Radiometrix Ltd.,

NTX2/NRX2 data sheet

Page 9

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 7: 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 50

Ω

coax feed can be achieved if the elements are angled downwards at approximately 30-40

° to the

horizontal.