In its most basic form, 2-channel (L, R) UHJ, horizontal (or "planar") surround information can be carried by normal stereo signal channels – CD, FM or digital radio, etc. – which may be recovered by using a UHJ decoder at the listening end. Summing the two channels gives a highly compatible mono signal which in fact is a more accurate representation of the two-channel version than summing a conventional "panpotted mono" source. If a third channel (T) is available, this can be used to give improved localisation accuracy to the planar surround effect when decoded via a 3-channel UHJ decoder. The third channel does not have to have full audio bandwidth for this purpose, leading to the possibility of so-called "2½-channel" systems, where the third channel is bandwidth-limited to 5 kHz. The third channel can be broadcast via FM radio, for example, by means of phase-quadrature modulation. This configuration was tested by the Independent Broadcasting Authority (IBA) in the United Kingdom as a method of broadcasting surround recordings. 2½ or 3-channel UHJ delivers the same accuracy as 3-channel (WXY) B-Format. Adding a fourth channel (Q) to the UHJ system allows the encoding of full surround sound with height, known as Periphony, with a level of accuracy identical to 4-channel B-Format.