calibrate_linearity

 d = calibrate_linearity(d)

 This function uses the measured detector diode curves to correct for the
 non-linearity of the detector diodes.

 To look at the linearity of the data --> convert switchData to Volts then
 into power using the measured diode response. Then convert back to
 digital units, because some functions (namely passband functions) expect
 units in digital units.

 OGK and ACT, July 2011

0001 function d = calibrate_linearity(d)
0002 % d = calibrate_linearity(d)
0003 %
0004 % This function uses the measured detector diode curves to correct for the
0005 % non-linearity of the detector diodes.
0006 %
0007 % To look at the linearity of the data --> convert switchData to Volts then
0008 % into power using the measured diode response. Then convert back to
0009 % digital units, because some functions (namely passband functions) expect
0010 % units in digital units.
0011 %
0012 % OGK and ACT, July 2011
0013 %
0014 
0015 
0016 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0017 % Diode curves as measured by Oliver
0018 % Best fit quadratics:
0019 %
0020 % Input power (mW) = D(1).*x^2 + D(2)*x + D(3)
0021 %
0022 %  where x is ouput voltage in V
0023 %
0024 %  D is the array of polynomial coefficaient D[12,1:3]
0025 %  For diodes 1 to 12  with 3 coefficients each
0026 %
0027 %%%%%%%%%%%%%%%%%%%%%%%%%%
0028 
0029 D(1,1:3) = [ 18.480 1.285 0.000];
0030 D(2,1:3) = [ 17.395 1.244 0.000];
0031 D(3,1:3) = [ 17.954 1.252 0.000];
0032 D(4,1:3) = [ 17.501 1.251 0.000];
0033 D(5,1:3) = [ 19.851 1.391 0.000];
0034 D(6,1:3) = [ 17.264 1.236 0.000];
0035 D(7,1:3) = [ 18.786 1.309 0.000];
0036 D(8,1:3) = [ 17.384 1.251 0.000];
0037 D(9,1:3) = [ 18.208 1.266 0.000];
0038 D(10,1:3) = [ 17.357 1.211 0.000];
0039 D(11,1:3) = [ 17.444 1.217 0.000];
0040 D(12,1:3) = [ 16.289 1.258 0.000];
0041 
0042 % The average diode has linear slope, used to convert the non-linearity
0043 % corrected power back to a voltage.
0044 % See wiki page http://astrowiki.physics.ox.ac.uk/CBass/DetectorDiode
0045 V2mW = 1.289; % mW/V
0046 
0047 % Convert switchData from Backend units to Volts
0048 % To account of the gain of readout and filter board we have a factor of
0049 % 6.5 in the equation, which is the gain of the backend board.
0050 % 4999 digital units corresponds to an input voltage of +1.25V
0051 % Therefore the conversion factor is:
0052 BU2V = 1.25./((10^4)/2)/6.5; % V/DU
0053 
0054 d.antenna0.receiver.switchData = d.antenna0.receiver.switchData*BU2V;
0055 
0056 % Now use diode calibration curves to go from V to mW input power
0057 % Diodes are in pairs for the 24 channels
0058 % Preallocate power array
0059 P = ones(size(d.antenna0.receiver.switchData));
0060 
0061 for i=1:12
0062     %first channel with this diode
0063     V = d.antenna0.receiver.switchData(:,(2*i)-1);
0064     P(:,(2*i)-1) = ( (D(i,1)*V.^2) + (D(i,2)*V) + D(i,3) );
0065     clear V
0066     % second channel with this diode
0067     V = d.antenna0.receiver.switchData(:,(2*i));
0068     P(:,(2*i)) = ( (D(i,1)*V.^2) + (D(i,2)*V) + D(i,3));
0069     clear V
0070 end
0071 
0072 % go back to digital units
0073 P = P/V2mW/BU2V;
0074 d.antenna0.receiver.switchData = P;
0075 
0076 clear P
0077 
0078 end