Calibration of 9-ft Rod Antenna for MF and HF EMC Measurements

The 9 f t rod antenna p r o v id e s a lower r e c e iv in g system th r e sh o ld than a 4 1 in rod, and th e r e f o r e i t i s a d e s i r a b l e c h o ic e f o r v a r io u s e le c tr o m a g n e t ic com­ p a t i b i l i t y (EMC) measurements such a s environm ental n o i s e l e v e l su r v e y s . The antenna f a c t o r provided by th e m anufacturer i s f r e q u e n t ly th e i n s e r t i o n l o s s o f the antenna c o u p le r measured w ith a dummy antenna in th e la b o r a to ry r a th e r than the antenna f a c t o r as de­ f in e d by the IEEE (which in c lu d e s th e antenna e f ­ f e c t i v e l e n g t h ) . The a c t u a l antenna f a c t o r f o r any g iv e n measurement depends upon th e antenna i n s t a l l a ­ t i o n . The 9 f t rod antennas have been used w h ile mounted on aluminum ground p la n es p la ced on th e e a rth and, more r e c e n t ly , w h i le i n s t a l l e d on the to p s o f m e ta l-r o o fe d v e h i c l e s . T h is paper summarizes some measured antenna f a c t o r s fo r the 9 f t rod fo r v e r t i ­ c a l l y p o la r iz e d ground waves fo r both o f th e se con­ f i g u r a t io n s ; and com parisons w ith the m anu factu rer's v a lu e s a re g iv e n . Example inp ut impedance da ta are a l s o g iv e n f o r each type o f i n s t a l l a t i o n . F in a l l y , some comments a re o f f e r e d on th e e le v a t io n p la n e d i r e c t i v i t y p a t te r n s o f veh ic le -m o u n ted 9 f t r o d s , on th e e f f e c t s o f d i f f e r e n t ty p es o f ground, and on th e e f f e c t s o f p eo p le s ta n d in g near th e antenna.