Radiometrix Ltd.,

NTR2 transceiver data sheet

Page 8

A. Helical antenna

B. Loop antenna

RF

C1

C2

C4

C3

RF-GND

C. Whip antenna

16.4cm

RF

0.5 mm enameled copper wire

close wound on 3.2 mm diameter former

433 MHz = 24 turns

Feed point 15% to 25% of total loop length

track width = 1mm

4 to 10 cm inside area

wire, rod, PCB-track or a combination

of these three

433 MHz = 16.4 cm total from RF pin.

2

RF

Figure 4: 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.