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Skanti TRP 2500

Skanti TRP 2500

The Skanti TRP-2500 is a rather vintage marine VHF radio. It's spacious layout makes it easy to enable AIS reception by adding a discriminator output.

Skanti TRP2500

The receiver IC is an MC3357. The unfiltered audio can be found on pin 9. The output signal has a peak-peak voltage of about 5 V. A voltage divider is used to attenuate the output signal by about 10 times and protect the line- or microphone input of a connected PC.

Discriminator Output
Pin 9 contains the unfiltered audio
The connection to pin 9
With the following steps, the discriminator output is made:
  • Solder a 10 k resistor to pin 9 of the MC3357
  • Solder a 1 k resistor from the other lead of the 10 k resistor to ground
  • Connect a 10 uF, 25 V electrolytic capacitor with its plus-lead to the junction of the two resistors
  • Connect the inner conductor of a piece of shielded wire to the negative lead of the capacitor
  • Connect the braid to ground
  • Lead the shielded wire outside through the holes in the circuit board and the heatsink
  • Mount a 3.5 mm mono audio connector on the shielded wire.
The shielded wire is led outside

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