Radiometrix Ltd, BIM2/3G Data Sheet

page 8

Three types of integral antenna are recommended:

A) Helical

Wire coil, connected directly to pin 2, open circuit at other end. This

antenna

is

very

efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim the wire

length or expand the coil for optimum results. The helical de-tunes badly with proximity to other

conductive objects.

B) Loop

A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed

from pin 2 at a point 20% from the ground end. Loops have high immunity to proximity de-

tuning.

C) Whip

This is a wire, rod, PCB track or combination connected directly to pin 2 of the module.

Optimum total length is 15.5cm (1/4 wave @ 433MHz). Keep the open circuit (hot) end well

away from metal components to prevent serious de-tuning. Whips are ground plane sensitive

and will benefit from internal 1/4 wave earthed radial(s) if the product is small and plastic cased

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

helical

loop

whip

Ultimate performance

**

*

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Easy of design set-up

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*

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Size

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Immunity proximity effects

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*

Range open ground to similar antenna

(for BiM2G-433-15)

200m

100m

300m

Fig.4: Antenna configuration (BiM2G @ 433.92MHz)

Antenna selection chart