The Cocos Islands Ionosonde station in Cocos Islands, WA, Australia, has Ionosondes since November 1961. According to the SWS archived Cocos Islands scaled ionospheric data book (Series D), there was an Cossor 7562C ionosonde between 01/11/1961 and 01/1964, an IPS 3D analog ionosonde with 35 mm film since 04/1964. The station was closed between 09/1974 and 08/2008. and then an IPS 5D was installed since August 2008. The IPS 5D vertical digital sounding ionosonde normally sweeps in frequency from about 1.0 to 21.5 MHz. Frequency step resolution for the 5D is 5 kHz, with up to 4095 steps available. The step interval is variable, becoming more coarse at higher frequencies as ionograms are generally displayed on a logarithmic scale.