TX2A/RX2A

UHF FM data transmitter and receiver modules

The TX2A and RX2A data link modules are a miniature PCB mounting UHF radio transmitter and receiver pair which enable the simple implementation of a data link at up to 64 kbps at distances up to 75 metres in-building and 300 metres open ground.

Features

  • CE certified by independent Notified Body
  • Verified to comply with harmonised radio standard EN 300 220-3 and EMC standard EN 301 489-3 by accredited Test Laboratory
  • Data rates up to 64 kbps
  • Usable range up to 300 m
  • Versions available on 433.92MHz and 434.42MHz
  • Fully screened

Available for operation at 433.92MHz or 434.42MHz in the UK and Europe, both modules combine full screening with extensive internal filtering to ensure EMC compliance by minimising spurious radiations and susceptibilities. The TX2A and RX2A modules will suit one-to-one and multi-node wireless links in applications including car and building security, EPOS and inventory tracking, remote industrial process monitoring and computer networking. Because of their small size and low power requirements, both modules are ideal for use in portable, battery-powered applications such as hand-held terminals.

Technical Summary

Transmitter - TX2A

  • Crystal-locked PLL, FM modulated at up to 64 Kbps
  • Operation from 2.2V to 16V (Dependent on version)+10dBm on 433.92MHz
  • High efficiency, >30%, DC to RF
  • Improved frequency and deviation accuracy
  • 2nd harmonic, > -60dBc

Receiver - RX2A

  • Single conversion FM superhetSAW front end filter gives >50dB image rejection
  • Operation from 2.7V to 16V @ 12mA
  • Built-in regulator for improved stability and supply noise rejection
  • -101dBm sensitivity @ 1ppm BER, 64kb/s version
  • -108dBm sensitivity @ 1ppm BER, 10kb/s version
  • RSSI output with 60dB range
  • Extremely low LO leakage, <-100dBm
  • Evaluation Platform: Universal Evaluation kit or Narrow Band Evaluation Kit

Functional description

The TX2A transmitter module is a crystal based PLL controlled FM transmitter operating between 2.2V and 16V and is available in 433.92MHz. The TX2A module is type approved to EN 300 220-3 for European use and delivers nominally +10dBm at 11mA. The module measures 32 x 12 x 3.8 mm.

The RX2A module is a single conversion FM superhet receiver capable of handling data rates of up to 64kbps. It will operate from a supply of 2.7V to 16V and draws 10mA when receiving. The RX2A features a fast power-up time for effective duty cycle power saving and a signal strength (RSSI) output with 60dB of range. Full screening and a SAW front-end filter give good immunity to interference. The SIL style RX2A measures 48 x 17.5 x 4.5 mm excluding the pins.

TX2A transmitter


Figure 2: TX2A block diagram


Figure 3: TX2A pinouts and dimension

Pin Description -TX2A

Pin
Name
Function
1& 3 RF GND RF ground, internally connected to the module screen and pin 6 (0V). These pins should be directly connected to the RF return path - e.g. coax braid, main PCB ground plane etc.
2 RF IN 50Ω RF output to the antenna. Internally DC-isolated. See antenna section of apps notes for details of suitable antennas
4 EN Tx enable. <0.15V shuts down module (current <1mA). >1.7V enables the transmitter. Impedance ~1MΩ. Observe slew rate requirements (see apps notes)
5 Vcc +2.2V to +16V DC supply. Max ripple content 0.1VP-P. Decoupling is not generally required
6 0V DC supply ground. Internally connected to pins 1 & 3 and module screen
7 TXD DC-coupled modulation input. Accepts serial digital data at 0V to 2.5V levels.
See applications notes for suggested drive methods. Input is high impedance (>100kΩ)

Notes:
1. The 3V and 5V supply variant TX2As intended for direct replacement to our SAW based TX2 modules and do not have internal regulator. They also have identical pin out as of TX2, hence lack pin 3 (GND) and pin 4 (Enable).
2. The TXD input of 3V and 5V versions require serial digital data at 0-Vcc levels. i.e. 0-3V and 0-5V respectively

RX2A receiver


Figure 4: RX2A block diagram


Figure 5: RX2A physical dimensions

Pin Description - RX2A

Pin
Name
Function
1 RF IN 50Ω input from the antenna. DC isolated
2 RF GND RF ground pin, internally connected to the module screen and pin 4 (0V). This pin should be connected to the RF return path (coax braid, main PCB ground plane etc.)
3 RSSI Received signal strength indicator with 60dB range. See page 4 for typical characteristics
4 0V DC supply ground. Internally connected to pin 2 and module screen
5 Vcc +2.7V to +16.0V DC supply. Max ripple content 0.1Vp-p. Decoupling is not generally required
6 AF out Buffered and filtered analogue output from the FM demodulator. Standing DC bias 1.1V approx. External load should be >10kΩ // <100pF
7 RXD

