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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



necessary to wipe the excess lubricant from the surface to obtain satis- 

 factory operation. 



The lubricant in this particular recording medium was chosen for 

 operation in central offices and similar locations where temperature 

 ranges are moderate. If extreme temperatures are to be encountered the 

 lubricant problem will have to be re-examined. Continued research in this 

 field should result in improvement in this characteristic. 



In life tests, five million message repetitions have been obtained with 

 insignificant wear of the band and the magnetic head, and with no 

 measurable deterioration in the level and ciuality of the recording after 

 an initial level drop of about 2 db which occurs during the first few 

 reproductions. The head pressure is a significant factor affecting the 

 life, and in these tests a head pressure of 25 grams was used with a 

 0.100 inch wide head. 



This medium represents some compromise in the attainable trans- 

 mission properties to favor the physical properties desired for reliability 

 and long life, but the transmission is entirely adequate for the intended 

 applications. 



A typical frequency response characteristic is shown in Fig. 2. This 

 is representative of the results obtained when the equipment is main- 

 tained by field personnel. The output level, also indicated by Fig. 2, 

 is from 8 to 12 db below that obtained from commercial coated magnetic 

 tape. This is largely because the concentration of magnetic oxide, on a 

 volume basis, cannot be made as high in the impregnated material as is 

 possible in the coating of conventional tape. This is not a serious dis- 

 advantage, however, as the level is high enough to permit amplification 

 without special precautions in regard to noise. 



60 80 100 200 



FREQUENCY 



400 600 1000 2000 



vl CYCLES PER SECOND 



Fig. 2 — Frequency response of magnetic recording equipment using iron oxide 

 impregnated molded neoprene bands. 



