1400 Mhz resonance in lbw jun05 to apr07
Feb06 with bumps in polA and polB
Apr07 after omt bolts tightened:
show resonances in polA and polB (.ps) (.pdf):
spectra lbw of calOff/(calOn-calOff) for 2005(.gif)
Caloff/(calOn-caloff) show the polA resonance is gone (.ps) (.pdf):
On 23jun05 a resonance
was reported in lbw polA. It appeared after the warmup/cool down
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
Let Gn be the frequency dependence of a noise source
and let Tm be the frequency independent temperature from source m (at
constant over our 100 Mhz band). The the calOn, calOff spectra are :
Where IF is the IF/Lo dependence after
- Scalon =(Tsky*Gsky +Tomt*Gomt +Tcal*Gcal)*Gif
We can remove the major frequency dependence (Gif) using:
Over the 100 Mhz band Gcal,Gsky is fairly constant (except for the 1
standing waves) so we get:
So any sharp peaks we get are probably coming from
omt bolts tightened:
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
there is also a resonance in polB of lbw around 1395 Mhz. Looking back
at the 23jun05 the polB resonance was also present.
The plots of
Feb06 Caloff/(calOn-calOff) show resonances in polA and
To verify that these resonances were caused by the
dewar warmup/cooldown all of the cal onoffs for lbw during 2005,2006
with the interim correlator were looked at. Those that fell in
1390-1405 frequency range and had the hybrid out were used to create:
- Top: This is the Caloff/(calon-calOff)*Tcal spectra
with the cal value). The black line is pol A while the red line is
The dashed blue lines are the 25Mhz band edges (where you expect some
in the spectra). The polA resonance is at 1399 Mhz with a fwhm of
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.
- Bottom: This is the same plot with each spectra
median value. The polA resonance is about 15% of Tsys while the polB
is about 9%. The dashed black and red lines show the calvalue versus
used when scaling the spectra to kelvins.
spectra lbw of calOff/(calOn-calOff) (.gif):
- The top is polA, the bottom is polB. The vertical axes counts the
The first 63 spectra were only 3 Mhz wide. Around 63 the bandwidth
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.
- The 01jun05 warmup,cooldown caused resonances to appear in both
polB of lbw.
- The polA resonance is at 1399 Mhz, .15 of Tsys, and fwhm
- 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
us something about how they are being created.
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):
- 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.
- 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.