Tsys using sky and absorber
Sensitivity using crosses from dipole 1.
Summary

    The sensitivity of the byu system was measured using a single dipole fed down to the AO iflo system and recorded on the interim correlator. Crosses on continuum sources as well as temperature measurements using sky and absorber.

---

Tsys using sky and absorber:

    On 26aug10 Tsys was measured using sky and absorber. The setup was:

• data taken with the dual pol array in position A0, focus=0.
  
• polA dipole 1 and polB dipole 2 were recorded.
• The interim correlator recorded 1.25 MHz bw at 1612. 15 1 second integrations at each position were taken.
  
• The sequence was:
• on sky for 15 secs
• move turret, mount absorber
• on absorber 3*15 secs. absorber temp = 84.5F
• dismount absorber, move to tertiary, take 2*15 seconds more of data.

Processing the data:

• Each 15 second integration was average over time and frequency.
• The data was recorded in correlator units (linear in power). No cal diode was available.
  

Analyzing the data:

• Tabs the absorber temp
• Trcv the receiver temp (including the dipole)
• Tspill the tertiary spillover and any scattered energy off the platform.
• Tsky  the power from the sky.
• _C       power in correlator counts
• _K       power in degK
  

• deltaT_C=Thot_C -Tcold_C = (Tabs_C + Trcv_C) - (Tsky_C + Tspill_C + Trcv_C)= Tabs_C - (Tspill_C + Tsky_C)
• We measured Tabs_K (302 K) with a thermometer.
  
•  To convert Correlator counts to Kelvins:
• Using Thot: we measured Tabs_K, estimate Trcv_K, we measured Thot_C
  
• CorToKelvins= (302.3K + Trcv_K)/Thot_C
• Once we have CorTokelvins we can then compute the Tsky_K+Tspill_K:
• (Tsky_K + Tspill_K)=(Tabs_K - deltaT_C*CorToKelvins
  

    The plot shows the Hot,cold measurement (.ps) (.pdf):

• Top: this shows the ratio Thot/Tcold for the 3 measurements it was relatively stable.
• the black line is dipole 1 polA, the red line is dipole 2 polB
  
• Bottom: Tsky + Tspillover in kelvins vs Trcv in kelvins.
• A guess at TrcvK would be 45 K (32K from the amps and 13K from lines and dipoles)
• This gives Tsky+Tspill
  
• dipole1: Tspill + Tsky = 53 K
• dipole2: Tspill + Tsky = 60 K
• You might expect Tspill dipole 2 to be larger since it is offsets from the paraxial ray.
• Tsys for dipole 1 would be : 53 + 45 = 98K.

    These measurements used a single dipole. The phased array feed will have different values.

processing: x101/100831/absorber.pro

---

Sensitivity measurements using crosses on dipole 1.

    Crosses were done on continuum sources using dipole 1

The cross setup was:

• +/- 3 beam widths in azimuth followed by +/- 3 beam widths in za.
  
• Each leg of the cross took 60 seconds with 1 hz sampling.
• the interim correlator sampled 1.5625 MHz centered at 1612 MHz.
• Crosses were done a the various positioner sites: A0 .. A6
• Most   crosses were done at focus = 0 cm. (about 10 crosses (out of 144) were done at focus=-8 cm.
• the data was taken in jun10 and aug10 using the single pol array.

Processing the data

• 2-d gauss fits were done to each cross:
• Fit for: The Tsys offset, Gaussian amplitude, x,y offsets, major, minor axis widths, and ellipse rotation angle.
  
• 122 crosses were done in total.
• No cal was available so the SEFD  (Tsys/Gain) was computed.
• As we moved away from the central position A0, the beams become less Gaussian due to the coma. lobes.
  

The first plots show the strip data with the fits overplotted for 7 crosses done on A0..A6 (.ps) (.pdf)

• Black in the az strip, red is the za strip, and green is the 2d fit
• positions A0-A6 are shown. These 7 strips were taken on 19aug10 with the single pol array.
  

