### MOD 3: Local Oscillator Modification for 144MHz IF

Replace the crystal and adjust local oscillator frequency by turing the trimmer.

#### IF and crystal frequency

The original local oscillator frequency is about 2280MHz. Its IF frequency is 120MHz for receiving 2400MHz signal.
The relation between IF and crystal frequency is following.
(Output Frequency) = ((Crystal Frequency) x 256) + (IF)

Crystal Frequency for 144MHz IF is
  (2400MHz - 144MHz) / 256 = 8.8125MHz

Replace the crystal with 8.8125MHz.

* I used a following characteristics crystal.
  Load Capacitance: 20pF
  Frequency Stability: 30ppm

photo 7: replace the X'tal

#### Local Oscillator Turning

After replace the X'tal, adjust local oscillator frequency by turning the trimmer(photo 7, blue arrow). Frequency counter helps this adjustment.

Receiving known frequency signal is also good way. I will show you a simple SG method. Fig 1 shows a simple signal generater(SG). This SG creates 48 times input frequency. Input 50MHz signal goes to 2400MHz.
  - Setup the converter and SG.
  - Put a short wire to the converter's N-type connecter as an antenna. Close to the SG(diode and resister) to the antenna.
  - Set the 50MHz TX frequency and expected RX frequency. (ex. TX = 50.01MHz then SG creates 2400.48MHz. Set RX = 144.48MHz)
  - Transmit 50MHz TX. Don't input much power. Less than 1w is better.
  - Search RX signal and adjust to expected frequency by turning trimmer.
    fig 1: simple Signal Generater
    (by JA7BLS: CQ ham radio Magazine; Nov, 1990)

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