. The Bell System technical journal . tual recover) time is in fact several orders of magnitudesmaller than the deionization times of the usual gas discharge so that aquite different mechanism must be involved. While an exact theory of therecovery is beyond the scope of the present paper, a qualitative picture ofthe recovery process may be of interest. During the transmitting period the free electrons provide almost all of thedischarge current, and are replenished by electron-molecule collisions. At 72 BELL SYSTEM TECHNICAL JOURNAL the end of the transmitting period these electrons may migrate
. The Bell System technical journal . tual recover) time is in fact several orders of magnitudesmaller than the deionization times of the usual gas discharge so that aquite different mechanism must be involved. While an exact theory of therecovery is beyond the scope of the present paper, a qualitative picture ofthe recovery process may be of interest. During the transmitting period the free electrons provide almost all of thedischarge current, and are replenished by electron-molecule collisions. At 72 BELL SYSTEM TECHNICAL JOURNAL the end of the transmitting period these electrons may migrate from thedischarge region, they may recombine with the positive ions, or they may becaptured by molecules to form negative ions. Negative ion formation byattachment effectively removes an electron from the discharge because ofthe great increase in mass. It is an experimental fact that those gaseswhich readily form such ions (of which water vapor is the most common)are the gases which exhibit good recovery in a TR box. This process is. TIME IN MICROSECONDS Fig. 25—A typical recovery time characteristic for the 721A tube in a TR cavity adjustedto db low level loss with a transmitter power level of 100 kw peak not deionization in the ordinar}^ sense and it can take place at a surprisinglyrapid rate. Of course, immediately upon the termination of the transmitting pulse,the cloud of free electrons will cause an extremely high loss to any reflectedsignal but the loss will rapidly decrease to some limiting value set by thefixed losses in the TR cavity itself. A typical recovery curve for the 721A tube is shown in Fig. 25. Thiscurve has a particularly fortunate shape in that the variation in loss withdistance, or more correctly with time, is at approximately the same rate asthe variation in the reflected signal level with distance for a target of fixedsize. The importance of this can be understood by considering the way in GAS-DISCHARGE TRANSMIT-RECEIVE SWITCH 73 which the reflec
Size: 1822px × 1371px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
