Check the pointing with crosses on the moon.

• an az strip (great circle) followed by n elevation strip.
• On 18,19 june the elevation strips were incorrect (i had the wrong offset coord in the script).
  
• each strip had 11 points covering -50 to +50 Amin in 10Amin steps
• At each point had 20 recs of 3 avg sweeps each.
• the horizons ephemeris was used to track the moon.

• 220618,19 az strip only
• 2.8 GHz hipass filter in, capton at 21.6 inches
  
• FF preamp on, attn=0
• 220621:  az and el strip
• 2.5 GHz hipass filter in, capton at 21.6 inches.
• FF preamp off, attn=0
• off moon, was close to noise floor of the FF

Processing the data:

    Try and exclude freq channels that have rfi when computing the total power.
    For each of the 11 points in a strip:

•  input the 20 spectra (each an avg of 3 sweeps).
• Compute a mask of good freq channels.
  
• compute the rms/mean by channel for the 20 spectra of a point.
  
• Do a robust linear fit to the rms/mean. Any fit residuals > 2.5 sigma were marked as bad.
• average the 20 spectra for the point

• exclude spectral points that stand out using a median filter
• for each of the 11 spcAvg of a strip:
• compute spcMed  = medianfilter(spcAvg) using a filter length of 120 freqChan (10001 total)
• divide :spcAvg/spcMed
  
• any freq channels > 1.2 are marked at bad

• create a single mask for the  strip combing the median filter mask with the rms/mean masks
• only use 2.8 to 10 GHz when computing the total power.
  
• for each point compute the total power using the good channels of the single mask

    Fit a Gaussian to each strip

•  Normalize the total power points of each strip by dividing by the average of the 2 endpoints of each strips (off the moon)
• fit to the function :
  
• z=(xoff - A1)/A2
• fit=A0*exp(-z^2/2) + A3 + A4*xoff
• where xoff are the offsets for the 11 points from the center of the moon.
• This fits the beam width convolved with the width of the moon (so A2 is not the beam width of the ant)

The plots show the results of the crosses on the moon (.ps) (.pdf):

•  Page 1: spectra off the moon.
• Top: 18,19 jun22.. az strips
• black: 18jun22, green : 19jun22
• 2.8GHz hipass filter in, preamp on, attn=0
• red: Noise floor of the FF. Above 10GHz the FF noise floor approaches the spectral values.
• Bottom: 21jun22 az an el strips
• Black: azstrip, green el strip
• 2.5 GHz hipass filter in, preamp off, attn =0
• red: noise floor of FF. It is within a few db of the off moon spectra.
• Page 2: Gaussian fits to the strips.
• Top: 18jun22  az strip it
• 2nd: 19jun22 az strip fit
• 3rd:  21jun22 az strip fit (preamp off)
• bottom: 21jun22 el strips fit (preamp off)

Fit values:

Summary

• The moon deflection of .41 Tsys
• the average az pntOffset was:-1.1 Amin
• the el pnt offset was: 2.53 Amin
• Adding them in quadrature gives a pointing error of 2.7amin
• This is computer over 2.8 to 10 GHz.
• the beam width probably varies from 40Amin to 9amin, with most of the power probably coming at the lower end.
• This pointing error means that we can use the position switch  patterns without worrying about large pointing errors.

processing: x101/220621/crosses.pro

Tsys using on,off the moon.

• 220617: 2 on,off position switches done.
• 220620: 1 on,off position switch done.
• capton at 21.6 inches, 2.8 GHz hipass filter in, FF preamp in, attn=0
• The horizons ephmerides were used to track the moon center
• the off position was 10Min Time. With a dec of -24deg, this was a great circle offset of about 137 Amin.
  

Processing:

• The off
  
• The 20 spectra for each on,off were averaged.
• Tsys was computed as:
• (on-off) = moon Deflection
• off         = Tsys deflection
• MoonDefl/TsysDefl= (on-off)/off = (on/off -1)
• TsysDefl=MoonDefl/(on/off -1)
• If no size correction then MoonDefl=Tmoon.
  