The next set of plots   show the results of all the fits (.ps) (.pdf):

• Page 1 top: SEFD  in janskies versus za for the 122 crosses.
• The different beam positions are color coded.
• The dotted lines are the median SEFD  for each position.
• The outer positions have larger SEFD's
• Page 1 bottom: Ae/Tsys: effective area/Tsys
• Ae/Tsys=2760*gain/Tsys=2760./SEFD.
• This is the value plotted in most of karls sensitivity maps.
• Page 2: average SEFD and Ae/Tsys for each position
• Top is the sefd, bottom is the Ae/Tsys
• Black  is the mean , red is the median.
• Page 3: beam widths vs za.
• Top has the beam widths for each cross.
•  * is the major axis beam width
• + is the minor axis beam width.
• the color coding are the positions A0 .. A6
• The units are Arc seconds
• Bottom: The average beam widths for each position.
• * black is the average for the major axis
• + red is the average for the minor axis
• * green is the average of the two.
• The  outer positions beam widths are distorted by the coma.
• Page 4: major, minor axis lengths
  
• The beam widths measured were plugged into germans approximations for the major,minor axis for an ellipse
• black is the major axis, red is the minor axis, and green is the average.
• the axis lengths for the outer beams look a bit suspicious (since the tertiary can't illuminate 300 meters).
• this is coming from the coma messing up the beam width fits for the out beams.
• The lengths are larger than  the expected: 237x207.
• position A0 has a major axis mean length of 250 meters (using germans approximation).
  
• For the single pixel receivers, the hpbw's were measured back in 2004-2005 
• Using  hpbw=1.02*lambda/DiamEffective gave a typical diameter of 225 Meters (depending on the horn taper).
  
• Using the mean bandwidth of dipole1 = 160 Asecs beam width
• diamEffective=240 meters.
  
• This is close to the 235 meters measured for the 610 MHz dipole.
  
• The horns have a taper on the tertiary around 15-18 db and a 9 db taper on the edge of the illuminated area (i wonder how the illuminated area was defined to get this 9db value... need to ask lynn baker).y
• To get an idea for the single dipole illumination of the tertiary,  I took a horzontal 1/2 wave dipole lambda/4 above a ground plane (Kraus antennas pg 461.)
• The plot shows the dipole illumination pattern (.ps) (.pdf)
  
• At the edge of the tertiary (60 deg) there is a 6db taper in the power pattern (assuming i didn't mess something up copying the equation.
• This taper should give a more uniform illumination of the primary than the horn feeds. So you would expect a smaller bandwidth.
  

processing: x101/projects/byuPhAr/idl/cross/byusefd.pro, x101/projects/byuPhAr/test/spillover,

---

Summary:

• Conclusions are for the single dipole at A0 (unless other wise stated).
• The paf will have different results since they can play with phasing the various dipoles to create a beam.
• Note: 2760 m^2=1 K/Jy.
  

Measurement	value	Notes
Tspillover +  Tsky	Dipole1:53k, dipole2:60k	Assumes Trcv =45K
Tsys	100 K	Assumes Trcv=45k
SEFD	11 Jy	Only relies on the source flux (and the 2d fit).
Ae/Tsys	251  m^2/K	just  2760/SEFD
Ae from Ae/Tsys and Tsys	25100 m^2	assumes Trcv=45K, Tsys=100K
A_eff/A_geom	25100/38500=65%	This will increase as Tsys goes up the geometric area is from german's "last ray) over the tertiary .
Beam widths	major axis: 150 asecs minor axis: 170 asecs avg:            160 asecs	The avg bw is smaller than the lbw receiver at 1610 MHz: 178 asecs
taper at tertiary edge	dipole:6 db horns:15-17db	Using 1/2 lambda dipole lambda/4 above ground plane from kraus. this compares with the 15-17 db tertiary edge taper for the single pixel horns The smaller edge tape should give a narrower beam width for the dipole.