1400 Mhz resonance in lbw pola
The lband wide dewar warmed up and worked on 01jun05.
A broken cal cable for polB was replaced. After the receiver was cooled
down again a bump appeared at 1400 Mhz in polA. Lbw
spectra at 1400 Mhz (.ps) (.pdf)
show the bump in polA.
This problem did not exist before the dewar warmup and
cool down on 01jun05. It is probably coming before the cal injection. Most
resonances in the omt occur in both pols (more
info) so it is a bit strange that we only see it in one polarization.
Top plot. 25 Mhz spectra centered at 1400Mhz. The same spectra was taken
with 4 different paths through the downstairs iflo (4 sbc). This shows
that the bump must be before the 2nd mixer downstairs. Black is polA and
red is polB. The cal Deflection (calOn-calOff) is also plotted: green polA
and blue polB. You do not see the bump in the cal deflection. So the problem
is either not multiplicative, or it is before the cal injection (or both).
Bottom plot: The spectra in kelvins
Notes: These spectra were taken at noon so they look a little ratty
do to the scintillation.
Note 07mar06: Resonances were created
in polA and polB: