In September 1983 VHF plasma line backscatter was obtained at Kiruna, Sweden, from the ionosphere illuminated by strong HF radiation from the German-Norwegian heating facility located near Tromso, Norway. The downshifted plasma line was observed during two periods when the heater operated on a frequency that was lower than critical. The plasma line was never observed earlier than about 15 s after heater turn-on and the intensity was very variable in time. A plausible assumption is therefore that the plasma line scattering observed is caused by Langmuir waves generated by direct conversion of the heating wave due to interactions with striations built up slowly in the modified ionospheric region.