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RF83//RF83C/RF83L/RF83CL ASK/OOK Receiver V2.0

 

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13.1.1. Step 1: Selecting the Operating Mode

13.1.1.1. Fixed-Mode Operation

For applications where the transmit frequency is accurately set (that is, applications where a SAW or crystal-

based transmitter is used) the RF83 may be configured as a standard superheterodyne receiver (fixed mode).

In fixed-mode operation the RF bandwidth is narrower making the receiver less susceptible to interfering

signals. Fixed mode is selected by connecting SWEN to ground.

13.1.1.2. Sweep-Mode Operation

When used in conjunction with low-cost L-C transmitters the RF83 should be configured in sweep-mode. In

sweep-mode, while the topology is still superheterodyne, the LO (local oscillator) is swept over a range of

frequencies at rates greater than the data rate. This technique effectively increases the RF bandwidth of the

RF83, allowing the device to operate in applications where significant transmitter-receiver frequency

misalignment may exist. The transmit frequency may vary up to ±0.5% over initial tolerance, aging, and

temperature. In sweep-mode a band approximately 1.5% around the nominal transmit frequency is captured.

The transmitter may drift up to ±0.5% without the need to retune the receiver and without impacting system

performance.

The swept-LO technique does not affect the IF bandwidth, therefore noise performance is not degraded

relative to fixed mode. The IF bandwidth is 430kHz whether the device is operating in fixed or sweep-mode.

Due to limitations imposed by the LO sweeping process, the upper limit on data rate in sweep mode is

approximately 5.0kbps.

Similar performance is not currently available with crystal-based superheterodyne receivers which can

operate only with SAW- or crystal-based transmitters.

In sweep-mode, a range reduction will occur in installations where there is a strong interferer in the swept

RF band. This is because the process indiscriminately includes all signals within the sweep range. An RF83

may be used in place of a superregenerative receiver in most applications.

13.1.2. Step 2: Selecting the Reference Oscillator

All timing and tuning operations on the RF83/RF83C are derived from the internal Colpitts reference

oscillator. Timing and tuning is controlled through the REFOSC pin in one of three ways:

1) Connect a ceramic resonator

2) Connect a crystal

3) Drive this pin with an external timing signal

The specific reference frequency required is related to the system transmit frequency and to the operating

mode of the receiver as set by the SWEN pin of RF83.