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Sailtron R/T 80

Sailtron R/T 80

It's not too difficult to make the almost antique marine VHF Sailtron RT80 and the identical Sealine MC5500 suited for the recepton of AIS by adding a discriminator output.

Sailtron RT80

The VHF transceiver uses a conventional discriminator, consisting of a ceramic resonator and two diodes. Usually, the performance of this type of discriminator is less than that of a receiver with a more modern receiver IC. In spite of that, for the R/T 80, the results were quite acceptable.

The unfiltered audio can be found on the cathode of diode CR162. This diode can be found right next to the ceramic resonator.

Location of CR162
Discriminator Output
The cathode of CR162 contains the unfiltered audio
The connection to CR162

Follow the next steps to make the discriminator output:

  • Connect a 10 k resistor to diode CR162
  • Connect a 2.2 nF capacitor to the resistor's other lead. The other lead of the capacitor is soldered to the metal shield of the IF coil.
  • Connect the positive lead of a 10 uF, 25V electrolytic capacitor to the junction of the resistor and 2.2 nF capacitor
  • 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
Pig tail

Because the case is isolated from the transceiver's internal ground, I have not put a chassis terminal in the case, but used a 'pig tail' in stead. If a small hole is drilled next to the existing loudspeaker socket, the shielded wire can be led outside and terminated with a female cinch plug.

Of course, it is also possible to use a longer cord and use a 3.5 mm plug to connect the signal directly with your PC's line or microphone input.

The discriminator output: a 'pig tail' with a female cinch plug

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