RX2G Просмотр технического описания (PDF) - Radiometrix Ltd

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RX2G

UHF FM Data Transmitter and Receiver Modules

Radiometrix Ltd 

Power supply requirement

The standard TX2A module incorporates a built-in regulator which delivers a constant 2.8V to the module

circuitry when the external supply voltage is 2.85V or greater, with 40dB or more of supply ripple rejection. This

ensures constant performance up to the maximum permitted supply rail and removes the need for external

supply decoupling except in cases where the supply rail is extremely poor (ripple/noise content >0.1Vp-p).

Note, however, that for supply voltages lower than 2.85V the regulator is effectively inoperative and supply

ripple rejection is considerably reduced. Under these conditions the ripple/noise on the supply rail should be

below 10mVp-p to avoid problems. If the quality of the supply is in doubt, it is recommended that a 10F low-

ESR tantalum or similar capacitor be added between the module supply pin (Vcc) and ground, together with a

10 series feed resistor between the Vcc pin and the supply rail.

The Enable pin allows the module to be turned on or off under logic control with a constant DC supply to the

Vcc pin. The module current in power-down mode is less than 1A.

NOTE: If this facility is used, the logic control signal must have a slew rate of 40mV/ms or more. Slew rates less

than this value may cause erratic operation of the on-board regulator and therefore the module itself.

The TX2A incorporates a low voltage shutoff circuit, which prevents any possibility of erratic operation by

disabling the RF output if the supply voltage drops below 2.2V (±5%). This feature is self-resetting, i.e. restoring

the supply to greater than 2.2V will immediately restore full RF output from the module.

The standard RX2G requires a regulated 5V supply with ripple content <100mVpk-pk.

However, a built-in regulator version is also available. The regulator version can be operated from 5V

(minimum) up to 16V (maximum permitted) supply rail and removes the need for external supply decoupling

except in cases where the supply rail is extremely poor (ripple/noise content >0.1Vp-p).

TX2A modulation requirements

The module will produce the specified FM deviation with a TXD input to pin 7 of 2.5V amplitude, i.e. 0V "low",

2.5V "high". Reducing the amplitude of the data input from this value (usually as a result of reducing the supply

voltage) reduces the transmitted FM deviation to typically ±25kHz at the lower extreme of 2.2V. The receiver

will cope with this quite happily and no significant degradation of link performance should be observed as a

result.

Where standard 2-level digital data is employed with a logic "low" level of 0V ±0.2V, the logic "high" level

applied to TXD may be any value between +2.5V and +3V for correct operation. However, if using multi-level or

analogue signalling the maximum positive excursion of the modulation applied to TXD must not exceed +2.5V

or waveform distortion will result. If the input waveform exceeds this level a resistive potential divider should be

used at the TXD input to reduce the waveform amplitude accordingly. This input is high impedance (>100k)

and can usually be ignored when calculating required resistor values.

Received Signal Strength Indicator (RSSI)

The RX2G module incorporates a wide range RSSI which measures the strength of an incoming signal over a

range of approximately 60dB. This allows assessment of link quality and available margin and is useful when

performing range tests.

Please note that the actual RSSI voltage at any given RF input level varies somewhat between units. The RSSI

facility is intended as a relative indicator only - it is not designed to be, or suitable as, an accurate and

repeatable measure of absolute signal level or transmitter-receiver distance.

The output on pin 5 of the module has a standing DC bias in the region of 0.5V with no signal, rising to around

1V at maximum indication. The RSSI output source impedance is high (~100k) and external loading should

therefore be kept to a minimum.

To ensure a fast response the RSSI has limited internal decoupling of 1nF to ground. This may result in a small

amount of ripple on the DC output at pin 5 of the module. If this is a problem further decoupling may be added

at the expense of response speed, in the form of a capacitor from pin 5 to ground. For example, adding 10nF

here will increase RSSI response time from 100µs to around 1ms. The value of this capacitor may be increased

without limit.

Radiometrix Ltd, TX2A/RX2G Data Sheet

page 6

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