Zinterp=rmarker1(Z,Freq,Zo,Markers,Mnumber)

function Zinterp=rmarker1(Z,Freq,Zo,Markers,Mnumber)
% Return Loss Marker
%
% Draws a single marker on Return Loss plot at frequency specified
% by Marker. Returning the interpolated Z value. It allows 
% individual markers to be applied to different impedance plots.
%
% Usage: Zinterp=rmarker1(Z,Freq,Zo,Marker,Mnumber)
%
% Z........Impedance vector (Ohms)
% Freq.....Frequency list (MHz)
% Zo.......Characteristic impedance (Ohms)
% Marker...Marker frequency (MHz)
% Mnumber..Marker number 1-8
%
% e.g. vswrc(Z,Freq,Zo);
%      rmarker1(Z,Freq,Zo,880,1)
%      rmarker1(Zin,Freq,Zo,880,2)

% N.Tucker www.activefrance.com 2008


axis('square');

[RowF,ColF]=size(Freq);
[RowZ,ColZ]=size(Z);
[RowM,ColM]=size(Markers);

if ColZ>ColF
 Z=Z(1,1:ColF);
end

index=zeros(1,ColM);
interp=zeros(1,ColM);

M=1;
if Markers(M)<=min(Freq),
  Markers(M)=Freq(1,1);
 end
 if Markers(M)>=max(Freq),
  Markers(M)=Freq(1,ColF)-0.0001;
 end


M=1;
for N=2:ColF,         % Loop thru freqs
   if (Markers(M)>=Freq(N-1)) & (Markers(M)<Freq(N)),
   index(M)=N;
   end
  end

  M=1;
  F2=Freq(index(M));
  F1=Freq(index(M)-1);
  interp=(Markers(M)-F1)./(F2-F1);
  Z2=Z(index(M));
  Z1=Z(index(M)-1);
  Ymarker(M)=Z1+interp.*(Z2-Z1);

Xmarker=Markers;
Zinterp=Ymarker;


hold on;
Zr=Ymarker;
p=(Zr-Zo)./(Zr+Zo);
s=(1+abs(p))./(1-abs(p));
R1=real(20.*log10(p));
plot(Xmarker,R1,'+','color','k','LineWidth',2);

RHSx=0.88;  % Marker text position for markers on RHS
LHSx=-0.28; % Marker text position for markers on LHS


% Markers 1-4 RHS

I=1;
 t=sprintf(' %g',Mnumber);
 text(Xmarker(I),R1(I),t,'FontWeight','bold');

if Mnumber==1
 t1=sprintf('1) %g Mhz',Markers(1));
 t1a=sprintf('%5.2f dB',real(R1(1)));
 textsc(RHSx,.90,t1);
 textsc(RHSx,.85,t1a);
end


if Mnumber==2
 t2=sprintf('2) %g Mhz',Markers(1));
 t2a=sprintf('%5.2f dB',real(R1(1)));
 textsc(RHSx,.70,t2);
 textsc(RHSx,.65,t2a);
end

if Mnumber==3
 t3=sprintf('3) %g Mhz',Markers(1));
 t3a=sprintf('%5.2f dB',real(R1(1)));
 textsc(RHSx,.50,t3);
 textsc(RHSx,.45,t3a);
end

if Mnumber==4
 t4=sprintf('4) %g Mhz',Markers(1));
 t4a=sprintf('%5.2f dB',real(R1(1)));
 textsc(RHSx,.30,t4);
 textsc(RHSx,.25,t4a);
end

% Markers 5-8 LHS

if Mnumber==5
 t1=sprintf('5) %g Mhz',Markers(1));
 t1a=sprintf('%5.2f dB',real(R1(1)));
 textsc(LHSx,.90,t1);
 textsc(LHSx,.85,t1a);
end


if Mnumber==6
 t2=sprintf('6) %g Mhz',Markers(1));
 t2a=sprintf('%5.2f dB',real(R1(1)));
 textsc(LHSx,.70,t2);
 textsc(LHSx,.65,t2a);
end

if Mnumber==7
 t3=sprintf('7) %g Mhz',Markers(1));
 t3a=sprintf('%5.2f dB',real(R1(1)));
 textsc(LHSx,.50,t3);
 textsc(LHSx,.45,t3a);
end



if Mnumber==8
 t4=sprintf('8) %g Mhz',Markers(1));
 t4a=sprintf('%5.2f dB',real(R1(1)));
 textsc(LHSx,.30,t4);
 textsc(LHSx,.25,t4a);
end


hold off;