Jamming in Czechoslovakia. “RFE/RL Research”: “Before the invasion of Czechoslovakia this language service was jammed by stations both inside and outside the country. The latter are in the USSR. On May 8, 1968 Czechoslovakia had stopped all jamming except for some transmissions of RFE. Immediately after the [Soviet] invasion and for several days thereafter there seemed to be some confusion among the jamming networks and some of the lower frequencies we used for Czechoslovak were free of jamming. What jamming there was on the higher frequencies then seemed to be by jammers in the USSR, and for a while the medium and lower short-wave frequencies were quite clear of jamming. This situation changed about the beginning of September 1968 when [...] the former jammers located in Czechoslovakia made a slow comeback: the old call sign “Z3” was first heard again on 25 November, 1968 and “G7” reappeared on 7 January 1969. A new stronger jammer started on [medium wave] 719 kc on 25 March 1969. In summary, all Czechoslovak frequencies are now heavily jammed from the USSR and Hungary, and from within Czechoslovakia. Jamming against the RFE Czechoslovak service has varied over the years, but can in general be characterised as heavy noise jamming”. There were 18 local town jammers in Czechoslovakia. Three sky wave jamming radio stations transmitted interference to the USSR and Bulgaria.