Loss cone distribution have, until recently, been considered the prime cause of odd-half cyclotron harmonic emissions. On the basis of new observations, it has been proposed that shell-Maxwellian distributions are also unstable to these modes. To test this model, we have designed a laboratory experiment where a shell-Maxwellian distribution is produced. Analysis of the plasma noise spectrum shows that the emissions fall within the cyclotron harmonic branches (Bernstein waves). Test wave dispersion analysis, spectral correlation measurements, and real time observations indicate that our plasma, which has the upper hybrid resonance in the first Bernstein wave branch (&ohgr;uh/&ohgr;ce =1.8), exhibits a nonconvective (absolute) instability at &ohgr;/&ohgr;ce =1.3, in contrast to the predictions of loss cone theory for the upper hybrid branch. In addition, the test wave dispersion relation of the plasma reveals that below the instability frequency the system behaves as if it were composed of shell electrons only. Present theories do not account for these findings.