Hartcran House, 231 Kenton Lane, Harrow, Middlesex, HA3 8RP, England
Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233, www.radiometrix.com
PRELIMINARY
WRX2
433.92MHz Low Cost FM Receiver
The WRX2 is a low cost wide band FM
receiver in a Radiometrix SIL standard pin
out and footprint. It offers an economical and
reliable low power data link without
compromising the receiver performance.
WRX2 receiver and the matching TX2A
transmitter enable the simple implementation
of a wireless data link at up to 12 kbps at
distances up to 75 metres in-building and
300 metres open ground.
Issue A, 11 November 2009
Figure 1: WRX2-433-12
Features
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Conforms to ETSI EN 300 220-3 (radio) and EN 301 489-3 (EMC)
Standard frequencies: 433.92MHz
Custom frequencies available in 433MHz (EU) band
Data rates up to 12kbps
Usable range over 300m
Technical Summary
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Double conversion FM superhet
SAW band pass filter, image rejection: 45dB
Supply range: +3V or 2.9V - 15V (regulator version) @ 22mA
Data bit rate: 12kbps max.
Receiver sensitivity: -115dBm (for 12dB SINAD)
Local Oscillator (LO) re-radiation: <-65dBm
Adjacent Channel: -65dBm
Blocking: -75dB
Size: 47 x 17 x 6 mm (47 x 17 x 8.5mm with can)
Applications
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Handheld terminals
EPOS and inventory tracking
Sensor nodes
Data loggers
Industrial telemetry and telecommand
In-building environmental monitoring and control
High-end security and fire alarms
Evaluation platforms:
Universal Evaluation Kit, NBEK + SIL carrier
Radiometrix Ltd.,
WRX2 data sheet
Page 1
WRX2 receiver
Figure 2: WRX2 block diagram
47mm
8.5mm
17mm
WRX2
Radiometrix
30.48mm (1.2")
1
2
3
4
5
6
7
7 holes of 0.7mm dia pin spacing 2.54mm (0.1")
1 = RF in
2 = RF gnd
3 = RSSI
4 = 0V
5 = Vcc
6 = AF
7 = RXD
Figure 3: WRX2 pin-out and dimension (with can)
User interface
WRX2 pin
1
2
3
4
5
6
7
Name
RF in
RF gnd
RSSI
0V
Vcc
AF
RXD
Function
50Ω RF input from the antenna
RF Ground is internally connected to the module screen and pin 4 (0V).
These pins should be directly connected to the RF return path - e.g. coax
braid, main PCB ground plane etc.
Received Signal Strength Indicator with >60dB range.
DC level between 0.3V and 1.5V
Ground
2
2.9 – 15V DC power supply
600mV
pk-pk
audio. DC coupled, approx 1.4V bias
Received Data output from the internal data slicer. The data is squared
version of the Audio signal on pin 6 and is true data, i.e. as fed to the
transmitter. Output is "open-collector" format with internal 10kΩpull-up to
Vcc (pin 5). Suitable for bi-phase codes
Notes:
1. Pin out is as RX2A receiver
2. The unit can be offered in regulated (2.9 to 15v) or the cheaper +3v only (no regulator fitted)
versions
3. The standard version has no can, and mounts vertically on Batten and Allen leadframe pins. A
second version is for horizontal mounting with square header pins and an NRX2 case fitted
4. Standard version is 6mm thick. The horizontal (canned) unit is 8.5mm
Radiometrix Ltd.,
WRX2 data sheet
Page 2
Absolute maximum ratings
Exceeding the values given below may cause permanent damage to the module.
Operating temperature
Storage temperature
Vcc, RXD (pins 5, 7)
RSSI, AF (pins 3, 6)
RF in (pin 1)
-20°C to +55°C
-30°C to +80°C
-0.3V to +16.0V
-0.3V to +Vcc V
±50V
@ <10MHz, +13dBm @ >10MHz
Performance specifications
(Vcc = 3V / temperature = 20
°
C unless stated)
pin
DC supply
Supply voltage
Supply current
RF/IF
RF centre frequency
Frequency stability
Channel spacing
Number of channels
RF sensitivity @ 12dB SINAD
RSSI range
Blocking
Image rejection
Adjacent channel rejection
Spurious response rejection
LO re-radiation
Baseband
Baseband bandwidth @ -3dB
AF level
DC offset on AF out
Distortion on recovered AF
Dynamic timing
Power up with signal present
Power up to valid RSSI
Power up to valid AF
Power up to stable data
Signal applied with supply on
Signal to valid RSSI
Signal to valid AF
Signal to stable data
min.
