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

Plots:
 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)

• Tsys*Gtot=Scaloff=(Tsky*Gsky+Tomt*Gomt)*Gif
• Scalon =(Tsky*Gsky +Tomt*Gomt +Tcal*Gcal)*Gif

• Tsys=Scaloff/(Scalon-Scaloff)= (Tsky*Gsky+Tomt*Gomt)/(Tcal*Gcal)

• Tsys=(Tsky+Tomt*Gomt)/Tcal

Feb06 before omt bolts tightened: (top)

The data:

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.

• The top is polA, the bottom is polB. The vertical axes counts the calon,offs. The first 63 spectra were only 3 Mhz wide. Around 63 the bandwidth widens with no extra power at 1400 or 1395. Around 66 the extra power shows up in polA and polB around 1400 and 1395. The  increase started after 01jun05 so the resonance were a result of the warmup,cooldown.

Conclusions:

• The 01jun05 warmup,cooldown caused resonances to appear in both polA and polB of lbw.
• The polA resonance is at 1399 Mhz, .15 of Tsys, and  fwhm of  2 Mhz.
• The polB resonance is at 1394.5, .09 of Tsys, and 5 Mhz fwhm.
• The frequency shift and bw difference of the two resonance should tell us something about how they are being created.

Apr07 after omt bolts tightened. (top)

• The top plot shows the 60 second average bandpasses. Black is polA and red is polB. The lower frequency polB spectra differ because the correlator attenuators changed by 1db. The dashed green/blue lines show the bandpass edges and overlap.
• The center plot shows calon-caloff  for the two measurements.
• The bottom plots shows AvgSpc/(calOn-caloff). The two measurements have been averaged. The vertical scale is in units of Tsys. The slope in the spectra is because we have not multiplied by the changing cal value across the 100 Mhz. This division should cancel any frequency dependence downstream of the cal injection. At the bottom left the old spectrum is plotted (with an offset). You can see that the polA resonance at 1400 Mhz is now gone. The polB resonance is still present but has moved a few Mhz down in frequency.
  

Apr07 conclusions:

• The narrow polA resonance that first appeared in the jun05 lbw warmup is gone. Tightening the bolts in the omt made the difference.
• The wider polB bump is still present and has moved down a few Mhz.

 home_~phil