LMT1/LMR1

VHF Narrow Band FM Low Cost multi channel radio modules

 

The LMT1 transmitter and LMR1 receiver modules offer a multi channel, low power, and reliable VHF data link. This makes the LMT1/LMR1 pair ideally suited to those low power applications where existing wideband modules have insufficient range, or where low cost multi-channel operation is needed without compromising on RF specification or regulatory requirement.

Features

  • Conforms to EN 300 220-3 and EN 301 489-3
  • High performance double superhet, PLL synthesizer with TCXO
  • quasi-dc (peak sampling) data recovery circuit (for enhanced performance on unbalanced datastreams)
  • Data rates up to 5 kbps for standard module
  • Usable range over 1km
  • Fully screened. Low profile
  • Feature-rich interface (RSSI, analogue and digital baseband)
  • 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
  • DGPS systems
  • Vehicle data up/download
  • Heavy vehicle/machinery controls

Technical Summary

  • Operating frequency: 173.200 - 173.325MHz (UK band)
    150.825 - 152.450MHz (Australian Band)
  • Other VHF frequencies available·
  • 4 UK allocation channels (32 maximum)
  • 32 channels
  • Transmit power: +10dBm (10mW) nominal @ 3.1V (Adjustable 1 - 25mW)
  • Supply range: 3.1 - 15V (TX @ 10mW and RX), 4.1 - 15V (TX @ 100mW)
  • Current consumption: 34mA @ 10mW, 90mA @ 100mW (transmit) and 20mA (receive)
  • Data bit rate: 5kbps max. (standard module)
  • Receiver sensitivity -118dBm (for 12dB SINAD)
  • Serial configuration by inverted RS232 at 3V CMOS level

Evaluation Platform: Narrow Band Evaluation Kit


Figure 2: LMT1 block diagram


Figure 3: LMT1 Footprint (Top view)

Pin Description - LMT1

Pin
Name
Function
1a
Vcc 3.1 - 15V power supply (@ 10mW)
4.1 - 15V power supply (@ 100mW)
2a
0V Ground
3a
TXE Transmit Enable (active low)
4a
TXD DC coupled input for 3V CMOS logic. Rin=47kW
5a
No pin Not present in LMT1
1b
P0/PGM
Parallel Channel select LSBSerial frequency programming / configuration1
2b
P1 Parallel Channel select
3b
P2 Parallel Channel select
4b
P3 Parallel Channel select MSB
5b
No pin Not present in LMT

NOTES:

1. Serial programming is by an inverted, CMOS logic level, 2400 baud RS232 datastream applied to the P0 pin.
2. Channel select inputs have pullups (50K) to 3v internal rail. Do not exceed 3V logic levels on this port.
3. Channel select inputs are active low
4. TXE has a 100K pullup to Vcc
5. All pins are on an 0.1" grid
6. The pins 5a/b are not present, but are included in footprint for compatibility with other units in this family
7. In the 'off' state a PIN switch open circuits the RF output pin. There are no 'off' state spuri.
8. 10mW unit will operate (with marginally reduced specifications and lower (6-8mW) output power) from a 3.0V rail. This must be well regulated and without noise or ripple, as in this state the unit's internal regulator no longer operates, and provides no supply rejection.
9. 100mW versions should not be run continuously from supply voltages > 9v


Figure 4: LMR1 block diagram


Figure 5: LMR1 Footprint (Top view)

Pin Description - LMR1

Pin
Name
Function
1a Vcc 3.1 - 15V power supply
2a 0V Ground
3a RXE Receiver Enable (active high)
4a RXD Data out (open collector, no pullup)
5a AF out 700mV p-p audio. DC coupled, approx 0.8v bias.
1b
P0/PGM
Parallel Channel select LSBSerial frequency programming / configuration1
2b P1 Parallel Channel select
3b P2 Parallel Channel select
4b P3 Parallel Channel select MSB
5b RSSI DC level between 0.5v and 2.2v. 60dB dynamic range

NOTES:

1. Serial programming is by an inverted, cmos logic level, 2400 baud RS232 datastream applied to the P0 pin.
2. Channel select inputs have pullups (50kW) to 3v internal rail. Do not exceed 3v logic levels on this port.
3. Channel select inputs are active low
4. All pins are on an 0.1" grid
5. Data recovery circuit used for RXD is not a simple 'average and compare' type. It is a peak sampling quasi-DC coupled design, allowing a greater than usual flexibility in data format.
6. Unit will operate (with maginally reduced specifications) from a 3.0v rail. This must be well regulated and without noise or ripple, as in this state the unit's internal regulator no longer operates, and provides no supply rejection.]

Serial interface commands

LMT1/LMR1 frequency/channel can be serially configured using HyperTerminal or any other terminal program configured with following setup:

2400 baud RS232, 8 bit data, no parity, 1 start bit, 1 or 2 stop bits. No flow control
Serial data is sent to the unit on one of the parallel channel select pins (P0). It is very important that the unit does not 'decode' switch bounce in ordinary operation as a command string, or spurious re-writing of the EEPROM will result. For this reason the user must send the 16 character string ENABLESERIALMODE to fully enable the serial command mode before sending any of the command strings listed below. Command mode is disabled on power down, or on reception of a # character. To successfully program the unit, it must be enabled (RXE high (rx) or TXE low (tx)).

