RF83 datasheet(12/22 Pages) ETC2

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

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13.1.1.3. Crystal or Ceramic Resonator Selection

If operating in fixed-mode, a crystal is recommended. In sweep-mode either a crystal or ceramic resonator

may be used. When a crystal of ceramic resonator is used the minimum voltage is 300mVPP. If using

an externally applied signal it should be AC-coupled and limited to theoperating range of 0.1VPP to

1.5VPP.

13.1.1.4. Selecting Reference Oscillator Frequency fT (Fixed Mode)

As with any superheterodyne receiver, the mixing between the internal LO (local oscillator) frequency fLO

and the incoming transmit frequency fTX ideally must equal the IF center frequency. Equation 1 may be used

to compute the appropriate fLO for a given fTX:

(1) fLO =fTX ±(0.86

fTX

)

315

Frequencies fTX and fLO are in MHz. Note that two values of fLO exist for any given fTX,

distinguished as “high-side mixing” and “low-side mixing.” High-side mixing results in an image

frequency above the frequency of interest and low-side mixing results in a frequency below.

After choosing one of the two acceptable values of fLO, use Equation 2 to compute the reference

oscillator frequency fT:

(2) fT =

FLO

64.5

Frequency fT is in MHz. Connect a crystal of frequency fT to REFOSC on the RF83.

Four-decimal-place accuracy on the frequency is generally adequate. The following table

identifies fT for some common transmit frequencies when the RF83 is operated in fixed

mode.

Transmit Frequency (fTX)

Reference Oscillator Frequency (fT)

315MHz

4.8970 MHz

390 MHz

6.0630 MHz

418 MHz

6.4983 MHz

433.92 MHz

6.7458 MHz

Table 2. Fixed Mode Recommended Reference Oscillator Values For Typical Transmit

Frequencies (high-side mixing)

13.1.1.5. Selecting REFOSC Frequency fT (Sweep Mode)

Selection of the reference oscillator frequency fT in sweep mode is much simpler than in fixed

mode due to the LO sweeping process. Also, accuracy requirements of the frequency reference

component are significantly relaxed.

In sweep mode, fT is given by Equation 3:

(3) fT =

FLO

64.25

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