based on their age and gender. Only the M21 category must locate all five transmitters, while the other categories may skip only a specified transmitter or transmitters. M19—Men ages 19 and younger, 4 or 5 transmitters M21—Men of any age, 5 transmitters M40—Men ages 40 and older, 4 or 5 transmitters M50—Men ages 50 and older, 4 or 5 transmitters M60—Men ages 60 and older, 3 or 4 transmitters M70—Men ages 70 and older, 3 or 4 transmitters W19—Women ages 19 and younger, 4 or 5 transmitters W21—Women of any age, 4 or 5 transmitters W35—Women ages 35 and older, 4 or 5 transmitters W45—Women ages 45 and older, 3 or 4 transmitters W55—Women ages 55 and older, 3 or 4 transmitters W65—Women ages 65 and older, 3 or 4 transmitters Youth competitions The International Amateur Radio Union rules for ARDF competitions include provisions for youth competitions. These competitions are restricted to competitors aged sixteen years or younger. The course lengths are shorter (up to six kilometers), the transmitters may be located closer to the start (500 meters), and a course setter may require that fewer transmitters be located. Since 2017, there is World Youth ARDF Championship (WYAC) every year. Participating categories in these championships are W14, W16, M14 and M16. WYAC by year 2017 - Turcianske Teplice, Slovakia 2018 - Doksy, Czech Republic 2019 - Vinnytsia, Ukraine Local variations The IARU rules go into great detail about certain procedures that are unique to international championships events. Not every ARDF competition follows all of these rules. Common variations to the generally accepted rules exist at local events. Most smaller events do not have large juries or on-course referees. Some events will use simpler start procedures, such as using only one starting corridor instead of two. ARDF events on the two meter band in North America sometimes use frequency modulation instead of amplitude modulation for the transmission of the Morse code identifications. Map and course details Ideally, the topographic maps used in ARDF competitions are created using the International Specification for Orienteering Maps 2000 (ISOM) set by the International Orienteering Federation and used for orienteering competitions. In fact, many ARDF competitions use existing orienteering maps, in collaboration with the orienteering clubs that created those maps. Course design is an important element of a successful competition. The international rules adopted by the IARU include both requirements and recommendations for basic course design.