• TsysK=Tmoon*sizeCor/(on/off - 1)
• The sizeCor was an attempt to  correct for the extended beam on the moon.
• The  moon is taken as a constant brightness temperature of 220K.
• The beam  will spill off the moon (sidelobes at lower freq, main beam+sidelobes at lower freq.)
• The temperature increase caused by the moon will decrease as the spill over increases.
• The plot shows a means to correct for this (.pdf)
• The curves show the decrease in temp as a function of the ration of HPBW/diameterObect and by the pointing offset as a fraction of the angular radius.
• I used the pointing offset measured by the crosses on the moon: 2.7Amin
• 2.7/15Aminmoonradius=.18
• The blue line shows the pointing error that was used.
• The curves only go down to  hpbw/diamthobject=1.
  
• unfortunately our hpbw/30amin goes to 1.3 ..
• instead of computing the convolutions to this extent. i just eyeballed and extrapolated the .9->1.0 step
• So the lower freq correction has been fudged.
  
• The page is taken from the paper by Ho et al (.pdf)
  

The plots show the results of the on,offs (.ps) (.pdf)

• Page 1:17jun22. 2 on,off spectra
  
• Top: spectra on,off moon
• black: on moon (2 spectra over plotted)
• red : off moon (2 spectra over plotted)
• middle: on/off -1
  
• The spectra has been smoothed to 31 MHz.
  
• black: 2 patterns over plotted.
• red:  average of 2 patterns
• bottom: Tsys  vs frequency (with no size correction)
• the blue line is 500K
• This assumes that  the moon 220K temp fills the beam and the sidelobes
• Page 2: 20jun22 on,off on moon (1 pattern)
• the 3 frames are the same as page 1 (except only 1 pattern.
• Page 3:try to correct for the beam size
• Top: Tsys vs freq with no size correction.
• black is the average of the 2 17jun22 measurements
• red is the 20jun22 measurement
• Middle: computed correction factor for the beam size
• This was taken for the figure in the Ho paper
• I used 2.7 amin as the pointing error
• fwhm=1.02*lambda/D=12  was used for the beam widths
  
• I also extrapolated to  ratios > 1.
• Bottom: Tsys vs freq after size correction
• i average the 3 on/off values and then applied the sizeCor in frame 2 to Tmoon.
• The dashed lines are at 200,300,400, and 500 Kelvins.
• Their is still lots of rfi in the plot
• 5-6GHz is the uni band

Summary:

• on,offs on the moon were used to compute the Tsys for the QRFH on the 12meter
• 220K was used for the moon's brightness temp over 2 to 12 GHz
• a   size correction was used to decrease Tmoon seen by the system.
• the lower freq correction was extrapolated. It not as reliable as the higher freq correction.
• Tsys goes from 200K at 3GHz to  > 500K at 10GHz.
• These values are larger that those measured using the absorber  and sky yfactor measurements.
• When computing the size correction i should have used a beam map with the sidelobes and all (but one was not available with this horn.)
  
• For the Yfactor values I  used Tflange   + Tscattered + Tsky=10K
  

• Tsys values

  Measurement	3-3.5 GHz	8-8.5 GHz	10-10.5 GHz
  Moon	230K	430K	600K
  yfactor sky,abs	202K	245K	393K

  
  

SEFD using CasA

• The absolute spectrum of Cas A: baars, et al 1977 (.pdf)
• The flux was corrected to 2022.
• An accurate flux density scale 50 to 50GHz. perley et al, 2017 (.pdf) (with no correction to 2022).
• they claim the casA fit good to 4 GHz although the plots look pretty good to higher freq. This limitation may have been because of the interferometer beam size.

