REFERENCE SYSTEM FOR TELEPHONE TRANSMISSION 551 



Rr = Impedance of receiver plus cord. 

 Rf = Fixed resistance. 

 Pr = Pressure developed by receiver per volt across receiver 



terminals. 

 Et = Voltage developed by condenser transmitter per bar (one 



dyne/cm^.). 

 A = Ratio of voltage delivered to 600-ohm load by the transmitter 



amplifier to voltage impressed in series with condenser 



transmitter. 

 Na = Attenuator reading with switches on "A." 

 Nb = Attenuator reading with switches on "B." 



C = Coupler (Fig. 7). 

 CT = Condenser transmitter. 



With the switches indicated in Fig. 9 in position "A" the attenuator 

 is adjusted to position Na to produce a convenient deflection on the 

 voltmeter (Ffm). Then: 



VvM = Vo-^^t^PrEtA X 10(-o-0'^^"\ 

 Rr -r Rf 



Operating the switches to position "B" and adjusting the attenuator 

 to some position Nb to reproduce the above voltmeter deflection 

 VvM we obtain : 



VvM = VoA X W-^-<^'^^\ 

 Then: 



(Rr + Rf) X loo-os^^o-^") 



Pr = 



RrEi 



The calibrations of the purely electrical elements of the circuit are 

 made by measurements of input, output, and impedance. 



Fig. 10 shows, for particular amplifier adjustments which are dis- 

 cussed below, the frequency response characteristics of the reference 

 transmitter, reference receiver and the complete reference system with 

 db in the line. The characteristic of the reference transmitter and 

 also of the reference receiver, in each instance, is that of the instru- 

 ment and associated amplifier combined. However, as the frequency 

 response of each of the amplifiers is uniform within 2 db from about 

 50 to 10,000 cycles per second, the curves shown are essentially the 

 calibrations of the instruments determined as described above. The 

 primary purpose of these characteristics is to show the performance of 

 these elements for definitely specified physical conditions. Conse- 

 quently, no corrections are included in these curves for the efi'ect on 



