Z Code (like Q Code and X Code) is a set of operating signals used in CW, TTY and RTTY radio communication. Actually, there are different sets of Z-codes: one originally developed by Cable & Wireless Ltd. (the Cable & Wireless Service Z-Code), for commercial communications in the early days of wire and radio communications, another one independently developed by NATO forces later for military needs and use. The NATO Z Code is still in use today, and is published in the unclassified document ACP-131. There are other set of codes internally used by Russia's military and other operating agencies. The old C&W Z Codes are not widely used today.
|ZAL||I am closing down (until...) due to....||C&W|
5. Single Sideband;
6. With automatic error correction system;
7. Without automatic error correction system.
8. With time and frequency diversity modem
|ZBK||Are you receiving my traffic clear?||NATO|
|ZBK1||I am receiving your traffic clear||NATO|
|ZBK2||I am receiving your traffic garbled||NATO|
|ZBM2||Place a competent operator on this circuit||C&W|
|ZLD2||I cannot transmit pictures.||C&W|
|ZSF||Switch off...(1. IFF; 2. IFF sets for 10 minutes in area denoted except for ships whose call signs follow).||C&W|
|ZBW no.||Change to backup frequency no.||C&W|
|ZBZ(1-5).||Measure of Printability (Where 1=Garbled/unreadable & 5=Perfect)||C&W|
A lot of the old C&W codes are derived from mnemonics (ZAL = (a)lter wave(l)ength, ZAP = (a)ck (p)lease, ZSF = (s)end (f)aster, etc.