Base-loaded whip. In applications where space is at a premium a shortened whip may be used, tuned
by means of a coil inserted at the base. This coil may be air-wound for maximum efficiency, or a small
SMT inductor can be used. The value must be empirically chosen to tune the particular length of whip
for best results “in situ”, making this antenna more difficult to set up. Radiated power will generally be
slightly less than that obtained from a ¼-wave whip.
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
track width = 1mm
RF-GND
4 to 10 cm2 inside area
C2
C1
RF
C3
C4
B. Loop antenna
16.4cm
wire, rod, PCB-track or a combination
of these three
RF
433 MHz = 16.4 cm total from RF pin.
C. Whip antenna
Fig. 5: Antenna configurations
Note: Where the specified antennas are mounted on the PCB and/or in close proximity to metalwork
(module casing, components, PCB tracking etc), the antenna radiation pattern may be seriously affected.
Radiated power may be significantly increased in some directions (sometimes by as much as 10dB) and
correspondingly reduced in others. This may adversely affect system performance where good all-round
coverage is desired.
Care should also be taken to ensure that this effect does not increase the radiated power in any direction
beyond that allowed by type approval regulations. Where this occurs the antenna may need to be
relocated. In extreme cases a resistive attenuator of appropriate value may be required between the
module and antenna.
Type Approval requirements: Europe
The modules comply with the requirements of the R&TTE Directive (including standards EN 300 220-3
and EN 301 489-3) when used in accordance with the information contained herein. The following
provisos apply:
1) The modules must not be modified or used outside their specification limits.
2) The modules may only be used to transfer digital or digitised data. Analogue speech and/or
music are not permitted.
3) The equipment in which the BiM2A is used must carry all necessary external labelling to meet
the requirements of the R&TTE directive.
4) The BiM2A has not been tested with antennas having gains greater than that of a quarter-wave
whip. The use of such antennas may require further R&TTE approval.
Radiometrix Ltd, BiM2A Data Sheet
page 7
RADIOMETRIX [ RADIOMETRIX LTD ]
