Measure required voltage for deviation +/- 3kHz

By G3RUH

Marco - I do not know how many millivolts are required on your radio to set the deviation to +/- 3 kHz. But here are two simple ways to find out.

Method 1

  1. Monitor UO-14 on a scope connected to G3RUH 9600 baud modem TP4. Measure Pk-Pk voltage. This corresponds to about +/- 2.5 kHz
  2. Set RX to 435.0 MHz, TX to 145.0 MHz. Power level to min. Key up TX. Reduce pot VR1 on modem until signal (third harmonic) at TP4 is the same size as UOSAT was. Measure TXAudio voltage pk-pk at modem output P3-1.
  3. Adjust VR1 until this TXAudio voltage is exactly 3x bigger.
    You now have the TX deviation the same as UOSAT.

Method 2.

By this method you will calibrate the TS790 RX as a deviation meter.

  1. RX = 435.0 MHz, TX=145.0 MHz, Power to min, Modem VR1 to zero.
  2. Scope on Discriminator output. Use 10k/100pf to remove junk if needed.
  3. Key up TX. Scope output should change from noise to flat DC.
  4. Change TX by +/- 1 kHz. Note change in discriminator voltage. This gives RX sensitivity in volts per +/-3 kHz.
  5. Restore TX to 145.000, increase VR1 until /- peaks of signal are same as noted in test 4. Note TXAudio pk-pk voltage at P3-1.
  6. Increase VR1 to give exactly 3x more voltage at P3-1.
  7. You now have TX deviation +/- 3 kHz pk/pk

73 de James G3RUH @ UO14 1991 Sep 19

Click here to read more mods for the TS-790