Radiometrix Ltd.,
BiM1 transceiver, TX1H high power transmitter data sheet
Page 6
Applications information
Power supply requirements
The BiM1 have built-in regulators which deliver a constant 3.5V to the transmitter (100mW) and 2.8V
to the receiver circuitry when the external supply voltage is 3.8V or greater. This ensures constant
performance up to the maximum permitted rail, and removes the need for external supply decoupling
except in cases where the supply rail is extremely poor (ripple/noise content >0.1Vp-p).
TX modulation requirements
The module is factory-set to produce the specified FM deviation with a TXD input to pin 14 of 3V
amplitude, i.e. 0V “low”, 3V “high
If the data input level is greater than 3V, a resistor must be added in series with the TXD input to limit
the modulating input voltage to a maximum of 3V on pin 7. TXD input resistance is 100k
Ω to ground,
giving typical required resistor values as follows:
Vcc
Series resistor
≤3V
3.3V
5V
9V
-
10 k
Ω
68k
Ω
220k
Ω
Reducing the output power of the BiM1
If the BiM1 is to be used for applications for which the regulatory Effective Radiated Power (ERP) limit
is lower than 100mW its output power can be reduced to comply with relevant regulatory requirements.
This is done by inserting a 10dB attenuator network between the module and the antenna or feed, as
follows:
1
2
3
9
18
10
68R
100R
To antenna
68R
ground foil/
vias to ground plane
50 ohm microstrip lines
to antenna
from TX1
schematic diagram
physical arrangement
Resistors are SMD (0603/0805)
Antenna
RF Ground
RF Ground
Figure 6: 10dB attenuator for BiM1 transceiver, BiM1T transmitter
Keep all tracking around the attenuator network as short as possible, particularly ground paths, and
use matched 50
Ω microstrip lines for input and output connections (track width of 2.5mm if using
1.6mm thick FR4 PCB).
However, this 10dB attenuator will also reduce the sensitivity of the BiM1 transceiver by 10dB.
RF output can also be factory set from +5dBm (3mW) to +20dBm (100mW) depending on minimum
order quantity.
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