BIM2A

433MHz Wide Band FM radio transceiver

BiM2A is half-duplex crystals controlled PLL wideband FM transceiver operating on 433.05-434.79MHz European SRD band.

It is an enhanced replacement for the SAW based BiM2 and has better frequency accuracy and temperature stability.
The module is ideal for enabling bi-directional wireless connectivity in battery powered or hand held applications.

 

Figure 1: BiM2A-434-64

Features

  • Complies with European harmonised standards EN 300 220-3 and EN 301 489-3
  • Data rates up to 64kbps
  • Crystal controlled PLL FM circuitry for both Tx and Rx
  • Receiver Sensitivity:  -101dBm for 1ppm BER (64kbps)
    -104dBm for 1ppm BER (10kbps)
  • Supply: 2.9V - 16V @ 13mA TX (10mW), 11mA Rx
  • Usable range up to 300 metres external, 75 metres in building
  • SAW front end filter and full screening
  • RSSI (standard) or carrier detect option
  • Analogue and digital baseband
  • Low profile with small footprint
  • 33 x 23 x 5mm

Applications

  • PDAs, organisers and laptops
  • Wireless handheld terminals
  • EPOS equipment, barcode scanners, belt clip printers
  • Data loggers
  • Audience response systems
  • In-building environmental monitoring and control
  • Security and fire alarms
  • Restaurant ordering systems
  • Vehicle data up/download

Evaluation Platform: Universal Evaluation kit or Narrow Band Evaluation Kit

Functional description

The transmit section of the BiM2A/H 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 3V (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. The standard module features a received signal strength (RSSI) output with 60dB of range. A version of BiM2A 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.


Figure 2: Block diagram

User Interface


Figure 3: BiM2A pin-out and dimension

Pin description:

RF GND     pin 1 & 3
RF ground pin, internally connected to the module screen and pin 5, 9, 10, 18 (0 Volt). This pin should be connected to the RF return path (e.g. coax braid, main PCB ground plane etc.)

Antenna   pin 2
50W RF input from the antenna, it is DC isolated internally. (see antenna for suggested antenna/feeds).

0Volt        pins 5, 9, 10 & 18
Supply ground connection and screen.

RSSI         pin 11
Received Signal Strength Indicator with 60dB range, operational when Rx is enabled. Output voltage nominally 0.17-0.33Vdc (no signal), 1.25Vdc (maximum). See page.6 for typical characteristics.

CD (CD version)    pin 11
Carrier Detect - When the receiver is enabled, a low indicates a signal above the detection threshold is being received. The output is high impedance (50Ω) and should only be used to drive a CMOS logic input.

RXD         pin 12
This digital output from the internal data slicer is a squared version of the signal on pin 13 (AF). It may be used to drive external decoders. The data is true data, i.e. as fed to the transmitter.  Output is "open-collector" format with internal 10kΩ pullup to Vcc (pin 17).

AF           pin 13
This is a buffered and filtered analogue output from the FM demodulator. It has a standing DC bias of 1 volts approx.. It is useful as a test point or to drive linear decoders. External load should be >10kΩ // <100pF.

TXD         pin 14
This DC coupled modulation input will accept either serial digital data (0V to Vcc levels) or High level linear signals. Input impedance is >50kΩ.

TX select     pin 15
Active low transmit select. 47kΩ internal pull up to Vcc.

RX select     pin 16
Active low receive select. 47kΩ internal pull up to Vcc.

TX select (pin 15) RX select (pin 16) FUNCTION
1 1 power down (<1µA)
1 0 receiver enabled
0 1 transmitter enabled
0 0 self test loop back

Note: Loop test allows the receivers to monitor the transmitted signal. The receiver will not receive  external signals whilst the TX of the module is enabled.

Vcc    pin 17
+ve supply pin.  +3.0 to +5.5 Volts @ <20mA . The supply must be clean < 20mVP-P ripple. A 2.2mF de-coupling capacitor and 10W series resistor are used internally to filter the supply.

Absolute maximum ratings

Exceeding the values below may cause permanent damage to the module.

