Radiometrix Ltd.,

TX1H high power transmitter data sheet

Page 5

Applications information

Power supply requirements

The TX1H has a built-in regulator which delivers a constant 3.5V to the transmitter circuitry when the

external supply voltage is 3.5V or greater. This ensures constant performance up to the maximum

permitted rail, and removes the need for external supply decoupling except in cases where the supply

TX modulation requirements

The module is factory-set to produce the specified FM deviation with a TXD input to pin 14 of 3V

amplitude, i.e. 0V “low”, 3V “high

If the data input level is greater than 3V, a resistor must be added in series with the TXD input to limit

the modulating input voltage to a maximum of 3V on pin 7. TXD input resistance is 100k

Ω to ground,

giving typical required resistor values as follows:

Vcc

Series resistor

≤3V

3.3V

5V

9V

-

10 k

Ω

68k

Ω

220k

Ω

Expected range

Predicting the range obtainable in any given situation is notoriously difficult since there are many

factors involved. The main ones to consider are as follows:

•

Type and location of antennas in use

•

Type of terrain and degree of obstruction of the link path

•

Sources of interference affecting the receiver

•

“Dead” spots caused by signal reflections from nearby conductive objects

•

Data rate and degree of filtering employed

The following are typical examples – but range tests should always be performed before assuming that

a particular range can be achieved in a given situation:

Data rate

Tx antenna

Rx antenna

Environment

Range

1.2kbps

half-wave

half-wave

rural/open

10-15km

10kbps

half-wave

half-wave

rural/open

3-4km

10kbps

helical

half-wave

urban/obstructed

500m-1km

10kbps

helical

helical

in-building

100-200m

Note: The figure for 1.2kbps assumes that the receiver bandwidth has been suitably reduced by

utilising an outboard sallen-key active audio filter and data slicer or similar arrangement.

The TX1H’s TXD 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 14) be DC-biased to 1.2V approx.

necessary by predistortion of the analogue waveform.

Although the modulation bandwidth of the TX1H extends down to DC 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 receiver’s audio output.