1. NRAO Forty Foot Telescope Calibration using 3C392 Measurement: 10/30/2014
Author: Skip Crilly
GBO volunteer
First rev 11/6/2014
Rev 10/29/2018 to fix polarization issue and estimate Tsys given aperture eff. and measurement

2. Prediction of ΔTsys based on assumptions
3C392 flux = 171 Jy at 1420 MHz in two polarizations; unpolarized source assumption
Ref: Table in Forty Foot observer’s guide
RA 18h 53m 37s; Decl. +1deg 18m (1950.0) – Ref: P.R.R. Leslie - Observatory 80,23, 1960
Antenna aperture physical area calculated = 117 m^2
Aperture Efficiency is assumed to be 60% -> Effective Aperture = 70 m^2
Tsys is assumed to be 40 K
SNR 3C392 size is smaller (35mx27m) than antenna beamwidth FWHM (~1 deg)
Reference: Green’s Catalog - Cavendish Laboratory
Object Received Power: 171 Jy x 10^-26 (W/Hz m^2)/Jy * 70 m^2 = 1.20 x 10^-22 W/Hz
dBm/Hz in two polarizations ; dBm/Hz in each of two polarizations
Expected Receiver Noise Tsys = 40K: dBm/Hz -10*LOGBASE10(290 K /40 K) =
dBm/Hz
Single polarization Object Noise to Tsys Noise Power (dB) = dBm/Hz –( dBm/Hz) = -9.6 dB;
-9.6 dB -> 4.4 K increase in Antenna Sys. Temp is expected due to object measured in one polarization, assuming 40 K Tsys, and 70 m^2 effective area

3. Measurement +0.45 dB power measurement change when on and off object
Strip chart paper was left in the Forty Foot receiver room
Cross calibration of the dB increase used a dB resolution HP power meter compared to measured strip chart recorder pen movement.
This calibration could be improved; error estimated = dB
+0.45 dB to linear power ratio -> 10^(0.45/10) = ratio
1.109 ratio at 40 K Tsys corresponds to 4.4 K increase due to object

4. Conclusion
Estimate based on assumptions is that 3C392 will result in 4.4 K increase in assumed 40K dark sky antenna noise temp
3C392 was measured at 4.4 K increase in 40K assumed dark sky antenna noise temp
Aperture Efficiency and Tsys are “reasonably” close to estimates
Calculation and measurement error can be estimated more accurately
Better Tsys estimate and Aperture Efficiency can be researched
Additional work:
Additional sources can be checked
Check assumptions about Tsys and Aperture Efficiency
Improve strip chart calibration accuracy, i.e. cross-calibration
The other polarization measured approx. +-10% compared to the measured polarization
A&B Channels were manually matched to ~ +-10%
This should be followed up with improved calibration
Pointing issues
To Do – verify assumptions, check calculations and measurements