Operating temperature -20°C to +70°C
Storage temperature -40°C to +100°C
Vcc (pin 17) -0.3V to +16V
TX, RX select (pins 15, 16) -9V to +16V
All other pins -0.3V to +Vcc
Antenna (pin 2)
±50V DC, +10dBm RF

Performance specifications

(Vcc = 5.0V / temperature = 20°C unless stated)

General pin min. typ. max. units
notes
DC supply
Supply voltage, Vcc (std. version)
17
2.9
3
16
V
Supply voltage, Vcc (BiM2EH)
17
3.7
5
16
V
TX Supply current @ 10mW
17
-
14
-
mA
TX Supply current @ 25mW
17
-
25
-
mA
TX Supply current @ 100mW
17
-
40
-
mA
RX Supply current
17
10
11
17
mA
Note 1
RF centre frequency
-
-
433.92
-
MHz
Antenna port impedance
2
-
50
-
Ω
TX or RX
TX & RX select, high (deselect
15, 16
Vcc-0.5
-
Vcc
V
low (select)
15,16
0
-
0.5
V
Intrenal selct pull-ups
15, 16
-
47
-
kΩ
to Vcc
Balanced code bit rate (-64 version)
12
-
-
64
kbps
Balanced code bit rate (-10 version)
12
-
-
10
kbps
Transmitter section
pin
min.
typ.
max.
units
notes
RF power output (BiM2A)
2
+9
+10
+11
dBm
RF power output (BiM2H)
2
+13
+14
+15
dBm
RF power output (BiM2EH)
2
+19
+20
+21
dBm
TX harmonics / spurious emission
2
-
-55
-40
dBm
Initial centre frequency accuracy
-
-10
0
+10
kHz
FM deviation (peak)
-
±20
±27
±35
kHz
peak
Baseband
Modulation bandwidth @ -3dB std
-
DC
-
35
kHz
Modulation distortion (THD)
-
-
5
10
%
Note 2
TX spectral bandwidth @-40dBc
2
-
-
250
kHz
worst case
TXD input level: high
14
2.8
-
3.0
V
Note 3
low
14
0
-
0.2
V
Note 3
TX power up to full RF
2, 15
-
1
1.5
ms
Note 4
Receiver section
pin
min.
typ.
max.
units
notes
RF/IF
RF sensitivity @ 10dB S/N
2, 13
-
-106
-
dBm
-64 version
RF sensitivity @ 10dB S/N
2, 13
-
-113
-
dBm
-10 version
RF sensitivity @ 1ppm BER
2, 12
-
-100
-
dBm
-64 version
RF sensitivity @ 1ppm BER
2, 12
-
-107
-
dBm
-10 version
RSSI output, no signal
2, 11
0.15
0.25
0.4
V
RSSI output, max indictaion
2, 11
1
1.12
1,25
V
CD threshold, Vcc=5V
2, 11
-92
-98
-
dBm
CD threshold, Vcc=5V
2, 11
-
-96
-
dBm
@ -50dBm
RSSI range
2, 11
-
60
-
dB
IF Bandwidth
-
-
180
kHz
Image rejection (fRF - 21.4MHz)
2
-
40
50
dB
402.0MHz
IF rejection (10.7MHz)
2
100
-
-
dB
LO leakage, conducted
2
-
-117
-110
dBm
Baseband bandwidth @ -3dB
13
0
-
50
kHz
-64 version
Baseband bandwidth @ -3dB
13
0
-
7.8
kHz
-10 version
AF output signal level
13
200
300
400
mV
Note 5
DC offset on AF out
13
0.3
1.0
1.75
V
Note 6
Distortion on recovered AF
13
-
1
10
%
Note 7
Ultimate (S+N)/N, @ -50dBm RF input
13
-
40
-
dB
LOad capacitance, AF & RXD
12, 13
-
-
100
pF
Dynamic timing
RX power up with signal present
Power up to valid RSSI, tPU-RSSI
11
-
1
-
ms
Power up to valid CD, tPU-CD
11
-
1.5
-
ms
Power up to stable RXD output, tPU-RXD
12
-
5
10
ms
-64 version
Power up to stable RXD output, tPU-RXD
12
-
10
30
ms
-10 version
Signal applied with RX on
RSSI response time (rise/fall)
11
-
100
-
µs
Signal to stable RXD, tsig-RXD
12
-
5
10
ms
-64 version
Signal to stable RXD, tsig-RXD
12
-
5
30
ms
-10 version
Allowable time between data transitions
12, 14
15.6
-
1500
µs
-64 version
Allowable time between data transitions
12, 14
0.1
-
15
ms
-10 version
TX power up to full RF
2
-
1
1.5
ms
Note 8

