdie times.
Bottom plot: The gregorian room temperature versus the birdie frequency.

The sep04 problem was traced to the module that converts from rf to if and then to the fiber. It was replaced and the birdie went away. An oscillation was later seen in the lab with the module that was causing the birdie.
It is most likely that this is a recurrence of the same problem.
The frequency dependence of the birdie with the temperature in the gregorian dome shows that the problem is inside the dome. The measurements later in the day when the birdie was not seen may be related to the warmer room temperatures during the day..(see the turret room temps for the daily temperatures).
On 24mar05 at 15:00 ganesh replaced this module with the spare module. We'll have to see if the birdie goes away.

processing: usr/a2010/mar05osc/doosc.pro, doosc_freq.pro

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