1. 1. Internal AF Input gain is factory set for 1Vpk-pk to produce 3kHz peak deviation and minimum distortion. Analogue gain may be set for an input level of 50mV - 2V pk-pk. This cannot be done without appropriate test equipment. Contact factory for details

3. Carrier detect on RX2M mutes the AF and DATA outputs when RF input signal is <-123dBm. This can be factory disabled if required.

4. There are no pullups on the open collector outputs. External pull-up resistor should be used

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

TX2M and RX2M serial interface commands

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

Transmit (pin 3 on DB9) and Signal Ground (pin 5 on DB9) should be connected to PGM and 0V pin.

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)

Note: Audio and voice signals should be avoided in the band 433.050MHz - 434.790MHzPower density limited to -13dBm/10 kHz for wideband channels with a bandwidth greater than 250 kHz

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.

Operating principle of internal modem

This device is a simplex link handling a 1200 baud asynchronous datastream (1 start, 8data, 1stop). Buffering in the transmit end handles TX startup timing requirements, while the presence of sync codes in the transmitted bursts prevents the receiver from outputting garbage in the presence of noise. No error correction or retransmission of lost packets is supported. To operate with proper +/-12V RS232 levels an external buffer (such as a MAX232) will be needed

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

Both transmit and receive modems implement a 32 byte software FIFO. At the transmit end this is used to allow for the TX2M transmitter start up time (about 32ms), while on receive it buffers arriving packets to the constant output data rate. All timing and data formatting tasks are handled by the software. The user need not worry about keying the transmitter before sending data: the link is entirely transparent.

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

Raw data is not fed to the radios. A coding operation in the transmit software, and decoding in the receiver, isolate the AC coupled, potentially noisy baseband radio environment from the datastream.

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

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.

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