An improved formula is derived for accurately computing the near-zone magnetic field of a s mall c irc ular transmitting loop an tenna. Such a field can serve as a reference standard for calibrating fi eld-strength meters e mploying small receiving loop anten nas in the fre qu ency range 30 Hz to 30 MHz.This formula in c ludes correction terms for fr equ ency (d ue to the finite tim e of propagation), as well as correction s for the finite radii of both the transmitting and rece iving loop s. Other formula s appearing in the literature often fail to include s uch correc tion s whic h can result in errors of up to 20 pe rcent a nd more in co mputin g standard-fie ld valu es.The N BS formula is de riv ed by ex pandin g th e integran d of the re tard ed vector potentia l into an infinite se ri es of sp he ri ca l Ha nk e l fun c ti ons of in creasing o rde r. Th e res ulting series express ion is in e rror by less than 0.2 pe rce nt , is rap idl y co nverging and si mpl e to use without reco urse to a tabl e of fun c tio ns or a co mpute r.Key Woro s : l."" p-a nl e nn a field s lrc n~I". Illa~neli(" fie ld -s lre n~lh s la nd ard . Illulual indu c la nce IIf ('oaxi a l c ircular filam e nt s . Ilear·zone magne ti c fi e ld , tran s mitting loop antenna.
A descriptio0 is given of the CW t"ms@h stamla& and essociptedmepsrwment' ' tationdteceairleeqdforthecnlibmt i o a o f b o t h c o m m e r c i n l d m i l i t u y f i e l d-s t r e o g t h~m v~f r eq w o c y~o f t h e o v~r r n g e~3 0 H z t o l O O O M H z , r r h i e h b s v e~ developedattheNa~WlreraofSt.nQrdsdPriagthepPst25to30yePrs '2be techaiqws are rppliaMe only for evaluating the streegth ofsteady4ate, a c f i e l d s v a r y h g~m t i m e , a n d a r e. o t~f o r p s e~l w o a dband appiicatbm of any kind. Twopri&paltypesofWdrengthstmdar&dapdotypenear-zone 6eId-&engtb meter are described: 1) umgne&&M4rm@b s t d a d s (30 Hz to 30 MHz), 2) e l &-6 e h l e e m g t h st.adnrdf (3 0 to lo00 MHz), and 3) near-zooe electric-fidd-strength meter a d interim kkl-streogth stamhrds (150 kHz to 30 MHz).
A description is given of t he development of two very-high-frequency field-intensity standards, which are being used at this Bureau for t he calibration of commercial fieldintensity sets in the range 30 t o 300 megacycles. These standards are employed to establish known values of field intensity by eit her of two methods : (a) the standard-antenna method in which t he open-circuit voltage at the center of a receiving dipole is measured directly ; (b) t he standa rd-field met hod in which the current at the center of a t rans mitting dipole i acc urately known. The techniques u ed for determini ng t he antenna current and voltage are described.The current di stribution on the antenna is determined th eoretically, using Schelkunoff's method, which gives the effective length. These values are compared with t hose obtained by measurement.R es ults of field tests at 100 megacycles are presented in which t he above two m ethods were directly intercompared using horizontal polarization. Their accuracy and limitations aTe discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.