Practical_Antenna_Handbook_0071639586

C h a p t e r 2 7 : T e s t i n g a n d T r o u b l e s h o o t i n g 599
Figure 27.7 Dip meter.
Radiator
Base
insulator
Dip meter
circuit resonant frequency. This energy loss shows up on the meter pointer as a slight
“dipping” action. The dip is extremely sharp and is easily missed if the meter frequency
dial is tuned too rapidly.
When using a dip meter to check lumped-Âcomponent tank circuits, maximum coupling
is usually obtained by orienting the coil of the meter the same as the coil of the
circuit. Figure 27.8A shows one way to couple the dip oscillator to a vertical antenna
radiator. The coil of the dipper is brought into close proximity to the base of the radiator.
Figure 27.8B shows the means for coupling the dip oscillator to systems where the
antenna is not easily accessed directly
(as when the antenna is at the top of a
mast). A small two-Â or three-Âturn loop
can be connected across the transmitter
end of the transmission line, and
the coil of the dipper brought close
to it.
Dip meters absolutely shine at
checking individual traps from multiband
Yagi antennas or trap dipoles.
A search of the antenna manufacturer’s
Web site is likely to unearth a service
bulletin describing the procedure
to be followed for each company’s
products. The service bulletin dip
meter procedure is especially helpful
with traps for certain Cushcraft an-
Mount
Figure 27.8A Direct coupling the dip
meter to antenna.