RECORDING TRANSMISSION MEASURING SYSTEM 



29 



is received. Knowing the time frequency characteristics of the oscil- 

 lator the entire frequency range can then be added by means of a 

 rubber stamp. When time markings are desired the marking device 

 may be operated by an external time clock. There is, of course, 

 nothing in the design of the meter which would prevent using ruled 

 paper in case this should be desirable. 



The oscillator of the recording system is of the heterodyne type 

 which uses a single dial for frequency adjustment, the frequency being 

 varied continuously from one end of the range to the other as the dial 

 is turned. When transmission-frequency curves are made a motor is 

 connected to the dial , turning it at a uniform rate. The time-frequency 

 scale of the oscillator is neither uniform nor logarithmic, as will be 



60 SECONDS 



Fig. 6 — Transmission frequency characteristic of message telephone 

 circuit A. 



noted in Figs. 6 to 8, being a compromise which gives sufficient space 

 on the record to all parts of the range which are of particular interest. 



A number of typical curves made by the recording system are shown 

 in Figs. 6 to 12. Figures 6 and 7 are transmission-frequency character- 

 istics of two telephone message circuits, each curve having been made 

 in about one minute, using a paper speed of 10 inches per minute. 

 Fig. 8, which is a transmission-frequency curve for a wide-band pro- 

 gram circuit, was made in 30 seconds. Although a wide frequency 

 range is covered by this curve, the absence of rapid transmission vari- 

 ations in the program circuit permitted a rapid change of the oscillator 

 frequency. 



Figures 9 and 10 were made with the slow rate of paper feed and 

 are records of 24-hour continuous measurements on message telephone 



