0.5 mm enameled copper wire
close wound on 3.2 mm diameter former
RF
433 MHz = 24 turns
A. Helical antenna
Feed point 15% to 25% of total loop length
RF-GND
C2
C3
C4
C1
track width = 1mm
4 to 10 cm inside area
2
RF
B. Loop antenna
16.4cm
wire, rod, PCB-track or a combination
of these three
RF
C. Whip antenna
433 MHz = 16.4 cm total from RF pin.
Figure 5: integral antenna configurations
External antennas
These have several advantages if portability is not an issue, and are essential for long range links. External
antennas can be optimised for individual circumstances and may be mounted in relatively good RF locations
away from sources of interference, being connected to the equipment by coax feeder.
Helical.
Of similar dimensions and performance to the integral type mentioned above, commercially-
available helical antennas normally have the coil element protected by a plastic moulding or sleeve and
incorporate a coax connector at one end (usually a straight or right-angle BNC/SMA type). These are
compact and simple to use as they come pre-tuned for a given application, but are relatively inefficient and
are best suited to shorter ranges.
Quarter-wave whip.
Again similar to the integral type, the element usually consists of a stainless steel rod
or a wire contained within a semi-flexible moulded plastic jacket. Various mounting options are available,
from a simple BNC/SMA connector to wall brackets, through-panel fixings and magnetic mounts for
temporary attachment to steel surfaces.
A significant improvement in performance is obtainable if the whip is used in conjunction with a metal ground
plane. For best results this should extend all round the base of the whip out to a radius of the length of the
whip used (under these conditions performance approaches that of a half-wave dipole) but even relatively
small metal areas will produce a worthwhile improvement over the whip alone. The ground plane should be
electrically connected to the coax outer at the base of the whip. Magnetic mounts are slightly different in that
they rely on capacitance between the mount and the metal surface to achieve the same result.
A ground plane can also be simulated by using 3 or 4 quarter-wave radials equally spaced around the base
of the whip, connected at their inner ends to the outer of the coax feed. A better match to a 50Ω coax feed
can be achieved if the elements are angled downwards at approximately 30-40° to the horizontal.
Radiometrix Ltd.,
WRX2 data sheet
Page 6
RADIOMETRIX [ RADIOMETRIX LTD ]
