Vertical Incidence Skywave (NVIS), the most commonly used technique capable of providing seamless local-to-medium distance HF communications. Information about the Critical Frequency (foF2) of the ionosphere at any one time is highly important for setting up and maintaining reliable NVIS radio links. This information can be found online from ionograms produced by local ionosondes at this site Propagation beacons A number of amateur radio propagation beacons are active on 5 MHz, some of which produce a sequence of varying power levels in various transmission formats. A number of these transmit 24/7 (but not all) and some personal beacons are activated as required. In the United Kingdom (ITU Region 1) Only GB3ORK (Orkneys IO89ka) is now active on 5290 kHz. The timing of the transmission is every 15 minutes starting at 2 minutes after the hour ( i.e. 02, 17, 32 and 47 minutes ). GB3ORK transmits a JT9A sequence in addition to stepped power levels. Originally three beacons transmitted sequentially on the hour and each subsequent 15 minutes primarily using CW. They were in transmission order GB3RAL, GB3WES and GB3ORK, from approximately southern, central and northern locations in the UK respectively. GB3WES closed down on March 11, 2020, when its Notice of Variation (i.e. licence) expired and in July 2017, the licence for 5 MHz operation of the southern beacon GB3RAL was not renewed owing to site difficulties. Details of the original British beacon network, including design and building, can be found on the 5 MHz beacon page of the Radio Society of Great Britain (RSGB) website. On the 5290 kHz channel (5289.5 kHz USB) also is the Danish (ITU Region 1) personal beacon OV1BCN (JO55si), operated by OZ1FJB, particularly for NVIS observations. From Spring 2011, it has been in operation h24 and is sequenced to transmit 2 minutes after the UK beacons, (hr+ 04/19/34/49 min.), transmitting a USB-announcement, followed by CW + MT63 identifications. (Info: Lars, OZ1FJB) The South African Amateur Radio League SARL (ITU Region 1) As of May 2017, the South African 5 MHz WSPR Cluster has two permanent beacons currently ZS6SRL in Johannesburg (KG33wv) and ZS1OA (JF95fx) in Cape Town. Although no longer operational, when SARL first announced its intention to have a 5 MHz Beacon operational, the South African club KARTS Kempton Park Amateur Radio and Technical Society commissioned a WSPR beacon callsign ZS6KTS (KG43cw), initially on 5250 kHz. At a meeting during Summer 2014