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7DB mod for CTCSS encode following mute on NHRC-3.1

17 November, 2015 - Reading time: 3 minutes

Today we demonstrate how to mod a C1000 CTCSS encoder to follow the receiver mute on a NHRC-3.1 controlled repeater with noise and CTCSS mute options.

  1. Break the track between pins 13 and 14 on the FX315.
  2. Install a PNP transistor between pins 13 and 14.  I used a BC327 from a KL main board wreck.
  3. Connect a 10k resistor to the base of the transistor, and a fly lead to the other end of the resistor.
  4. Install a 1 pin header socket to the other end of the wire, and plug it onto the left pin of the init jumper on the NHRC-3.1
  5. Jobs done.


The idea is that the controller provides the mute signal to the gate on the controller based on a decision made on the presence of carrier and or CTCSS, this signal is used to switch the encoder.  In the past I have simply taken the logic from the receiver, but this is incorrect, as when CTCSS decode is enabled, and noise opens the carrier mute, the tone encoder runs during tail time causing link receivers to think there is still activity on the channel.  This is undesirable.  So the tone encode follows controller mute gating correctly regardless of the muting options selected on the controller.

Some pictures to make it clear.