1 Mhz comb in 327 receiver (coming from AC units in dome).

Links to plots:
the single birdie characteristics (.ps) (.pdf):
Dynamic spectra shows the birdie drift rate (.gif):
Looking at all of the 1 Mhz comb birdies in 310-340 Mhz (.ps) (.pdf)
Birdie changes when we turn off the Old AC (.gif):
Birdie changes when we turn off the New AC (.gif):

Initial problem

    The experiment a2057 was doing long integrations at 327.38 and 310.4 Mhz. After getting rid of the 16Khz comb (from the alfa motor controller) a large narrow birdie showed about in both of these bands. It wandered by many KHz.

Characterizing the birdies: (top)

Summary of the birdie characteristics: (top)

The birdies are coming from  the  air conditioning unit. (top)

    On 12oct05 we looked in the turret room for the birdie. The setup was:     We used the birdie frequency from the 327 receiver to track the birdie in the tektronix spectrum analyzer. The first pass through the room showed nothing. When the probe (which is not very sensitive) was raised up in the air close to the ac unit above the focal point (the old Ac unit) the birdie appeared.  The plots show the birdie changes when we stopped the AC  unit:     Shutting off the Ac unit caused the birdie to change drift directions but it did not go away. When the ac unit is turned off with the portable control, the compressor is shut off but the  digital control board in the AC unit remains on (so that it can tell when you want to turn it back on). When we shut off the breaker to the Old AC unit, the AC digital control unit is shut off. This caused the birdies to go away. So the birdies are coming from the digital control portion of the AC.

    We need to change the AC unit from a digital control to an analog version (like we did in the vertex shelter). This should get rid of the birdies.

processing:  x101/051012/accomb/327acall.pro, 327acimages.pro, 327step.pro