TX2M/RX2M

UHF Narrow Band FM Multi channel radio modules

The RX2M receiver and TX2M transmitter modules offer a low power, reliable data link in an industry-standard pin out and footprint. This makes the TX2M/RX2M pair ideally suited to those low power applications where existing wideband modules have insufficient range, or where multi-channel operation is needed.
Two versions are available, covering the 458.5-459.1MHz UK band (at 100mW) and the European 433.05-434.79MHz band.

Features

  • 433MHz version conforms to EN 300 220-3 and EN 301 489-3 and 458MHz version to MPT 1329 (UK specs)
  • Any custom band between 420MHz and 480MHz with 5MHz (AR0) frequency range
  • High performance double superhet, 128 channel PLL synthesizer with TCXO
  • Data rates up to 5 kbps for standard module
  • Usable range over 1km
  • Fully screened. Low profile
  • Feature-rich interface (RSSI, noise squelch, analogue and digital baseband)
  • Incorporate a 1200baud dumb modem
  • Re-programmable via RS232 interface
  • Low power requirements

Applications

  • Handheld terminals
  • EPOS equipment, barcode scanners
  • Data loggers
  • Industrial telemetry and telecommand
  • In-building environmental monitoring and control
  • High-end security and fire alarms
  • Vehicle data up/download

Technical Summary

  • Size: 59 x 38 x 7mm
  • Operating frequency: 458.5-459.1MHz or 433.05-434.79MHz
  • 23 channels in 458MHz band (128 channels max.)
  • Transmit power: +20dBm (100mW) nominal
  • Supply range: 4.5V - 16V
  • Current consumption: 100mA transmit, 13mA receive
  • Data bit rate: 5kbps max. (standard module)
  • Receiver sensitivity: -118dBm (for 12dB SINAD)

Figure 1: TX2M block diagram

Figure 3: TX2M Footprint (Top of the unit) view

Pin Description - TX2M

Pin Name Function
Power: A
1 Vcc +4.5V to 16V supply
2 Gnd Ground
RF: B
1 Gnd RF ground
2 RF out To antenna
3 Gnd RF ground
User: C
1 0V Ground
2 TXE Transmitter enable. Low = ON, open = off. 4k7 pullup to raw Vcc
3 TXD DC coupled input for 3-12V CMOS logic. Leave open if unused
4 AF in AC coupled 1V pk-pk +/- 10% Analogue input
5 +4.4Vout DC supply. 75mA max. drain. Only present when TXE is low
6 PGM Serial programming/configuration input at RS232 level
7 0V Ground
8 P1 (mod TXD) Parallel frequency select inputs. Inverted logic, 10k pullups to 4V
9 P2 (mod NC)
10 P3 (mod TXH)

Pin Description - RX2M

Pin
Name
Function
Power: A
1 Vcc +4.5V to 16V supply
2 Gnd Ground
RF: B
1 Gnd RF ground
2 RF in To antenna
3 Gnd RF ground
User: C
1 RSSI DC level between 0.5V and 2.5V. 60dB dynamic range
2 SQF Noise operated carrier detect. Open collector. ON/low = no signal
3 AF out 200mV pk-pk audio. DC coupled, approx 1V bias. Muted by squelch
4 RXD Open collector output of data slicer. Need external pull-up
5 +4.4V out DC supply. 75mA max. drain. Present if unit is powered
6 0V Ground
7 PGM Serial programming/configuration input at RS232 level
8 P1 (mod NC) Parallel frequency select inputs. Inverted logic, 10k pullups to 4V
9 P2 (mod RXD)
10 P3 (mod C

TX2M and RX2M serial interface commands

SINGLE nnnnn set value of N for single channel operation
GOCHAN xx serial select of channel xx (0 to 127)
LOADMX xx set highest permitted (serial selected) channel xx (others default to ch0)
LOAD aa nnnnn set value of N for channel aa (channels 0 to 15)
LOADTB nnnnn set value of N for channel 16 (channels 17 to 127 then in sequence)
RVALUE rrrr enter value for R register
SETPAR channel selected by 3 bit parallel input (0 to 7). Disable modem
SETSER channel selected by most recent 'gochan' operation
SETMOD enable internal modem. Frequency selected by most recent 'GOCHAN' or 'SINGLE'
GOTEST 250Hz test tone transmission
<CR> process entry (Carriage Return = 0D hex )
/ clear all buffer

