A Static Recorder 



By H. T. FRIIS 



Synopsis: This paper discusses different tyi)es of apparatus for record- 

 ing static and also describes a new instrument in which the output of the set 

 is kept constant by automatic control of the ampHfication, this ampHfication 

 then being recorded as the relative measure of static. The set makes use of 

 a fluxmeter with zero restoring torque by means of which the rectified 

 output current arising from static interference is integrated over a period 

 of ten seconds. The following five seconds are required to adjust the gain of 

 the amplifier and record the change in gain from an arbitrary level. 

 The gain is recorded in stops of 4 TU which correspond to a power amplifi- 

 cation change by approximately a factor of 2.5. A record is shown during 

 which the intensity of static changed by a factor of more than 10,000. 



IN the following is given a general discussion of receiving sets for 

 recording static and also a detailed description of a new instru- 

 ment of this kind which is based upon the principle that the output of 

 the set is kept constant by automatic control of the amplification, this 

 amplification then being recorded as the relative measure of the static. 



The literature on manual measurements of static is plentiful and for 

 e.xtensive references the reader may be referred to a paper on "Present 

 Status of Atmospheric Disturbances," presented by L. W. Austin 

 before the American Geophysical Union.' Many different methods 

 of measuring static have been employed in obtaining the results given 

 in this paper and it may further be added that we have found that the 

 most reliable method of measuring the effect of static upon the intel- 

 ligibility of speech signals is to introduce a local warbler signal ^ in 

 the antenna. Unfortunately, however, all manual measurements 

 require trained observers and therefore the cost of making continuous 

 measurements will always be high, and besides, the human element 

 introduced will decrease their reliability. 



Very little has been published on automatic recording of static. 

 The American Telephone and Telegraph Company and the Western 

 Electric Company in 1923 developed an automatic static recorder 

 which measured the high frequency currents induced in a loop antenna 

 by amplifying them and passing them through a recording thermo- 

 couple meter. This apparatus was also equipped with a means of 

 automatically measuring the gain of the entire receiving device so 

 that the energy of the static could be evaluated directly. A popular 

 account of this device was given under the caption "Getting Static's 

 Autograph" by Austin Bailey in "Popular Radio," May, 1924. A 

 recorder working at Aldershot, England, is mentioned in a paper by 



1 Will be published in the Proc. I. R. E. probably in the February, 1926, number. 

 *See "Radio Transmission Measurements," by Bown, Englund and Friis, Proc. 

 I. R. E. Vol. 11, No. 2. 



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