The plots show the on,off spectra and sefd: (.pdf)

• Page 1: on, off spectra
• Black is the  average of the 4 on source spectra
• red is the average of the 4 off source spectra.
• Purple is the noise floor of the FF.
• Page 2: on/off, flux and sefd
• top: on/off -1
• black are the 4 on/offs-1 over plotted
• red is the average of the 4.
• middle: casA flux
• black: baars flux
• red : Perley flux
• The solid line are the standard values.
• The dashed lines are corrections to the flux because CasA is extended
• the extended source correction: (fwhm^2)/(fwhm^2 + srcWidth^2)
• is used 5 amin for casA width
• fwhn came from 1.02*lambda/Diam
• bottom: sefd
• The SEFD= Tsys/Gain
• on/off -1 = casADeflection/TsysDeflection
• casADeflection= fluxCasA*gain(k/Jy)
• sefd= TsysDeflection/casADeflection/fluxCasA=fluxcasa/(on/off -1)
• I've used the corrected flux (frame 2)
• black i baars flux
• red in perley flux.
• The data was smoothed to 31 MHz.
• Page 3: compute sefd in 500 MHz bw steps.
• Top: casA srcDeflection/Tsys in 1 500 MHz steps
• rfi channels were  excluded by:
• using robust fits to the rms/mean by chan
• and dividing by a median filtered spectra and clipping at 1.2 Tsys.
• Middle : sefd for the 500MHz totpwr pnts
• black used the baars corrected flux.
• red is the Perley corrected flux
• there is lots of rfi between 5 and 6 GHz (UNI band).
• bottom:  aperture efficiency for various Tsys values.
• The aperture efficiency is Tsys/SEFD*2760/(PI*DIAM/2)^2
• A gain of 1 K/Jy  has 2760 m^2 (apertureEff=1=1.)
• The different colors are the efficiencies for various Tsys values

Using the tsys measured with the moon on,offs and the sky absorber measurements give the following aperture efficiencies:

    The efficiency from the moonTsys is giving an efficiency that is higher than expected. The probably means the moon Tsys is too high.

On off position switch on sun

    On 17jun22 we did 2 on off position switches on the sun. the setup was:

• qrfh at 21.6" from secondary
• horn->lna->biasT->4ft cable->biasT->2.8ghz Hipassfilter->field fox
• fieldfox, 0db attn, pre amp on. rbw 1Mhz,avg 3 sweeps\
• 20 recs on, 20 recs off source
• off source was 137 amin (great circle).

The plots show the on,off position switch results (.ps) (.pdf)

• Page 1: on,off spectra
• Top: on sun, off sun spectra
• Black in on sun, red is off sun, purple is the noise floor of the field fox
• all of these have been moved to the output levels of the horn.
• two on,offs have been over plotted.
• Bottom:  (on-off)/off (sun deflection in units of Tsys)
• black: 2 patterns overplotted
• red: average of 2 patterns
• blue: average smoothed to 31 MHz.
• The dips are rfi in the off spectra.
• Page 2: computed temp of the sun
• A model for the sun temperature was used:
  
• Tsun=A*freqGhz^(-2.1) + Tchromosphere
• Blackline: A=140077K , Tchrome=10880 
  
• Red line: force Tsun to be 9000K at 8.5GHz
• This is a typical value have been measuring with the12meter solar maps.
• Tsys in degK using the deflection on the sun and the above models.
• This 100% coupling between the incoming radiation and the 12m output (itexcludes the aperture efficiency.
• Page 3: Solar power vs freq
• use the 2 previous models
• the freq channels are 1Mhz rbw
• The total integrated power is about -57 dbm
• The cryo elec lna's for the new system will have a 1db compression of -35dbm.
  

Were we pointing at the sun?

    On 18jun22 a cross was done on the sun (but only the azimuth strip was valid. The setup was:

• horn,field fox same setup as 220617 above
• the azimuth strip was -50 to +50 arcminutes (great circle) with 11 10Amin steps
• each point:
• average 3 sweeps/rec then average 10 recs.

The plots show the azimuth strip results (.ps) (.pdf)

• top: average spectra for the 11 points across the azimuth strip
• each color is a different point.
• The power levels has been translated to the output of the qrfh
• Bottom: Total power vs az strip offset
• Each * is one of the 11 points
• The vertical scale has been normalized to the value at the strip edges (tsys).
• The actual peak is probably 5amin offset from the expected center.

    The pointing error of 5amin --> that the total power computation on 17jun22 is probably not biased by pointing errors.

processing: x101/220618/suncross.pro