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Z Code (like Q Code and X Code) is a set of operating signals used in CW, TTY and RTTY radio communication. There are at three 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, one independently developed by NATO forces later for military needs and use, and one developed by APCO[1]. The NATO Z Code is still in use today, and is published in the unclassified document ACP-131. There are other sets of codes internally used by Russia's military and other operating agencies. The old C&W Z Codes are not widely used today.

Some example Z codes
Code Meaning Source
ZAL I am closing down (until...) due to.... C&W
ZAP Work...
1. Simplex;
2. Duplex;
3. Diplex;
4. Multiplex;
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
ZUJ Stand by. NATO

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.

See also[edit]


  1. ^ "Standard Z Signals". APCO International Historical Collection. 

External links[edit]


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