The Ramseyinterference pattern for a beam-clock, shown on the left, has a very wide fringe spacing. The atoms are hot and travel at thermal velocity (made into a beam by use of apertures), so the time between interrogations is short (in this case, about 5 milliseconds, or 5 one-thousandths of a second). The Ramsey interference fringes are only seen close to the resonance frequency (0 Hz difference between the microwave frequency and the Cesium atoms' natural oscillation frequency). The fringes "wash out" as the frequency is scanned away from the resonance because the atoms are hot and are travelling at different velocities, and so they have significantly different interrogation times. This means that the atoms being detected will have gone through a different number of oscillations depending on their speed and arrive with a different phase than the other atoms, canceling the interference signal.
In the same 200 Hz width of a single beam-clock fringe, we can see the entire Ramsey interference pattern for the fountain-clock. A single fringe is 100 times narrower, because the time between interrogations is 100 times longer. The Ramsey interference pattern is a much larger fraction of the overall signal width, because the atoms are cold, so the velocity of the atoms are very close to being the same value.