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Kelvin Hughes Husun 70

Husun 70

It's not too difficult to make the Kelvin Hughes Husun 70 marine VHF suited for the recepton of AIS by adding a discriminator output.

Kelvin Hughes Husun 70

The receiver IC, a BA4112, is located on the main circuit board. To make the IC more easily accessible, the top microprocessor board can be expanded. The baseband audio can be found on pin 9 of the receiver IC.

Location of the BA4112
Discriminator Output
Pin 9 of the BA4112 contains the unfiltered audio
The discriminator output

Follow the next steps to make the discriminator output:

  • Connect a 10 k resistor to pin 9 of the BA4112
  • Connect the positive lead of a 10 uF, 25V electrolytic capacitor to the other lead of 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 nearby
  • Connect the other side of the shielded wire to a female cinch socket
  • Connect a 1 k resistor between the cinch socket contacts. The signal level from the BA4112 is quite high. In combination with the 10 k resistor, an attenuation of 20 dB is created, which prevents your PC's microphone input from overloading.
Removing the front

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 power leads, 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.

The 'pigtail'

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