. Practical wireless telegraphy; a complete text book for students of radio communication . smittingstations is often desirable for purposes of record or adjustment, more accuratemeans must be provided. The ideal way to measure the strength of the incoming signals would be to place agalvanometer in the receiver circuits, but this is not feasible, particularly whenthe receiving station is far distant from the transmitter or in case discharges ofatmospheric electricity are rather severe. Hence the measurement is carried out by meansof a calibrated shunt resistance connected across the receiving
. Practical wireless telegraphy; a complete text book for students of radio communication . smittingstations is often desirable for purposes of record or adjustment, more accuratemeans must be provided. The ideal way to measure the strength of the incoming signals would be to place agalvanometer in the receiver circuits, but this is not feasible, particularly whenthe receiving station is far distant from the transmitter or in case discharges ofatmospheric electricity are rather severe. Hence the measurement is carried out by meansof a calibrated shunt resistance connected across the receiving telephone. The measurement of the signal intensity is carried out as follows: A given transmitteris tuned to maximum strength of signals at the receiver, followed by connecting a variableresistance across the telephones, the resistance being reduced until the signals just disappearor are barely audible. If we designate the value of the telephone current in microamperes required to makethe least audible signal as C-a, it has been shown that PRACTICAL RADIO MEASUREMENTS. 217 R + T R X C-a. where C := current in the telephone without the shunt; R ^= resistance of the shunt for the least audible signal;T = resistance of tlic telephone. Now the value of C-a for the least audiblesignal varies with the frequency of thecurrent flowing through the telephone, theimpedance of its windings, and the sensi-tiveness of the human ear to weak at a given station the value of C-ais ignored and the strength of the signalspoken of as being so many times audi-bility. Thus as in the diagram, Fig. 237, ifthe value of R for the least audible signalis 50 ohms, and the resistance of the tele-phone 2,000 ohms, then2,000 -I- SO C = C-a = 41, C-a, e. g., 50the signal is 41 times that required to makean audible sound in the is clear that the results obtained by this method vary at each station according to thetype of apparatus and the keenness of the observer, hence the audibility f
Size: 2367px × 1056px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
