MULTICHANNEL AMPLIFIERS BELOW OVERLOAD 



595 



retically it should be possible to compute the S.T.M.F. for any par- 

 ticular product if sufficient information concerning the properties of 

 speech, the transmitting and receiving instruments, the carrier system 



2 3 4 



CARRIERS 



Fig. 1 — Spectra of second order modulation products 

 from two fundamental channels. 



itself, and the ear were known, but in practice it is found best to use 

 experimental determinations. In the case of new systems for which 

 experimental data are not available, estimates based on known systems 

 of similar type would be used. 



6. Number of Products Falling in Individual Channels 



In the appendix it is explained how the total number of possible 

 products of each type falling in individual channels may be counted. 

 Table II shows the result of counting all second and third order type 

 products.^ Results for products falling both within and without the 

 fundamental band are given. In certain of the {A -\- B — C)- and 

 {A — B — C)-type products, the channel in which the product occurs 

 also is the source of one of the fundamentals. Since this would give a 

 type of interference heard only when the disturbed channel is also 

 carrying signal, it is not in general as serious a form of crosstalk as the 

 cases of independent fundamental and product frequencies. Therefore 

 the number of these special kinds of products has also been evaluated 



* Mr. J. G. Kreer collaborated in the derivation of these formulae. 



