6334 Transmission Check
- Agreement between expected signal and measured signal is good, indicating
no major unexplained loss of signal:
- Expected signal is 593 integ-units/Jy, and measured signal is 525 integ-units/Jy.
-
Numerous approximations are involved, and total uncertainty in expected
signal is at least 30%, perhaps more.
-
Measured signal comes from Sharon Loverde's memo: 525 integ units per Jy
- This assumes a four arcminute beam
and is extrapolated to no atmospheric absorption.
- It is based on NGC 6334 data as a function of tau, from
Austral Winter 2000.
-
Expected signal comes from the following calculation:
-
1 Jy into SPARO is (10-26 Watts m-2 Hz-1) (Atel) (Delta-nu) = 2.57 x 10-16 W
-
Atel = Area of telescope = [(pi/4)(0.7)2 m2]
-
Delta-nu = [6.7 x 1011 Hz] [0.1]
-
reduce by (tt)(etach)(etaAC)(twd)(tc) to get 1.76 x 10-18 Watts
-
Values assumed: (tt)(etach)(etaAC)(twd)(tc) = (.8)(.85)(.9)(.6)(.0187)
-
(.8)(.85)(.9)(.6)(.0187) = 6.87 x 10-3
-
Definitions and values are explained in
Tom's Table of SPARO characteristics
-
Multiply by average responsivity of 4.1 x 108 V/W to get 7.2 x 10-10 V
- Responsivity is averaged across all channels (R and T) using data on web.
- Responsivity is estimated as (1/3)(S-closed) + (2/3)(S-open) [as is appropriate for 200 K].
- A more careful analysis of pre-upgrade and post-upgrade load curves
(see
Tom's Table of SPARO characteristics) yields essentially the
same result as this simple interpolation.
-
Multiply by preamp gain of 10,000 to get 7.2 x 10-6 Volts into data system
- Multiply by (8,200,000 mac-units per 400 mv)(4 integ-units/mac-unit) to
get 593 integ-units per Jy.
-
The units are discussed in the data analysis units document
-
The above conversion from peak-to-peak amplitude of AC signal
input into data system
to demodulated signal stored/displayed by Mac is given in logbook 5
page 73, and was also checked by Dave Chuss in Austral Summer 2000-2001
and recorded
in logbook 6.
-
Note that the full swing of the demodulated signal after a phase
flip equals two times the amplitude of the demodulated signal. The
conversion given is from peak-to-peak input signal to amplitude
of demodulated signal, not from peak-to-peak input signal to
full swing on phase flip.
Last updated May 14, 2001.