Digital output from the internal data slicer. The data is a squared version of the signal on pin 6 (AF) and is true data, i.e. as fed to the transmitter. Output is "open-collector" format with internal 10kΩ pull-up to Vcc (pin 5

Absolute maximum ratings

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

Operating temperatutre - 20°C to +70°C
Storage temperatutre -40°C to +100°C
TX2A all variants
Vcc (pin 3 -0.3V to +16.0V
Data input (pin 5) ± 7V
RF out (pin 2 ±50V DC 10dBm RF
RX2A all variants
Vcc(pin5) -0.1V to +16V
RSSI, AF, RXD (pins 3,6,7) -0.1V to + 3V
RF IN (pin 1) ±50V DC, +10dBm R

Performance specifications:TX2A

(Vcc = 5.0V / temperature = 20ºC unless stated)

pin

min.

typ.

Max.

units

notes

DC supply
Supply voltage 3 2.2 3.0 4.0 V -3V version
Supply voltage 3 4.0 5.0 6.0 V -5V version
Supply voltage 3 3 - 16 V STD
Current & RF Power
TX2A all variants
supply current 3
9
11
13
mA
RF power
2
+8
+10
+12
dBm
1
RF
2nd harmonic
2
-
-70
-54
dBc
1
Harmonics @ >1GHz
2
-
-60
-40
dBc
1
Initial frequency accuracy
-
-20
+/-10
+20
kHz
overall frequency accuracy
-
-25 +/-10 +25 kHz
Peak FM deviation
±20
±27
±35
kHz
Baseband
Modulation bandwidth @ -3dB 0
-
35 kHz
Modulation distortion (THD)
-
5
10 %
Dynamic timing
Power-up time (En --> full RF)
-
1.0 1.5 ms

Notes:
1. Measured into a 50Ω resistive load.

Performance specifications: RX2A

(Vcc = 5.0V / temperature = 20ºC unless stated)

pin
min.
typ.
max.
units
notes
DC supply
Voltage
5
2.7
5
16
V
Ciurrent
5
9
10
18
mA
1
RF/IF
RF sensitivity for 10dB (S+N/N)
1, 6
-
-115
-
dBm
10kbps version
RF sensitivity for 10dB (S+N/N)
1, 6
-
-108
-
dBm
64kbps version
RF sensitivity for 1ppm BER
1, 6
-
-108
-
dBm
10kbps version
RF sensitivity for 1ppm BER
1, 6
-
-101
-
dBm
64kbps version
RSSI range
1, 3
-
60
-
dB
IF bandwidth
-
-
180
-
kHz
Image rejection
1
50
54
-
dB
½-IF spurious rejection
1
100
-
-
dB
IF rejection (10.7MHz)
1
100
-
-
dB
LO leakage, conducted
1
-
-125
-110
dBm
Baseband
Baseband bandwidth @ -3dB
6
0
-
7.8
kHz
10kbps version
Baseband bandwidth @ -3dB
6
0
-
50
kHz
64kbps version
AF level
6
350
450
550
mVp-p
2
DC offset on AF out
6
0.45
1.1
1.75
V
3
Distortion on recovered AF
6
-
1
10
%
3
Ultimate (S+N)/N
6
-
40
-
dB
Load capacitance, AFout/RXD
6, 7
-
-
100
pF
DYNAMIC TIMING
Power up with signal present
Power up to valid RSSI
3, 5
-
1
-
ms
Power up to stable data
5, 7
-
10
30
ms
3, 10kbps version
Power up to stable data
5, 7
-
5
10
ms
3, 64kbps version
Signal applied with supply on
RSSI response time (rise/fall)
1, 3
-
100
-
ms
Signal to stable data
1, 7
-
5
30
ms
3, 10kbps version
Signal to stable data
1, 7
-
5
10
ms
3, 64kbps version
Time between data transitions
7
0.1
-
15
ms
4, 10kbps version
Time between data transitions
7
15.6
-
1500
ms
4, 64kbps version
Mark:space ratio
7
20
50
8

Notes: 1. Current increases at higher RF input levels (>-20dBm and above).
2. For received signal with ±40kHz FM deviation
3. Typical figures are for signal at centre frequency, max. figures are for ±50kHz offset
4. For 50:50 mark to space ratio (i.e. squarewave)
5. Average over 30ms (10kbps version) or 3ms (64kbps version) at maximum data rate

Power supply requirements

The standard TX2A and the RX2A modules incorporate a built-in regulator which delivers a constant 2.8V to the module circuitry when the external supply voltage is 2.85V or greater, with 40dB or more of supply ripple rejection. This ensures constant performance up to the maximum permitted supply 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).

Note, however, that for supply voltages lower than 2.85V the regulator is effectively inoperative and supply ripple rejection is considerably reduced. Under these conditions the ripple/noise on the supply rail should be below 10mVp-p to avoid problems. If the quality of the supply is in doubt, it is recommended that a 10mF low-ESR tantalum or similar capacitor be added between the module supply pin (Vcc) and ground, together with a 10Ω series feed resistor between the Vcc pin and the supply rail.
The Enable pin allows the module to be turned on or off under logic control with a constant DC supply to the Vcc pin. The module current in power-down mode is less than 1mA.