typ.
max.
units
notes
4, 5
4, 5
2.9
-
3.0
22
15
-
V
mA
1, 6
1, 6
1, 3
1
1
1
1
1
-
-
-
-
-
-
-
-
-
-
-
433.92
±10
350
1
-115
60
75
50
70
55
-
-
-
-
-
-
-
-
-
-
-
-65
MHz
KHz
KHz
dBm
dB
dB
dB
dB
dB
dBm
1
2
3
4
6
6
6
6
0
-
-
-
-
600
1.4
2
6
700
-
5
kHz
mV
P-P
V
%
5
6
5, 4
5, 6
5, 7
-
-
3
2
TBA
-
10
ms
ms
ms
1, 4
1, 6
1, 7
-
-
2
1
TBA
-
5
ms
ms
ms
7
Time between data transitions
7
0.1
-
TBA
ms
Notes:
1. 433.92MHz is standard, other UHF 431-437MHz by special order
2. for 12 dB SINAD / 1KHz @ 30KHz deviation
3. See applications information for further details
4. Exceeds EN/EMC requirements at all frequencies.
5. -3dB bandwidth @ 12kbps NRZ data rate
6. For received signal with
±30kHz
FM deviation. AF output is inverted with respect to TXD input.
7. For 50:50 mark to space ratio (i.e. squarewave).
Radiometrix Ltd.,
WRX2 data sheet
Page 3
Applications information
Power supply requirements
WRX2 modules have built-in regulator which deliver a constant 2.8V to the module circuitry when the
external supply voltage is 2.9V or greater, with 40dB or more of supply ripple rejection. 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 >100mV
pk-pk
).
WRX2 Received Signal Strength Indicator (RSSI)
The WRX2 receiver incorporates a wide range RSSI which measures the strength of an incoming signal over
a range of 60dB. This allows assessment of link quality and available margin and is useful when performing
range tests.
The output on pin 3 of the module has a standing DC bias of 0.3V with no signal, rising to around 1.5V at
maximum indication (saturation point @ -60dBm).
Typical RSSI characteristic is as shown below:
Figure 4: RSSI response curve
Please note that the actual RSSI voltage at any given RF input level varies somewhat between units. The
RSSI facility is intended as a relative indicator only - it is not designed to be, or suitable as, an accurate
and repeatable measure of absolute signal level or transmitter-receiver distance.
Radiometrix Ltd.,
WRX2 data sheet
Page 4
Antennas
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 antenna type for any given application.
Integral antennas
These are relatively inefficient compared to the larger externally-mounted types and hence tend to be
effective only over limited ranges. They do however result in physically compact equipment and for this
reason are often preferred for portable applications. Particular care is required with this type of antenna to
achieve optimum results and the following should be taken into account:
1. 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/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.
2. 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. The problem becomes
worse as logic speeds increase, because fast logic edges generate harmonics across the UHF range
which are then radiated effectively by the PCB tracking. In extreme cases system range may be reduced
by a factor of 5 or more. To minimise any adverse effects situate 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 consists simply of a piece of wire or rod connected to the module at one end. At
434MHz the total length should be 164mm from module pin to antenna tip including any interconnecting wire
or tracking. Because of the length of this antenna it is almost always external to the product casing.
Helical.
This is a more compact but slightly less effective antenna formed from a coil of wire. It is very
efficient for its size, but because of its high Q it suffers badly from detuning caused by proximity to nearby
conductive objects and needs to be carefully trimmed for best performance in a given situation. The size
shown is about the maximum commonly used at 434MHz and appropriate scaling of length, diameter and
number of turns can make individual designs much smaller.
Loop.
A loop of PCB track having an inside area as large as possible (minimum about 4cm ), tuned and
matched with 2 capacitors. Loops are relatively inefficient but have good immunity to proximity detuning, so
may be preferred in shorter range applications where high component packing density is necessary.
Integral antenna summary:
whip
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*
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helical
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***
*
loop
*
*
**
***
2
Ultimate performance
Ease of design set-up
Size
Immunity to proximity effects
Radiometrix Ltd.,
WRX2 data sheet
Page 5
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