. The Bell System technical journal . hermal ammeter in the antenna circuit is also carried back to abracket-mounted instrument on the end of the transmitter. Thesefacilities permit the antenna tuning to be checked and adjustments RADIO BROADCASTING TRANSMITTERS 133 made to compensate for minor variations in antenna conditions with-out leaving the operating room. Another feature of interest is the artificial antenna shown in Fig. unit is essentially a 600-ohm non-inductive resistance capable ofdissipating approximately 75 kw. which can be connected to theoutput circuit of the final powe
. The Bell System technical journal . hermal ammeter in the antenna circuit is also carried back to abracket-mounted instrument on the end of the transmitter. Thesefacilities permit the antenna tuning to be checked and adjustments RADIO BROADCASTING TRANSMITTERS 133 made to compensate for minor variations in antenna conditions with-out leaving the operating room. Another feature of interest is the artificial antenna shown in Fig. unit is essentially a 600-ohm non-inductive resistance capable ofdissipating approximately 75 kw. which can be connected to theoutput circuit of the final power amplifier stage in place of the trans-mission line. The heat dissipating elements consist of a series ofwoven wire grids mounted in the units at the top of the resistance of these grids is substantially independent of frequency,but the combination presents a slight inductive reactance which iscompensated for by means of the condenser and coil combinationshown. These elements are inserted into the circuit symmetrically. Fig. 8—Piezo-electric crystal mounting and temperature control apparatus. in order to maintain an approximate balance to ground. The struc-ture is completely shielded and is fitted with safety door and ground-ing switches similar to those already described. The piezo-electric crystal mounting and temperature-control appa-ratus which is a part of the oscillator-modulator unit is shown inFig. 8, dismantled to facilitate inspection. The quartz plates em-ployed are approximately one and a quarter inches square and arecut parallel to one of the faces of the natural rock crystal. This plateis mounted between two lapped metal plates and covered with aporcelain cap carrying a terminal to which the upper electrode isconnected by means of a short section of metal foil. The mountedcrystal is supported by a brass block, through the center of whichextends a spiral bimetallic thermostat. The top of the block is alsolapped and the crystal mounting is secured t
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
