Radiometrix Ltd, BiM2 Data Sheet
page 6
Baseband Transfer
Performance
pin
min.
typ.
max.
units
notes
Signal applied with supply on
Signal to valid CD,
tsig-CD
11
-
0.25
0.5
ms
Note 2
Signal to stable data, tsig-data
12
-
3
4
ms
Signal to stable data, tsig-data
12
-
-
1
ms
1, S version
Signal to stable data, tsig-data
12
-
-
0.5
ms
TX power up to full RF
2
-
100
-
µs
Notes:
1. from 45% to 55% duty cycle
2. CD works up to a temperature of 40° C
Antenna requirements
Three types of integral antenna are recommended and approved for use with the module:
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 16cm (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
B
C
helical
loop
whip
Ultimate performance
**
*
***
Easy of design set-up
**
*
***
Size
***
**
*
Immunity proximity effects
**
***
*
Range open ground to similar antenna
200m
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.