Notes:

  1. Increases at high RF input level (>-20dBm)
  2. See page 6 for further details
  3. For specified FM deviation
  4. Tx select low > full RF output
  5. ±30kHz FM deviation
  6. Min/max at ±50kHz offset
  7. Max at ±50kHz offset
  8. Average, at max. data rate

Application Information

Modulation formats and range extension

The module will produce the specified FM deviation with a 2-level digital input to TXD which toggles between 0V and 3V. Reducing the amplitude of the data input (to the TXD pin) from this value reduces the transmitted FM deviation, typically to ±20-22kHz minimum at 2.7V. The receiver will cope with this quite happily and no significant degradation of link performance should be observed.

TXD is normally driven directly by logic levels but will also accept analogue drive, e.g. 2-tone signalling. In this case it is recommended that TXD (pin 14) should be DC-biased to 1.5V with the modulation AC-coupled and limited to a maximum of 3V peak-to-peak. The instantaneous modulation voltage must not swing below 0V or above 3V at any time if waveform distortion and excessive FM deviation is to be avoided - use a resistive potential divider and/or level shifter to accomplish this if necessary. The varactor modulator in the transmitter introduces some 2nd harmonic distortion which may be reduced if necessary by predistortion of the analogue waveform.

At the other end of the link the AF output (pin 13) can be used to drive an external decoder directly.

Although the module baseband response extends down to DC, data formats containing a DC component are unsuitable and should not be used. This is because frequency errors and drifts between the transmitter and receiver occur in normal operation resulting in DC offset errors on the AF output.

The time constant of the adaptive data slicer in the BiM2A is set at a reasonable compromise to allow the use of low code speeds where necessary whilst keeping settling times acceptably fast for battery-economised operation. RXD output on pin 12 is "true" sense, i.e. as originally fed to the transmitter.

In applications such as longer range fixed links where data speed is not of primary importance, a significant increase in range can be obtained by using the slowest possible data rate together with filtering to reduce the receiver bandwidth to the minimum necessary. In these circumstances the AF output can be used to drive an external filter and data slicer. The AF output waveform on pin 13 is in the same sense as that originally fed to the transmitter, i.e. no inversion takes place.

Expected range

Predicting the range obtainable in any given situation is notoriously difficult since there are many factors involved. The main ones to consider are as follows:

  • Type and location of antennas in use (see below)
  • Type of terrain and degree of obstruction of the link path
  • Sources of interference affecting the receiver
  • "Dead" spots caused by signal reflections from nearby conductive objects
  • Data rate and degree of filtering employed

Assuming the maximum 64kb/s data rate and ¼-wave whip antennas on both transmitter (@10mW) and receiver, the following ranges may be used as a rough guide only:

Cluttered/obstructed environment, e.g. inside a building:  50-75m
Open, relatively unobstructed environment:                    200-300m

It must be stressed, however, that range could be much greater or much less than these figures. Range tests should always be performed before assuming that a particular range can be achieved in any given application.

Antenna considerations and options

The choice and positioning of transmitter and receiver antennas is of the utmost importance and is the single most significant factor in determining system range. The following notes are intended to assist the user in choosing the most effective arrangement for a given application.

Nearby conducting objects such as a PCB or battery can cause detuning or screening of the antenna which severely reduces efficiency. Ideally the antenna should stick out from the top of the product and be entirely in the clear, however this is often not desirable for practical or ergonomic reasons and a compromise may need to be reached. If an internal antenna must be used, try to keep it away from other metal components and pay particular attention to the "hot" end (i.e. the far end), as this is generally the most susceptible to detuning. The space around the antenna is as important as the antenna itself.

Microprocessors and microcontrollers tend to radiate significant amounts of radio frequency hash, which can cause desensitisation of the receiver if its antenna is in close proximity. 433MHz is generally less prone to this effect than lower frequencies, but problems can still arise. Things become worse as logic speeds increase, because fast logic edges are capable of generating harmonics across the UHF range which are then radiated effectively by the PCB tracking. In extreme cases system range can be reduced by a factor of 3 or more. To minimise any adverse effects, situate the antenna and module as far as possible from any such circuitry and keep PCB track lengths to the minimum possible. A ground plane can be highly effective in cutting radiated interference and its use is strongly recommended.

