Making the NHRC-4/M2 controller provide
CTCSS (PL) only during COS activity.

- TS-64 boards only -
By Kevin Custer W3KKC

Concept:  The NHRC-4/M2 controller allows the connection of the newer Com-Spec TS-64 CTCSS encoder/decoder.  From the factory, the controller can be configured to provide reverse burst if the logic is provided from the controller to the TS-64, but what if you only want the PL tone on the repeater transmitter when the receiver is active (PL during COS activity only)?

The solution is simple.  Since the logic input already exists (Transmit PTT Input) on the TS-64 to allow the keying of the CTCSS tone when this pin is grounded, all we need to do is provide a keyed ground signal to it when the COS (CAS) is active.

Explanation:  This modification eliminates the ability of the TS-64 from keying the transmitter through the controller as originally intended by NHRC.  The two pin PTT interface jack, JP4, is reconfigured to provide a switched ground to JP4, pin 2, from the COS transistor on the controller.  This allows the TS-64 to operate as a keyed CTCSS encoder.  Reverse Burst is generated when the COS disappears (user unkeys) and since the repeater controller has hang time, no keying is needed from the TS-64 to the transmitter.  One of the jumpers added below restores the PTT line as if jumper connector JP4 was never modified and the jumper was installed.

CAUTION:  Use extreme care when cutting the trace on the component side of the controller.  Cut only the wide trace leading to pin 2 of JP-4, and nothing else.
Pin 2 of JP4 is the pin closest to Q5.

Detail:  Jack JP4 on the controller is rewired to supply a keyed ground to the orange lead (pin 8) on the TS-64.  Pin 2 of JP-4 is rewired to provide a keyed ground when the controller has a valid COS.

  1. Cut the circuit trace as marked in the upper image below.
  2. Add the two jumpers as shown in the second image.
  3. Connect the orange lead (pin 8) on the TS-64 to JP4 pin 2.
  4. Use at least 200 mS hang time on the repeater controller.

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Article text and layout © Copyright 2004 and date of last update by by Kevin K. Custer W3KKC and

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.