1. TR2M receiver section inverts the sense of the baseband stream, so a logical inversion is present between input of TX and output of RX. A version is available (TR2I) which inverts the transmit datastream as well (resulting in no net inversions between a pair of TR2I radios).

2. Carrier detect on TR2M mutes the AF and RXD outputs. It can be factory disabled.

3. 3. All the open collector outputs must be connected to Vcc/+4.4V out via a pull-up resistor.

4. The software incorporates a 1200baud dumb modem, compatible with that implemented in TX2M, RX2M radios (i1200 tones and format)

5. With 1200baud modem mode enabled, parallel selection of channel is unavailable as the P1-P3 lines are used for input/output operations.

6. 6. PGM and MOD TXD (pin 10 and 11) tolerate true ±RS232 levels. No buffering is required.

TR2M has an automatic noise squelching function which is activated when there is not any RF signal at detectable level on the channel or if the non-coherent noise like interference level is high enough to block any weak RF signal from being received. SQF is provided as an open-collector output for monitoring which should be pulled-up to required voltage swing level. SQF output will jump to pull-up voltage level if received RF signal level at the RF In/Out pin of the module is about 3dB below the level required to produce 12dB SINAD level on demodulated AF Output signal. SQF pin can be connected to an LED to act as a Carrier Detect indicator. Pull-up resistor value should be reduced (e.g. 1kW) according to the current requirement to produce satisfactory brightness on the LED used.

TR2M can be configured using any PC/Laptop/PDA having a serial port and modem/terminal program. TXD (pin 3) of DB9M connector can be directly wired to PGM (pin C10) of the TR2M and SGN (pin 5) of DB9M connector should be either connected to common ground or pin C9 of the TR2M.

The whole frequency/channel table is user reconfigurable to 128 channels within 5MHz band of supplied frequency subject to regulatory band limits. Serial Channel Selection via PGM pin gives access to the whole of regulatory band allocation for 433.05MHz-434.790MHz (69 channels) or 458.525MHz-458.925MHz (23 channels).

RSSI can also be used to make a decision to switch to the second antenna in fixed installations within building where the probability of null-spots are higher.

There is a generic 10% duty cycle restriction on the 433MHz ISM band through out European countries with few exceptions. Annex 1 Band E, Band E2 of European Radio Communications Committee (ERC) Recommendation 70-03 dated February 2004 specifies the following:

TR2M serial interface commands

2400 baud RS232. 8 bit data, no parity, 1 start bit, 1 or 2 stop bits, No flow control

xx = a channel number from 00 to 127
aa = a two digit channel number from 00 to 15
nnnnn = a synthesizer N register value, (up to 65535)
rrrr = the synthesizer R register value, (up to 16383)
000 = frequency offset

Figure 6: Maximum allowed and programmable channels

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.

4. User can modify the frequency table of 128 channels to any desired frequency by changing N, R values of synthesizer within ±2.5MHz of factory set Channel 0 frequency subject to the Radio Regulatory Band Allocation in the country of intended use.

5. All other frequency, power, analogue input gain and automatic noise squelching adjustment will be treated as custom variants of the module to be set by factory.

Transceiver Variants

TR2M is designed to be pin and polarity compatible with existing industry standard modules. Analogue and Digital Data Output are inverted relative to original transmitted signal in Receive Mode.

The transceiver is available in two variants - TR2I and TR2M

TR2M, in Transmit Mode, 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 Analogue and Digital Data output on the TR2M in Receive Mode. This will be the standard module and exact plug-in replacement for existing industry standard modules.