NOTE: If this facility is used, the logic control signal must have a slew rate of 40mV/ms or more. Slew rates less than this value may cause erratic operation of the on-board regulator and therefore the module itself.

The TX2A incorporates a low voltage shutoff circuit which prevents any possibility of erratic operation by disabling the RF output if the supply voltage drops below 2.2V (±5%). This feature is self-resetting, i.e. restoring the supply to greater than 2.2V will immediately restore full RF output from the module.

TX2A modulation requirements

The module will produce the specified FM deviation with a TXD input to pin 7 of 2.5V amplitude, i.e. 0V "low", 2.5V "high". Reducing the amplitude of the data input from this value (usually as a result of reducing the supply voltage) reduces the transmitted FM deviation to typically ±25kHz at the lower extreme of 2.2V. The receiver will cope with this quite happily and no significant degradation of link performance should be observed as a result.

Where standard 2-level digital data is employed with a logic "low" level of 0V ±0.2V, the logic "high" level applied to TXD may be any value between +2.5V and +3V for correct operation. However, if using multi-level or analogue signalling the maximum positive excursion of the modulation applied to TXD must not exceed +2.5V or waveform distortion will result. If the input waveform exceeds this level a resistive potential divider should be used at the TXD input to reduce the waveform amplitude accordingly. This input is high impedance (>100kW) and can usually be ignored when calculating required resistor values.

Data formats and range extension

The TX2A data input 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 7) be DC-biased to 1.25V with the modulation ac-coupled and limited to a maximum of 2.5Vp-p to minimise distortion over the link. The varactor modulator in the TX2A 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 RX2A AF output is used to drive an external decoder directly.

Both the AF output on pin 8 and the RXD output on pin 9 of the RX2A are "true" sense, i.e. as originally fed to the transmitter.

Although the modulation bandwidth of the TX2A extends down to DC, as does the AF output of the RX2A, it is not advisable to use data containing a DC component. This is because frequency errors and drifts between the transmitter and receiver occur in normal operation, resulting in DC offset errors on the RX2A audio output.

The RX2A incorporates a low pass filter which works in conjunction with similar filtering in the TX2A to obtain an overall system bandwidth of 32kHz. This is suitable for transmission of data at raw bit rates up to 10kbps and 64kbps, depending on the receiver version. To keep settling times within reasonable limits for the data speed in use, the adaptive data slicer in the RX2A is subject to a maximum time limit between data transitions (see page 5). This limitation must be taken into account when choosing a code format. It is strongly recommended that a reasonably balanced code containing no long 1s or 0s (such as Manchester or similar) is employed.

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, because of the limitations of the internal data slicer it is better to use the RX2A audio output to drive an external filter and data slicer.

Received Signal Strength Indicator (RSSI)

The module incorporates a wide range RSSI which measures the strength of an incoming signal over a range of approximately 60dB. This allows assessment of link quality and available margin and is useful when performing range tests.

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.

The output on pin 3 of the module has a standing DC bias of 0.15V-0.45V (0.25V typ.) with no signal, rising to 0.9-1.3V (1.15V typ.) at maximum indication. The RSSI output source impedance is high (~50kΩ) and external loading should therefore be kept to a minimum.

To ensure a fast response the RSSI has limited internal decoupling of 1nF to ground. This may result in a small amount of ripple on the DC output at pin 3 of the module. If this is a problem further decoupling may be added at the expense of response speed, in the form of a capacitor from pin 3 to ground. For example, adding 10nF here will increase RSSI response time from 100µs to around 1ms. The value of this capacitor may be increased without limit.

Typical RSSI characteristic is shown below (this is for indicative purposes only and is not a guarantee of actual RSSI characteristics):


Figure 6: Typical RSSI response curve

Module mounting considerations

The module may be mounted vertically or bent horizontal to the motherboard. 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 pin at the antenna end of the module, and not to the 0V pin which is intended as a DC ground 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 50Ω 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.

The module may be potted if required in a viscous compound which cannot enter the screen can.

Warning: DO NOT wash the module. It is not hermetically sealed.

Variants and ordering information

The TX2A is manufactured in several variants depending on their supply voltage and operating frequency:

Supply voltage:

3V version:  TX2A-433-64-3V Direct replacement for the TX2-433-40-3V
5V version:  TX2A-433-64-5V Direct replacement for the TX2-433-40-5V
Standard:    TX2A-433-64 Different frequency replacement for TX3A

The standard frequency is 433.92MHz, for other frequency variants, please contact sales department.

The RX2A receiver is manufactured in several variants depending on the :

Data rate:

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

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

The following variants are standard:

RX2A-433-10 (433.92MHz, 10kbps)
RX2A-433-64 (433.92MHz, 64kbps)

For other variants please contact our Sales Department

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 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