APF MP1000

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Chip Info


Schematics


Adjustments

From the APF Programming and Technical Assistance Manual

A. R.F. Output

  1. The R.F. Output Frequency is set by L1 and C5. Ll is an air core coil and will allow approximately a +-6 MHZ adjustment from the factory set frequency of 61.25 MHZ (with C5 = 39 pF). By changing C5 to 27pF, the resonant frequency becomes approximately 67 MHz (U.S. Channel 4)
  2. The R.F. output goes through a sideband filter whose bandwidth is approximately 6MHZ. It can be adjusted by tuning L2 to give a peak output of the upper sideband.

B. Tuning Procedure for R.F. output (Channel 3)

  1. Connect R.F. output cable of MP1000 to spectrum analyzer or calibrated field strength meter.
  2. Switch MPl000 power on.
  3. Adjust coil L1 to read 61.25 MHZ (TV Channel 3).
  4. Adjust coil L2 to get maximum output signal strength then adjust the tuning point of L2 to 1 MHZ higher than TV Channel 3 signal (ie, 62.25 MHZ) or tuning of L2 to reduce maximum output signal level by about 1 db. This also gives a tuning point close to 62.25 MHz.

CRYSTAL OSCILLATOR

A. VC1 is a variable capacitor to allow adjustment of the xtal oscillator frequency. This clock should be adjusted to give exactly 3.579545 MHz. B. VR1 allows an adjustment of the duty cycle. It should be adjusted to give a duty cycle between 45 and 55%.

SOUND OSCILLATOR

The sound subcarrier frequency can be adjusted by tuning L3. It should be adjusted to give an unmodulated frequency of 4.500 MHZ.