function [freq,signal]=HPpower(filename);
%
% Read in power spectra files which have been saved on the HP3536A and converted to
% PC-readable format by 63x_mx.bat from the /lifutil folder on Bob's Desktop.  
% 
% returns freq = array of frequencies measured at
%         signal = power spectrum, in Volts(rms)
%
% data will NOT be normalised by root Hz if 63x_mx.bat was used.  
%
% (Modified by Dave Bonfield from HPread.m, which was supplied by AJW)
%
fid = fopen(filename,'r');
%
% three header lines, which contain the # of data points:
t1 = fgetl(fid);
t2 = fgetl(fid);
t3 = fgetl(fid);
[q1 N q3 q4] = strread(t3,'%s%d%d%s');
%
% "N" should now be the number of data points measured
%
% Now read in the frequencies measured at
freq = fscanf(fid,'%f');

% now a comment line, also containing the # of data points:
t4 = fgetl(fid);
[q1 N q3 q4] = strread(t4,'%s%d%d%s');
%
% now the signal - in whatever units the batch file used for conversion has made them
% - for 63x_mx.bat this seems to be unnormalised, i.e. NOT per root Hz, Volts(rms).  
signal = fscanf(fid,'%f', N);
%
% close the file:
fclose(fid);
% return;