Birdie pixel 0b of alfa receiver

resolved 08sep04 (see below).

    A birdie has been seen in Pixel 0b of the alfa receiver  near 1380.7 Mhz. It is  .5*tsys in amplitude and has a fwhm of .7 Mhz (900 second average). Over a 15 minute integration it can wander up to a few Mhz. The problem has been there since at least 21aug04 (the earliest data set i looked at). On 7sep04 the first LO (high side) was moved up by 1 Mhz and the position of the birdie moved down by 9 Mhz. The LO was moved down 2 Mhz and the birdie in the rf band moved down by 18 Mhz.  If this is an intermod, then it is the 9th harmonic of the 1st LO beating with a hiFreq birdie in the system.  The hiFreq birdie would be at:

birdieInRf= 1380.70
HiFreqBirdie= (lo1*9) + (if1 - (rfCfr-birdieInRf))= 14960.7 Mhz
    On 03sep04 a 15 minute drift scan using  100 MHz centered at 1385 Mhz was taken.  The 900 records were averaged together. The plots show the birdie in pixel 0B.  The red linear are polA and the green lines are polB. The plots are labeled B1(pix0) thru B7(pix6).

Resolution of the problem.

    On 08sep04 the module that converts from RF to IF and then to fiber was replaced for  pixel 0 of alfa. After doing this, the birdie went away. When this same module was probed in the lab, the birdie was present.
processing: x101/040903/oscpix0b/