PL and the NHRC-4 Controller
By Kevin Custer W3KKC

The NHRC-4 repeater controller is designed to work in conjunction with the Com-Spec TS-32, or TS-64 CTCSS (PL) encoder / decoder board.  The Digital Logic / Fan Switch Output can be configured to allow the repeater to be put into PL or Carrier Squelch Access.  This is done by disabling the Com-Spec unit through the Hang-Up lead.  As intended by NHRC, the Com-Spec decoder supplies the controllers' main receiver CTCSS input with a active-low or negative logic signal.  In other words the controller needs to be supplied with a ground upon receiving a PL tone.  This is uncommon of original equipment decoders like the MICOR PL deck as they provide a voltage when receiving the proper tone.  If you would like to use your original equipment decoder and want the ability to put the repeater in and out of PL....slight modification of the controller is necessary.  This modification is very simple and functionality is the same as if a Com-Spec unit were used.

Allow the connection of a MICOR PL decoder (or similar OEM decoder) to a NHRC-4 controller.
NOTE:  This modification is NOT necessary when connecting a Com-Spec unit to the controller.  Provisions are in the manual for connecting a Com-Spec unit to the controller and allowing it to be turned OFF/ON.

Advantages-  After modification the controller will accept a positive going (active-high) PL signal and enabling and disabling will be handled totally on the controller board.  No enable / disable leads will need to be connected to the PL decoder.

Modification-  The controller needs modified to allow a decoder that supplies a voltage upon receiving a signal to be connected and have the stated advantages as above.

(1) Cut out R3, a 10K pullup bias resistor that supplies the main ctcss logic input voltage.  This voltage is not necessary since your decoder will be supplying the controller with logic voltage.  Either remove the resistor or snip the loop at the top where the lead is bent over and insure separation of the severed conductors.

(2) Place a thin insulated jumper wire from the Digital Output (J1 pin 6) to the collector of Q3.  This enables carrier squelch by shorting Q3 to ground.  I connect the jumper to the trace leading to the J1 jack by scraping off the protective enamel.  The other end connects to the Q3 collector lead or pad.

(3) VERY IMPORTANT!  Supply the controller with logic voltage from your decoder THROUGH a 10 K resistor or destruction of Q3 will result.  There is no current limiting bias resistor connected to the base of Q3 and therefore one must be added.  The transistors base lead can be cut and the resistor added to the board or simply add a resistor in series with the J3 pin 5 connection.  This can even be done in the radio.

Operation-  The controller can be set to Carrier Squelch or PL by enabling or disabling the Digital Output with the pppp02xx command, where pppp is the custom passcode, 02 is the Digital Logic address and xx is the function of either OFF or ON.  Do Not set this address to "pulsed" by entering 02 in the xx position.

This operation can be looked at as putting the repeater in and out of Carrier Squelch operation.... In other words enabling or disabling carrier squelch.  Disabling carrier squelch enables PL operation.

Lets say your passcode is "1234"....
To put the repeater in Carrier Squelch, key-up and enter 12340201
To put the repeater in PL, key-up and enter 12340200

Since the logic for the Digital Output is held in non volatile memory the controller will stay in which ever state last selected even after power failure. So, if the repeater was in Carrier Access and the power failed... the repeater would be enabled in Carrier Access when power is restored.

This controller handles the logic for PL as "AND Squelch".  Go here to understand what this is.

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This page originally posted on 30-Jul-2000

Article text and layout © Copyright 30-Jul-2000 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.