. The Bell System technical journal . a resonant cavity to a transmission line by awindow is not limited to the coaxial line case. A wave guide system is shownin Fig. 11. The distance between the TR cavity and the transmitting tubeis again adjusted by sliding the cavity and its window along over a sectionof the rectangular wave guide containing a slot. The ATR. In all of the systems so far described use is made of theimpedance mismatch conditions at the magnetron or other transmittingtube terminals to prevent serious loss during the receiving period. If the GAS-DISCHARGE TRANSMIT-RECEIVE SWITC
. The Bell System technical journal . a resonant cavity to a transmission line by awindow is not limited to the coaxial line case. A wave guide system is shownin Fig. 11. The distance between the TR cavity and the transmitting tubeis again adjusted by sliding the cavity and its window along over a sectionof the rectangular wave guide containing a slot. The ATR. In all of the systems so far described use is made of theimpedance mismatch conditions at the magnetron or other transmittingtube terminals to prevent serious loss during the receiving period. If the GAS-DISCHARGE TRANSMIT-RECEIVE SWITCH 57 magnetron cold impedance docs not differ greatly from the surge imped-ance of the transmission line used, it may not be possible to avoid loss ofreflected signal into the transmitter line. Also in some cases, an unreason-able amount of adjustment must be provided in the position of the TRcavity with respect to the transmitter to make up for large variations whichmay be encountered in transmitter cold impedance. Both difficulties. Fig. 8—Series branching circuit using the 1H2S vacuum tube may be avoided by the use of a second gas discharge tube located betweenthe transmitter and the TR and at an odd number of quarter wavelengthsfrom the TR junction. This second tube is referred to as the anti-T-R tube(usually abbreviated to ATR), or sometimes as the RT tube. The use ofan ATR tube was not found to be necessary in most of the systems whichemployed the 721A tube. With the advent of still higher frequency systems, for which the 724Btube was designed, the cold impedance difficulties just mentioned made
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