, So R = 520

Channel number 433MHz band N value for TX N value for RX 458MHz band N value for TX N value for RX
0
433.050 /LOAD00 17322 /LOAD00 16466 458.525 /LOAD00 18341 /LOAD00 17485
1
433.075 /LOAD01 17323 /LOAD01 16467 458.550 /LOAD01 18342 /LOAD01 17486
2
433.100 /LOAD02 17324 /LOAD02 16468 458.575 /LOAD02 18343 /LOAD02 17487
3
433.125 /LOAD03 17325 /LOAD03 16469 458.600 /LOAD03 18344 /LOAD03 17488
4
433.150 /LOAD04 17326 /LOAD04 16470 458.625 /LOAD04 18345 /LOAD04 17489
5
733.175 /LOAD05 17327 /LOAD05 16471 458.650 /LOAD05 18346 /LOAD05 17490
6
433.200 /LOAD06 17328 /LOAD06 16472 458.675 /LOAD06 18347 /LOAD06 17491
7
433.225 /LOAD07 17329 /LOAD07 16473 458.700 /LOAD07 18348 /LOAD07 17492
8
433.250 /LOAD08 17330 /LOAD08 16474 458.725 /LOAD08 18349 /LOAD08 17493
9
433.275 /LOAD09 17331 /LOAD09 16475 458.750 /LOAD09 18350 /LOAD09 17494
10
433.300 /LOAD10 17332 /LOAD10 16476 458.775 /LOAD10 18351 /LOAD10 17495
11
433.325 /LOAD11 17333 /LOAD11 16477 458.800 /LOAD11 18352 /LOAD11 17496
12
433.350 /LOAD12 17334 /LOAD12 16478 458.825 /LOAD12 18353 /LOAD12 17497
13
433.375 /LOAD13 17335 /LOAD13 16479 458.850 /LOAD13 18354 /LOAD13 17498
14
433.400 /LOAD14 17336 /LOAD14 16480 458.875 /LOAD14 18355 /LOAD14 17499
15
433.425 /LOAD15 17337 /LOAD15 16481 458.900 /LOAD15 18356 /LOAD15 17500
16
433.450 /LOADTB 17338 /LOADTB 16482 458.925 /LOADTB 18357 /LOADTB 17501
F max
434.775 /LOADMX 69 /LOADMX 69 459.100 /LOADMX 23 /LOADMX
Frequency Band ERP Duty Cycle Channel spacing
E (433.050 - 434.790MHz) 10mW <10% No spacing
E1 (433.050 - 434.790MHz) 1mW <100% No spacing
E2 (434.040 - 434.790MHz) 10mW <100% <25kH

Figure 6: Maximum allowed and programmable channels
Notes
1. A pause of at least 50ms must be allowed between command strings (EEPROM programming time) SINGLE mode does not store the N value in EEPROM. Therefore the unit is inoperative after a power down until either another valid SINGLE command is received, or mode is changed by a GOCHAN, SETPAR or SETSER command. SINGLE mode is intended for frequency agile applications.

2. /SETPAR command should be issued at the end of channel programming to put the module back into parallel frequency select mode

3. In 458MHz band, channel 12 (458.825MHz) and channel 15 (458.900MHz) are allocated specifically for fixed alarm and radio keys/vehicle paging applications respectively and should not be used for general purpose applications.

Pin description of TX2M/RX2M with Modem mode selected

Pin Description - TX2M

Pin
Name
Function
1 0V Ground
2 TXE Must be tied to 0V
3 N/C
4 N/C
5 +4.4Vout DC supply. 75mA maximum drain. Only present when TXE is low
6 PGM Serial programming/configuration input at RS232 level
7 0V Ground
8 MOD TXD (P1) Serial data input at RS232 level
9 MOD N/C (P2)
10 MOD TXH (P3) Active Low Transmit Hold for continuous transmission (useful for test)

Pin Description - RX2M

Pin
Name
Function
1 RSSI DC level between 0.5V and 2.5V. 60dB dynamic range (only valid during databursts)
2 N/C
3 N/C (modem tones or noise present)
4 N/C (modem tones or noise present)
5 +4.4Vout DC supply. 75mA max. drain. Present if unit is powered
6 0V Ground
7 PGM Serial programming/configuration input at RS232 level
8 MOD N/C (P1)
9 MOD RXD (P2) Modem Received Data at TTL level (requires RS232 driver)
10 MOD CDE (P3) Pull low to enable carrier detect on modem operation (not recommended)

Condensed specifications

Frequency 458.5-459.1MHz or 433-434MHz (or any 5MHz band from 420-480MHz)

Frequency stability

+/- 1.5kHz
Channel spacing
25kHz (12.5kHz by special order)
Number of channels
128 channels controlled via RS232 interface (8 parallel selected)
Supply voltage 4.5V - 16V
Current 100mA nominal transmit
13mA receive
Operating temperature -10 to +60 °C (Storage -30 to +70 °C)
Size 59 x 38 x 7 mm
Spurious radiations Compliant with ETSI EN 300 220-3 and EN 301 489-3
Interface                    user 10pin 0.1" pitch molex

