BF.IJ. SYSTEM TliCIIXIC.U. JOVRXAL 



In general the method cm|)lo\f(l in nif.isuriiig the signal t'leUl 

 strength is a compiarison one. A reference radio-frequency \ollage 

 of known \alue is introduced in the loop antenna and adjusted to 

 give the same receiver output as that from the distant signal. This 

 is determined either by aural or visual means. Under such condi- 

 tions equal voltages are introduced in the antenna from local and 

 distant sources, and by calculating the effective height of the loop 

 I he (ield strength of the received signal is determined. 



Ill the noise measurements, static noise is admiited ihr(iiii;h a 

 delinite frequency band appro.ximately 2,700 cycles wide. -A ioral 

 ra(lio-frec]uency signal of known and adjustable voltage is tlun in- 



5iGN»L TiELD rooM Rockv PointLI. 2XS 

 Received at New Southgate Cng ScptK-15 I92 < 

 °b«D .R»«fe20|Kw| STtoOOhvcik r 



Kig. 5 — Diurnal variation in signal field 



lrii<iuci-(l. riic ra(lio-frc(|iii'nc\' sounx' of this siijnal is subji'cti'd to a 

 continual frec|iienc\- fluctuation so that the detected note has a 

 warliling sound. This is done in order that the effect of static upon 

 speech can be more closely simulated than by using a steady tone. 

 The intensity of the signal is then adjusted to such a value tliat 

 further decrease results in a rapid extinction. The comparison 

 signal is then ex[)ressed in terms of an e(iui\alent radio field strength. 

 Thus the static noise is measured in terms of a definite reference 

 signal with which it interferes and is expressed in microvolts per 

 meter. 



