is any synchronization required for converting bandpass modulated signal to passband modulated signal

i have written this code which up converts baseband fsk modulated signal to passband then down convert it to baseband then demodulates it. ideally there should be zero bit error rate but it is close to 0.5. could anybody suggest something. i will be really thankfull. code is attached below....

clc
clear
fs=6e7;

x=randint(10,1);
mod=fskmod(x,2,500,7,fs);
hDUC = dsp.DigitalUpConverter;

      % Up convert the signal and visualize the spectrum
      xUp = step(hDUC,mod); % up convert
      hDDCMinOrder = dsp.DigitalDownConverter;
      % down convert the signal and visualize the spectrum
      xdown = step(hDDCMinOrder, xUp); % downgoogl convert
      demod=fskdemod(xdown,2,500,7,fs);
      [num,rate]=biterr(demod,x)

S = fft(mod);
S = abs(S(1:round(length(mod)/2)+1));
frqS = [0:length(S)-1]*fs/length(mod);
figure
plot(frqS,S) 
title('Spectrum of modulated Signal')
xlabel('Frequency (Hz)')
ylabel('Amplitude')

S = fft(xUp);
S = abs(S(1:round(length(xUp)/2)+1));
frqS = [0:length(S)-1]*fs/length(xUp);
figure
plot(frqS,S) 
title('Spectrum of upcon Signal')
xlabel('Frequency (Hz)')
ylabel('Amplitude')

S = fft(xdown);
S = abs(S(1:round(length(xdown)/2)+1));
frqS = [0:length(S)-1]*fs/length(xdown);

figure
plot(frqS,S) 
title('Spectrum of downcon Signal')
xlabel('Frequency (Hz)')
ylabel('Amplitude')