Custom Products from Masters Communications

Description:
The SC-75DW is a MICOR "type" noise squelch, and a CML CTCSS decoder on a single printed circuit board.   The board uses discrete circuitry to emulate the famous Motorola MICOR 6709 [7716] squelch chip.   A MX-465DW CTCSS chip is used for CTCSS detection.   This chip is not duplex - meaning it will not generate (encode) and decode a tone simultaneously.   Since the main purpose of this board is to allow easy connection of detected logic to a repeater controller, AllStar or other radio interface, the CTCSS encode would be done elsewhere in hardware or software.   The MX-465DW and three op-amps are the only surface mount components. All of them are preinstalled on the kit.

There are four differently colored LEDs for status.   One is blue and indicates a valid carrier squelch detection.   The second is red and indicates a valid CTCSS tone detection.   The third is green for COS, which indicates both COS and CTCSS are valid in "AND" mode.   The fourth is yellow and aides in the correct calibration and setting of the squelch control.   The tone frequency is set by DIP switches.   All of the functionality of the MX-465DW is brought out to pins on the connector (DB-25F).   They include the logic line to tell the chip to encode or decode, as well as all of the audio filters and muting that is available for the transmitter and receiver - in case someone wants to utilize them.   There are three 'spare' traces on the circuit board allowing you to have access to three different pins on the DB-25F that you may jumper to anywhere on the board you like.

About the inputs and outputs.
There are only three necessary connections for input; buffered discriminator audio, power, and ground.

The logic outputs for CTCSS and COS are not totem pole, however, both active high and active low are available for both of these signals.   For "AND" mode, the COS outputs are the ones that are used.   Both active high and active low are available for the COS logic output, irregardless if this output is being used in "AND" mode.   The outputs are not selectively inverted, however, all of these open collector outputs are available from 6 holes marked A - F that are included on the circuit board.   These outputs can be used for operations that are beyond the original scope of this board.

There are three spare hole traces that terminate to individual pins on the DB25.   They can be used to wire up things I may not have thought of.

Why do we need this board?
Not all radios have easy access to quality COS and CTCSS logic signals.   Some repeater hardware may not include a conventional squelch control or may require reprogramming just to change the CTCSS tone frequency.   Some radios have inferior noise squelches.   DSP in AllStar applications is good, but nothing beats a MICOR noise squelch.   Plus, this allows you to use hardware COS and CTCSS signaling which side-steps the known issues of the 'yucky blanking code' that sometimes punches holes in the audio stream in app_rpt.   Some platforms (like the BeagleBone Black) are not currently intended for DSP operation, and this board will give the necessary logic signals from just about any radio that has a discriminator audio output.   This board is a nice addition to the Yaesu System Fusion repeater when connecting a repeater controller like the SCOM 7330, the Arcom RC-210, or MABEL.

Features:

	Recommended Power Source: +12 to +16 VDC, must be constant, not switched.   Maximum is 24 VDC.
	Onboard regulation for both sections.   9.6V for the squelch logic, and 5V for the MX465DW and logic.
	Squelch control is 25 turn trim-pot
	CTCSS tone is set by DIP switches.
	Low current draw, about 25 mA standby and 60 mA with all LEDs lit, depending on logic sourced and its input impedance.
	All logic is sourced from 5 VDC.   Pull-up and pull-down resistors are included.
	Small size - can fit inside many radios.
	Add a quality squelch and CTCSS decoder to that radio whose logic signals are hard to get to.
	Great for AllStar - app_rpt or connecting up your favorite repeater controller!
	Simple to hook up and set up. Requires a few hundred mV RMS of audio that is AC coupled.
	90 day Limited Warranty.  Repair available for units out of, or not covered under warranty (my determination).
	Mounts with double-sided foam tape or stand-offs (not included).
	Hookup is made with a mating DB25 male connector (not included).
	Compatible with MABEL MABEL allows analog control of the Yaesu DR-1X repeater and access to the AllStar VOIP network. (Offsite Link)
	Kit comes with thru-hole resistors and capacitors, and 4 pre-installed surface mount ICs.     The kit is supplied with the four surface mount ICs already soldered onto the board.

Click here for schematic, parts list, construction, installation and set-up instructions.

Evaluation Article of the SC-75 by Bob Meister WA1MIK.

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SC-75DW

Unassembled SC-75DW Kit

Assembled & Tested SC-75DW

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Product of Kevin Custer - W3KKC, all rights reserved.
Specifications may change without notice.
Images are property of Kevin Custer - W3KKC
Board layout by Chuck Kelsey - WB2EDV
HTML April 24, 2019, W3KKC All Rights Reserved!