Oblique propagation traces observed by an airborne ionosonde at different ranges from the Platteville heater facility during a period of overdense heating have been simulated by using a representative ionospheric model and standard ray-tracing techniques. The heater frequency used during the time discussed in this paper was 6.2 MHz, while f0 F2 was approximately 8 MHz. The plasma frequency of 6.2 MHz was deduced to occur at approximately 260-km altitude. The simulated ionograms are found to reproduce accurately the main features of the observed ionograms, over a wide range of ionosonde to heater distances. Comparison of the simulated and observed ionograms indicates that the irregularities created by the heater existed at altitudes of 200 to at least 280 km, over an area of radius approximately 100 km.