A simple test for interference is to monitor the receiver RSSI output voltage, which should be the same regardless of whether the microcontroller or other logic circuitry is running or in reset.

The following types of integral antenna are in common use:

Quarter-wave 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

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.

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.

Integral antenna summary:

whip
helical
loop
Ultimate performance
***
**
*
Ease of design set-up
***
**
*
Size
*
***
**
Immunity to proximity effects
**
*
***


Figure 4: integral antenna configurations

Note: Where the specified antennas are mounted on the PCB and/or in close proximity to metalwork (module casing, components, PCB tracking etc), the antenna radiation pattern may be seriously affected. Radiated power may be significantly increased in some directions (sometimes by as much as 10dB) and correspondingly reduced in others. This may adversely affect system performance where good all-round coverage is desired.

Care should also be taken to ensure that this effect does not increase the radiated power in any direction beyond that allowed by type approval regulations. Where this occurs the antenna may need to be relocated. In extreme cases a resistive attenuator of appropriate value may be required between the module and antenna.

Type Approval requirements: Europe

The modules comply with the requirements of the R&TTE Directive (including standards EN 300 220-3 and EN 301 489-3) when used in accordance with the information contained herein. The following provisos apply:

1) The modules must not be modified or used outside their specification limits.
2) The modules may only be used to transfer digital or digitised data. Analogue speech and/or music are not permitted.
3) The equipment in which the BiM2A is used must carry all necessary external labelling to meet the requirements of the R&TTE directive.
4) The BiM2A has not been tested with antennas having gains greater than that of a quarter-wave whip. The use of such antennas may require further R&TTE approval.

Module mounting consideration

Good RF layout practice should be observed. In particular, any ground return required by the antenna or feed should be connected directly to the RF GND pins at the antenna end of the module, and not to the OV pins which are intended as DC grounds only. All connecting tracks should be kept as short as possible to avoid any problems with stray RF pickup.

If the connection between module and antenna does not form part of the antenna itself, it should be made using 50W microstrip line or coax or a combination of both. It is desirable (but not essential) to fill all unused PCB area around the module with ground plane.

Variants and ordering information

The BiM2A/BiM2H receivers are manufactured in several variants:

Data rate:  Slower version: 7.8kHz baseband B/W, data rate up to 10kb/s (suffix -10)
Faster version: 50kHz baseband B/W, data rate up to 64kb/s (suffix -64)

Frequency: 433.92MHz (suffix -433)
434.42MHz (suffix -434)

For European applications in the 433.05 - 433.79870MHz band:
Standard Frequency = 433.92MHz

Part number RF power Data rate TXD input level
CD versions
BiM2A-433-10-CD-3V +10dBm 10kbps 0 - 3V
BiM2A-433-64-CD-3V +10dBm 64kbps 0 - 3V
BiM2A-433-10-CD-5V +10dBm 10kbps 0 - 5V
BiM2A-433-64-CD-5V +10dBm 64kbps 0 - 5V
RSSI versions
BiM2A-433-10 +10dBm 10kbps 0 - 3V
BiM2A-433-64 +10dBm 64kbps 0 - 3V
BiM2H-433-10 +14dBm 10kbps 0 - 3V
BiM2H-433-64 +14dBm 64kbps 0 - 3V
BiM2EH-433-10 +20dBm 10kbps 0 - 3V
BiM2EH-433-64 +20dBm 64kbps 0 - 3

Note: Non-standard frequency variants can be supplied to individual customer requirements. Minimum order quantities apply. Please consult the Sales department for further information.

Limitation of liability

The information furnished by Radiometrix Ltd is believed to be accurate and reliable. Radiometrix Ltd reserves the right to make changes or improvements in the design, specification or manufacture of its subassembly products without notice. Radiometrix Ltd does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. This data sheet neither states nor implies warranty of any kind, including fitness for any particular application. These radio devices may be subject to radio interference and may not function as intended if interference is present. We do NOT recommend their use for life critical applications.
The Intrastat commodity code for all our wireless modules is: 8542 6000.

R&TTE Directive

After 7 April 2001 the manufacturer can only place finished product on the market under the provisions of the R&TTE Directive. Equipment within the scope of the R&TTE Directive may demonstrate compliance to the essential requirements specified in Article 3 of the Directive, as appropriate to the particular equipment.
Further details are available on The Office of Communications (Ofcom) web site:
Licensing policy manual