Beijing: More than 500 sets of equipment for making unauthorised radio broadcasts were seized in China over the past six months in a national campaign aided by more than 30,000 airwave monitors, the media reported on Thursday. The campaign, launched on February 15 by the State Council, resulted in 1,796 cases related to illegal radio stations, after 301,840 hours of monitoring from February to July, according to an online statement by the Ministry of Industry and Information Technology. The number of incidents was down by 50 per cent from April to August, the China Daily quoted the statement as saying. So-called pirate radios have appeared in most parts of China since 2015 and this "has been a channel for criminals to defraud and promote aphrodisiacs, along with counterfeit and poor-quality medicine", according to the Ministry of Public Security's Criminal Investigation Department. The operating cost of a pirate radio is low, but profit can be high. A pirate radio station that broadcasts advertisements for aphrodisiacs can pocket more than 70,000 yuan ($10,500) a month, with an overhead cost of no more than 10,000 yuan, investigators said in a post on Sina Weibo. It said most spare parts for broadcasting equipment can be bought on the internet. "The broadcast power of pirate radio stations can be 2,500 to 5,000 watts, which is several hundred of times that of commercial radio, and the signal can be received 300 km away," the China Daily reported citing the department as saying. Pirate radios may also pose a threat to communication between aircraft pilots and ground controllers as their frequency band neighbours that of flight navigation signals and can create interference, the department said. Under Chinese law, the unauthorised use of radio frequency bands can attract up to seven years in prison.