Find a signal xt that could have produced the spectrogram sh

Find a signal x(t) that could have produced the spectrogram shown in the figure below.

clear all;

close all;

clc;

t=0:0.05:2*pi;

f=0:50:400;

x=sin(2*pi*f*t);

subplot(2,1,1);

plot(t,x);

xlabel(\'time in seconds\');

ylabel(\'frequence in HZ\');

title(\'original signal\');