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Dantronik RT 408D / Dancom RT925

Dantronic RT408D

It's not too difficult to make the Dantronik RT480D and the almost identical Dancom RT925 marine VHF suited for the reception of AIS by adding a discriminator output.

Dantronic RT 480 D

The receiver IC is a TBA120U, which was originally designed for use in TV's. This IC has two audio outputs: pin 8, which is adjustable by the volume potmeter, and pin 12, which carries a signal with a constant level. For AIS, pin 12 is the most suited.

Discriminator Output
Pin 12 carries the unfiltered audio
The connection to pin 12

Follow the next steps to make the discriminator output:

  • Connect a 10 k resistor to pin 12 of the TBA120U
  • Connect the positive lead of a 10 uF, 25V electrolytic capacitor to the resistor
  • Connect the inner conductor of a piece of shielded wire to the negative lead of the capacitor
  • Connect the braid to the metal shield of the nearby coil
  • Connect the other end of the shielded wire to a 3.5 mm chassis socket
Chassis socket

The 3.5 mm socket can be mounted in the back of the VHF set, close to the combined power supply/ handset plug.

The 3.5 mm chassis socket

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