COMMON FREQUENCY BROADCASTING 589 



variations in plate voltage at WHO, which were permitted in the in- 

 terest of economy, since the ensuing variations of the two carriers were 

 still far within the requirements of the Federal Radio Commission. 



More recent measurements made on a similar unit installed in a 

 broadcast station where precautions have been taken to insure the 

 application of a constant plate voltage to the oscillator have shown a 

 frequency variation of less than five cycles per second from the as- 

 signed value over a period of several weeks. 



Before approval was sought from the Federal Radio Commission 

 for the full time simultaneous operation of these stations on a common 

 frequency, careful surveys of the areas served were made by the engi- 

 neers of the Federal Radio Commission, the Department of Commerce, 

 the Central Broadcasting Company, and Bell Telephone Laboratories 

 during their simultaneous operation on an experimental basis during 

 the early morning hours in order to determine the nature of the service 

 being rendered. Nearly three thousand miles were covered by the 

 radio test cars during these tests. Upon completion of these surveys 

 the Federal Radio Commission immediately granted permission for the 

 simultaneous operation of WHO and W^OC during regular broadcast 

 hours. 



These surveys showed that the service rendered by the simultane- 

 ous operation of these two stations was substantially twice as great as 

 the service given on a shared time basis. The normal service area of 

 each station was maintained and the nighttime reception at points over 

 a hundred miles distant from either station was improved by the par- 

 tial elimination of rapid and selective fading as well as by an increase 

 in the average field strength received. 



This improvement in distant reception was confirmed by the letters 

 received in response to requests, made during the tests, for reports as 

 to the quality of reception. In making these requests, the nature of the 

 distortion that might be experienced was carefully described and it was 

 especially emphasized that mere reports of reception would be of no 

 value and that the information desired concerned the quality of the 

 program received during the simultaneous operation of the stations as 

 compared to that from either one alone. Several hundred replies were 

 received from outside the State of Iowa beyond the normal service 

 range of either station. These were almost unanimous in reporting 

 better reception with simultaneous operation. The reports received 

 from distant points during the first year's commercial operation are in 

 full accord with these test data. This improvement apparently occurs 

 wherever marked selective and general fading is experienced in the 

 reception of either station alone. 