GOCHAN aa Serial select of channel aa (0 to 31)
LOAD aa nnnnn Set value of N register for channel aa, where aa is Channels 0 to 31
RVALUE rrrr Set value for R register
SETPAR Channel selected by 4 bit parallel inputs (ch0 to ch15 only)
SETSER Channel selected by most recent 'GOCHAN' operation
SINGLE nnnnn Set value of N for single channel operation.
N value NOT stored in EEPROM
<cr> Process entry
/ Clear all buffers
# Disable command mode

aa = a two digit channel number from 00 to 31
nnnnn = a synthesizer N register value, (up to 65535)
rrrr = the synthesizer R register value, (up to 16383)

For LMT1 transmitter:

For LMR1 receiver:

, So R = 520

Notes:
1. A pause of at least 50ms must be allowed between command strings (EEPROM programming time).
2. 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.

3. For UK version (173.200 - 173.325MHz band) the following channel assignment is supplied: Channel Frequency (MHz)

Channel
Frequency (MHz)
0
173.250
1
173.275
2
173.300
3
173.325
4 -7
173.225 (only used for alarm applications)
8 -127
173.325

 

Condensed specifications

Frequency Any frequency in the 173MHz and 151MHz bands
In UK band, only 173.250, 173.275, 173.300 and 173.325 MHz are used as standard
Other custom variants from 130 - 180MHz on any 2MHz band

Frequency stability

+/- 1.5kHz
Channel spacing
25kHz
Number of channels

16 channels controlled by parallel port or 32 via RS232 interface

Operating temperature -20 to +70 °C (Storage -30 to +70 °C)
Spurious radiations Compliant with ETSI EN 300 220-3 and EN 301 489-3
LMT1 Transmitter
Supply
Voltage 3.1V - 15V (1-25mW)
4.1 - 15V (25 - 100mW)
Current 34mA @ 10mW (nominal)
90mA @ 100mW (nominal)
<5mA standby (TXE high or floating)
Output power +10dBm (10mW) ±1dB nominal (factory adjustable 1 - 25mW) and
+20dBm (100mW) ±1dB nominal (factory adjustable 25 - 100mW)
TX on switching time 30ms from TXE transition
Peak FM deviation ±3kHz (±1.5kHz @ 12.5kHz channel spacing)
Modulation type FSK (F3D)
TX modulation bandwidth DC - 5kHz (3V CMOS compatible)
Adjacent channel TX power -37dBm
TX spurious <-40dBm (no RF output in Standby)
Inputs data (CMOS/TTL compatible)
Size 33 x 23 x 9mm
Interface
User 10 (8) pin 0.1" pitch dual row (5+5) header
RF 2pin .1" pitch
Recommended PCB hole size 1.2mm
LMR1 Receiver
Sensitivity -118dBm for 12 dB SINAD
S/N ratio 35dB (min), 40dB (typ) on AF output
AF bandwidth (-3dB) 4kHz
image < -60dB
other spurious <-70dBm
blocking better than 84dB
LO re-radiation -70dBm
adj. Channel better than -60dB (Tested per. ETSI EN 301 489-3)
Supply
Voltage 3.1V - 15V
Current 20mA; <1mA standby (RXE low)
outputs RSSI, audio, digital data (quasi DC data recovery circuit)
Size 46 x 23 x 9 mm
Interface
User 10 pin 0.1" pitch dual row (5+5) header
RF 2pin 0.1" pitch molex
Recommended PCB hole size 1.2mm
Dynamic timing
RXE high/active to RX AF stable 25ms
RXE high/active RX data stable
40ms
RX data recovery settling time 20ms
Power on to stable (50:50 mark / space) RXD 50ms (TXE low/active to stable RX data out)
Maximum time between data transitions 250m

 

RX Received Signal Strength Indicator (RSSI)

The LMR1 has wide range RSSI which measures the strength of an incoming signal over a range of 60dB or more. This allows assessment of link quality and available margin and is useful when performing range tests.

The output on pin 5b of the module has a standing DC bias of up to 0.5V with no signal, rising to 2.5V at maximum indication (RF input levels of -40dBm and above). DVmin-max is typically 2V and is largely independent of standing bias variations. Output impedance is 40kW. Pin 5b can drive a 100mA meter directly, for simple monitoring.

Typical RSSI characteristic is as shown below:


Figure 6: RSSI level with respect to received RF level at LMR1 antenna pin

Antenna requirements

Three types of integral antenna are recommended and approved for use with the module:

A) Whip: This is a wire, rod, PCB track or combination connected directly to RF pin 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

B) Helical: Wire coil, connected directly to RF pin, 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.

C) Loop: A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed from RF pin at a point 20% from the ground end. Loops have high immunity to proximity de-tuning.

A
B
C
Whip
Helical
Loop
Ultimate performance
***
**
*
Easy of design set-up
***
**
*
Size
*
***
**
Immunity proximity effects
*
**
***
Range open ground to similar antenna
500
200
100

The antenna choice and position directly controls the system range. Keep it clear of other metal in the system, particularly the 'hot' end. The best position by far, is sticking out the top of the product. This is often not desirable for practical/ergonomic reasons thus a compromise may need to be reached. If an internal antenna must be used, try to keep it away from other metal components, particularly large ones like transformers, batteries and PCB tracks/earth plane. The space around the antenna is as important as the antenna itself.


Figure 7: Antenna types

Ordering Information

Part No. Description RF power (mW) Frequency band (MHz)
LMT1-173-5 Tansmitter 10 173.225- 173.325
LMR1-173-5 Receiver - 173.225- 173.325
LMT1-151-5 Transmitter 100 150.825 - 152.450
LMR1-151-5 Receiver - 150.825 - 152.450
LMT1-xxx-5
LMR1-xxx-5 Where xxx is any 2MHz band from 130MHz to-180MHz 10 / 100

 

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