Wide band look at AC birdies in 327 rcvr.

 dynamic spectra for the 170 seconds of data (.gif):
 average spectra when the Ac was on and off (.ps)  (.pdf)

    The 2 air conditioners in the dome (18K Btu, 33K Btu) generated a comb with  a 1 Mhz spacing. It was seen in the 327 and 430 Mhz receivers. The comb was coming from the digital portion of the AC unit (used for the thermostat and the hand held communications). A new 33K Btu unit was purchased. It as well as the old 33K Btu unit were fitted with an analog thermostat and the digital control was removed. The smaller 18K Btu unit was not modified.
    On 22feb06 a test was done to see if any 1 Mhz combs remained in the 327 receiver. The test consisted of:

The images show the dynamic spectra for the 170 seconds of data (.gif): The next plots show the average spectra when the Ac was on and off (.ps)  (.pdf):


    The combs from different Ac units had the same comb spacing but there was a frequency offset between combs. There is lots of rfi left in the band when the old Ac was off, but not of it looked like it was part of a 1 Mhz comb.

    Another test would be to try and turn off the new Ac units (if we can find their breakers) and see if and birdies go away...

processing: x101/060222/327ac.pro