Antenna requirements
Three types of integral antenna are recommended and approved for use with the module:
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.8: Antenna
A
helical
**
**
***
**
B
loop
C
whip
***
***
*
Ultimate performance
Easy of design set-up
Size
*
*
**
***
Immunity proximity effects
*
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
C) Whip
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.
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
The antenna choice and position directly controls the system range. Keep it clear of other metal in the
system, particularly the 'hot' end. The best position by far, is sticking out the top of the product. This is
often not desirable for practical/ergonomic reasons thus a compromise may need to be reached. If an
internal antenna must be used try to keep it away from other metal components, particularly large ones
like transformers, batteries and PCB tracks/earth plane. The space around the antenna is as important
as the antenna itself.
sales@radiometrix.com
TX2H – Data
Page - 4 -
RADIOMETRIX [ RADIOMETRIX LTD ]