Power

2pin 0.1" pitch molex
RF 3pin 0.1" pitch molex
Recommended PCB hole size 1.2mm
Intended approval ETSI radio standard EN 300 220-3 and EMC standard EN 301 489-3
Transmitter
Output power 100mW +/- 1dB (adjustable 1 - 100mW)
TX on switching time 50 ms
Modulation type FM, FSK (F1D, F3D)
TX modulation bandwidth DC - 3kHz
Adjacent channel TX power -37dBm
Inputs analogue, data (CMOS/TTL compatible)
Receiver
Sensitivity -112dBm for 1 part per 1000BER
-118dBm for 12 dB SINAD
image / spurious -70dB
blocking -85dB
adjacent Channel <-60dB (Tested per. ETSI EN 301 489-3)
re-radiation -57dBm
outputs RSSI, carrier detect, audio, data
Power on to valid audio (no noise mute) 28ms
Power on to valid audio (with noise mute ) 45ms
Power on to stable data out (50:50 mark / space) 50ms (with or without mute

Typical current consumption of TX2M at various RF output power level
RF power (mW)    Current consumption (mA)
100                                 90
50                                   67
25                                   54
10                                   41
5                                     35
1                                     30

Note: These measurements taken at 433MHz (for 458MHz current consumption increases by about 5%)

Operating principle of internal modem

Physically the modem code resides in the PIC microcontroller which controls the radio functions. The modem uses the internal hardware serial port of the processor.

Operation: Serial interface

For transmission across the link data is formatted into packets, each comprising 3 bytes of data and a sync code. If less than 3 bytes are in the transmit end FIFO then a packet is still sent, but idle state replaces the unused bytes. When the transmit end FIFO is completely emptied, then the transmitter is keyed off .

Operation: Radio interface

The radio link is fed a continuous tone by the modem. As in biphase codes, information is coded by varying the duration consecutive half-cycles of this tone. In our case half cycles of 500us (a long, or L) and 250us (a short, or S) are used.

In idle (or 'preamble') state, a sequence of Ls is sent (resembling a 1KHz tone).

A packet comprises the Synchronising (or address) part : LSSSSSSSSSSSSL followed by the Data part, made up of twelve Groups (of four half cycles duration). Each Group encodes 2 data bits, so one byte is encoded by 4 Groups.

Although there are 16 possible states for a four half cycle group (from SSSS to LLLL), only four of the possible states are used for valid data:

All other possible group combinations (except LLLL) are void, and result in the entire packet being rejected by the receiver software as a noise artifact. Idle state tone (LLLL ....) is decoded as null data, but does not void the packet, as a packet containing less than 3 bytes still needs to be decoded.

The advantage of using the above coding technique:

1.Ease of decoding: Unlike biphase, where a bit is coded as either a long half cycle or a short cycle, here all half cycles are detected separately.
2. Inherent error detection: Although only 14 sync/address 'bits' (halfcycles) are used, the following 48 'bits' (halfcycles) only code 24 real data bits, leading to enhanced noise/error discrimination (the equivalent of 5 more sync bits).
3. Comparable spectral efficiency: For a maximum transmitted baseband frequency of 2KHz, a 3 byte packet is sent in 22ms. An equivalent biphase coded packet (comprising 19 sync + 24 data + 3 null flags) at 2kbits/sec takes 23ms

Appendix A

The transmitter is available in two variants - TX2I and TX2M

The non-inverting transmitter called TX2M frequency modulates the carrier frequency in the normal sense whereby higher modulating voltage increases the carrier frequency and lower modulating voltage decreases the carrier frequency which results in an inverted AF and Data output on the receiver. This will be the standard module and exact plug-in replacement for existing industry standard modules.

Figure 7: Data polarity change from TX2M (non-inverting) to RX2M

The inverting transmitter called TX2I reverses the Frequency Modulating order whereby the higher modulating voltage decreases the carrier frequency and lower modulating voltage increases carrier frequency which results in non-inverting AF and Data output on the receiver. This variant can be used for applications where data inversion will be problematic.

Ordering information

Part Number Description Frequency band Maximum data rate
TX2M-433-5 TX2M (non-inverting) transmitter 433.05MHz-434.790MHz 5kbps
TX2I-433-5 TX2I (inverting) transmitter 433.05MHz-434.790MHz 5kbps
RX2M-433-5 RX2M receiver 433.05MHz-434.790MHz 5kbps
TX2M-458-5 TX2M (non-inverting) transmitter 458.525MHz-459.100MHz 5kbps
TX2I-458-5 TX2I (inverting) transmitter 458.525MHz-459.100MHz 5kbps
RX2M-458-5 RX2M receiver 458.525MHz-459.100MHz 5kbps
TX2M-458-10 TX2M (non-inverting) transmitter 458.525MHz-459.100MHz 10kbps
TX2I-458-10 TX2I (inverting) transmitter 458.525MHz-459.100MHz 10kbps
RX2M-458-10 RX2M receiver 458.525MHz-459.100MHz 10kbps

R&TTE Directive