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Zodiac Seacom 80



Seacom 80

It's not too difficult to make the Zodiac Seacom 80 marine VHF suited for the reception of AIS by adding a discriminator output.

Zodiac Seacom 80

The receiver IC is an MC3357. This IC can be reached easily. The unfiltered audio can be found on pin 9, and also on TP5 next to the IC.

Location of the MC3357
Discriminator Output
Pin 9 and TP5 contain the raw audio
The discriminator output

Follow the next steps to make a discriminator output:

  • Connect a 10 k resistor to TP5
  • Connect another 10 k resitor between the first 10 k resistor and the metal shield (ground). The MC3357's signal level is quite high. The two resistors provide 50% attenuation, so your PC's microphone or line input is not overloaded
  • Connect the positive lead of a 10 uF, 25V electrolytic capacitor 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 the metal shield nearby
  • Lead the shielded wire outside the device and connect a female cinch socket
Overview
Result
Overview of the modification
The 'pigtail'

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 antenna connector, the shielded wire can be led outside and terminated with a female cinch plug.

Obviously, 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.



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