1400 Mhz resonance in lbw jun05 to apr07


Data reduction:
Feb06 with bumps in polA and polB
Apr07 after omt bolts tightened:

 Feb06: Caloff/(calOn-calOff)   show resonances in polA and polB (.ps)  (.pdf):
Feb06: Dynamic spectra lbw of calOff/(calOn-calOff) for 2005(.gif)
Apr07: Caloff/(calOn-caloff) show the polA resonance is gone (.ps) (.pdf):

Introduction (top)

    On 23jun05  a resonance was reported in lbw polA. It appeared after the warmup/cool down cycle of 01jun05. A wider resonance was also seen in polB. In apr07 the lbw reciever was brought down to the lab and the bolts in the the omt were found to be loose. After tightening these bolts, the receiver was reinstalled. Data was taken on 15apr07 and the narrow polA resonance at 1400 Mhz was gone. The wider resonance at 1395 Mhz in polB was still present.

Data reduction:  (top)

 Let Gn be the frequency dependence of a noise source and let Tm be the frequency independent temperature from source m (at least constant over our 100 Mhz band). The the calOn, calOff spectra are : Where  IF is the IF/Lo dependence after the cal injection.
We can remove the major frequency dependence (Gif) using: Over the 100 Mhz band Gcal,Gsky is fairly constant (except for the 1 mhz standing waves) so we get:     So any sharp peaks we get are probably coming from the omt:

Feb06 before omt bolts tightened: (top)

  On 27feb06 calon,off data was taken with lbw covering 1400 Mhz. This data was taken with the hardware 1 second toggle driving the calon for 1 sec then off for 1 second while the interim correlator took 1 second records synchronized with the 1 second tick. This data shows that there is also a resonance in polB of lbw around 1395 Mhz. Looking back at the 23jun05 the polB resonance was also present.

The data:

    The plots of Feb06 Caloff/(calOn-calOff)   show resonances in polA and polB (.ps)  (.pdf):
  1. Top: This is the Caloff/(calon-calOff)*Tcal spectra (scaled to kelvins with the cal value). The black line is pol A while the red line is polB. The dashed blue lines are the 25Mhz band edges (where you expect some dips in the spectra). The polA resonance is at 1399 Mhz with a fwhm of about  2 Mhz. There is a resonance in polB at 1394.5 Mhz with a fwhm of about 5 Mhz. The spectra are from 2400 seconds of data (1200 secs calon, 1200 secs caloff) averaged.
  2. Bottom: This is the same plot with each spectra normalized by its median value. The polA resonance is about 15% of Tsys while the polB resonance is about 9%. The dashed black and red lines show the calvalue versus frequency used when scaling the spectra to kelvins.
    To verify that these resonances were caused by the jun05 dewar warmup/cooldown all of the cal onoffs for lbw during 2005,2006 taken with the interim correlator were looked at.  Those that fell in the 1390-1405 frequency range and had the hybrid out were used to create:
Dynamic spectra lbw of calOff/(calOn-calOff) (.gif):


processing: x101/060227/lbwcalresonance.pro

Apr07 after omt bolts tightened. (top)

    X102 data taken 15apr07 was used to check the receiver. 60 one second dumps followed by 2 second cal on/offs were used. This was repeated twice.
    The plots of  apr07 Tsys/(calOn-caloff) show the polA resonance is gone (.ps) (.pdf):

Apr07 conclusions:

    processing: x101/070415/lbwresonance.pro