Functional overview
The transmit section of the BiM2/3G consists of a frequency modulated crystal locked PLL feeding a buffer
amplifier and RF filter. A Tx select line controls operation. The transmitter achieves full RF output typically
within 1ms of this line being pulled low. Modulation is applied at the TXD input and may be either a serial digital
stream toggling between 0V and 5V (digital drive) or a high level analogue waveform with the same peak limits
(linear drive). Modulation shaping is performed internally by a 2nd order lowpass filter, which minimises spectral
spreading. The RF output is filtered to ensure compliance with the appropriate regulations and fed via a Tx/Rx
changeover switch to the antenna pin.
The receive section is a single conversion FM superhet with an IF of 10.7MHz. A SAW bandpass filter in the
receiver front-end provides image rejection and suppression of other unwanted out-of-band signals. Like the
transmitter, the receiver is controlled by its own active low RX select line. A post-detection lowpass filter
establishes the signal bandwidth and ensures clean operation of the subsequent adaptive data slicer. The slicer
is optimised for balanced data such as bi-phase code. A received signal strength (RSSI) output with 60dB of
range is provided. A version of BiM2/3G featuring a fast acting Carrier Detect (CD) output on the same RSSI
pin is also available. The CD output will indicate the presence of any RF signals on the carrier frequency.
side view (through can)
5 mm
side view (with can)
top view (without can)
RF GND 1
Antenna 2
RF GND 3
4
5
No pin
6
7
8
0V 9
30.48 mm
33 mm
18 0V
17 Vcc
16 RX SELECT
15 TX SELECT
14 TXD
13 AF
12 RXD
11 RSSI/CD
10 0V
23 mm
recommended PCB hole size: 1.2 mm
module footprint size: 25 x 32 mm
pin pitch: 2.54 mm (0.1")
pins 4, 5, 6, 7 & 8 are not fitted
Fig. 2: Physical dimensions
Pin description
RF GND
pins 1 & 3
RF ground pins, internally connected to the module screen and to pins 9, 10 & 18 (0V). These pins should be
connected directly to the RF return path (e.g. coax braid, main PCB ground plane etc).
Antenna
pin 2
50Ω RF connection to the antenna, DC-isolated. See pages 7 & 8 for details of suitable antennas and feeds.
0V (GND)
pins 9, 10 & 18
Supply ground connection and screen.
RSSI /CD
pin 11
RSSI variant:
Received Signal Strength Indicator with 60dB range, operational when Rx is enabled. Output
voltage nominally 0.50Vdc (no signal), 1.0Vdc (maximum strength). See page.6 for typical characteristics.
Carrier Detect variant:
When the receiver is enabled, a low indicates a signal above the detection threshold is
being received. The output is high impedance and should only be used to drive a CMOS logic input.
Radiometrix Ltd, BIM2/3G Data Sheet
page 2
RADIOMETRIX [ RADIOMETRIX LTD ]
