Microwave emission has been observed during the radial collapse, first compression and expansion phases of a dense plasma focus. The emission is broadband with the upper limit correlated inversely with the pinch radius. The maximum frequency of the emission was measured by use of the delay line technique and found to be most consistent with that of the lower hybrid frequency for the expected conditions. The inverse correlation of emission frequency with pinch radius can also be explained by this instability. Simultaneous measurements of the microwave and electron beam emission indicate that the two are not directly related.