12 BRI.L SYSTEM TF.CIINICAL JOURXAL 



when a scjuare law detector is used and the })rograms are identical. In 

 such a case we shall assume tiiat both stations employ the same degree 

 of modulation and that therefore the q ± Ji and p ± 7i groups are of 

 the same im[)ortance. 



Interference Areas of Stations 



W'e have distinguished between three types of interference, namely, 

 carrier beat, unwanted speech and displaced side band. We shall now 

 compute, for several values of attenuation, percentage modulation 

 etc., the areas around a transmitting station inside of which each of 

 these types of interference, due to a second station, will have a relative 

 importance which is not greater than a certain specified amount. 



In estimating these areas we must deal with two possible cases which 

 may arise in practice: (1) The two stations transmit different programs. 

 (2) The programs are the same. The carriers are assumed to differ in 

 frequency in both cases. 



Case 1 



The importance of the various types of interference which are 

 present, will be determined by their ratios to the intensity of the 

 desired speech. In the present case in which the two stations transmit 

 different programs, the amount of interference which may be tolerable 

 will be determined by what occurs when the modulation of the desired 

 station is low, while that of the interfering station is high. Hence, in 

 studying this case we shall make use of Fig. 2, which gives data com- 

 puted on the basis of a modulation of 0.1 for the desired station and 

 0.5 for the interfering station. 



Taking up first the consideration of the carrier beat note, we shall 

 determine the cur\e along which the intensity of the beat is down a 

 given numl)er of db from the desired speech. The position of this 

 curve will depend on the degree of modulation of the desired signal, 

 since the lower the modulation the more noticeable \\\\\ be a beat note 

 of a given intensity. When we have specified the db difference which 

 must exist between these two components of the receiver output the 

 carrier ratio can be picked off' from the n line of Fig. 2. 



In order to determine the curve along which this carrier ratio exists 

 we shall proceed as follows: 



The desired station will be considered to be at the origin of a system 

 of rectangular coordinates and the undesired station will be at the 

 point {D, O). We shall assume that the powers of the desired and 

 undesired stations are Pi and P-i, respectively, and that their distances 

 from a point in the coordinate plane are di and J2; then if we denote the 



