Find peaks from spectrogram

Hey there.

I'm working with FSK generation and decoding. I currently have generated a signal containing 3 characters. These characters have been assigned different frequencies with my generator script.

I have made a spectrogram analysis of the signal:

Now I want to identify the different frequencies. I have tried everything from max, findpeaks etc. But when I convert my signal with the spectrogram function, I end up with entirely different frequencies and peaks. I have also made DFT analysis of my signal, but I end up with weird results. BTW. I have made a script that divided the signal into 3 parts (in this case of 1 second). Now I just need to find the dominant frequency during this time period.

Generator code:

function x = FSKgenerator(mysymbolseq, fstart, fend, Tsymbol, fs)

% fstart = 1000; % transmission band frequency start
% fend = 2000; % transmission band frequency end
% Tsymbol = 0.5; % symbol duration in seconds
% fs = 20000; % sampling frequency

farray = linspace(fstart, fend, 256); % 256 frequencies spread out in band
A = 1; % amplitude
n = 0:(round(Tsymbol*fs)-1);

myids = double(mysymbolseq); % convert 'abcd' to [97 98 99 100].. ie. 256 possible values

x = []; %empty array
for i=1:length(myids),
    myfreq = farray(myids(i)); % choose freq for current char
    sig = A*cos(2*pi*n*myfreq/fs); % create signal
    x = [x sig]; % add to full signal
end

Code for generating this signal:

clc, clear, close all

fstart = 1000; % transmission band frequency start
fend = 2000; % transmission band frequency end
Tsymbol = 1; % symbol duration in seconds
fs = 10000; % sampling frequency

signal = FSKgenerator('Hej', fstart, fend, Tsymbol, fs);

figure(1)
spectrogram(signal, hanning(1000), 0, 500, fs)

Answer 1

[Star Strider]

This is similar to locating DTMF tones. See for example How can i detect frequency of dtmf tone (.wav) file (link).

If you already know the tones you want to detect, see if the goertzel (link) function will do what you want.