drill circuit

drill circuit

[′dril ‚sər·kət]
(communications)
A telegraph circuit used only to practice sending and receiving.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Hot Shot; every board shop from here to Timbuktu has this in common--they drill circuit boards!