Custom Products from Masters Communications

Overview:
This board will provide quality logic signals for driving a repeater controller or other radio interface device like URI, RIM, or FOB.   It requires 1V P-P - AC coupled discriminator audio and a source of DC power.   The logic signals can be used together to create a single logically AND'ed output.   This is nice for supplying logic to a controller or other device which only has one logic input, and you want the ability to use both COS and CTCSS in a "AND Squelch" configuration.   It uses discrete circuitry that works exactly like the Motorola MICOR MC6709 or M7716 squelch chip.

If you purchased our kit, refer to the parts list and make sure you have all of the components you need to build the kit.
Click here for the SC-75 Parts List.
Click here for the SC-75DW Parts List.

Construction/Assembly:
If you need assistance with the assembly, Click here for assembly instructions and construction notes - with large photos.

Installation:
This device is intended to be installed inside a radio or project box for protection.   Refer to the schematic for the pinout of the DB25F where all of the logic signals, power connections, and discriminator audio input is listed.   Pin 16 on the DB25 can be used to supply discriminator audio to your controller or other audio interface.
Click here for DB25 and other board connection assignments.

Setting the CTCSS tone frequency:
Click here for DIP switch settings.
1 = ON
0 = OFF
In the photo at the top of the page, the SC-75 is set to 123.0 Hz.

Recommended powering requirements:
The board requires a recommended minimum of 12 VDC to put the regulators into full regulation.  While the board will operate at a lower voltage input, the noise squelch circuitry may become erratic.   The maximum recommended voltage is 16 VDC, however, the voltage regulators will survive up to 24 VDC before damage occurs.  The board has been tested with as low as 11 VDC and the board still seemed to operate normally.

Recommended discriminator audio input level:
We recommend 1.5V peak to peak of noise at the board input.   (Measured with No RF input signal to the receiver).  Too much discriminator audio level makes setting the squelch difficult - even with a 25 turn pot. We don't recommend going lower than 1.0V P-P or you start to starve the CTCSS decoder. While the board will work fine with audio levels between 1.0V and 5.0V P-P, again 1.5V P-P is best. If you have too much audio, a simple resistor in series with the input will create a voltage divider (against the squelch pot) and reduce the input to a more desirable level.  A value in the 1 to 100k range is approximately what should be expected, depending on the audio level that is too high.   Input levels are somewhat dependent on the type of receiver, characteristics of the discriminator, and how much high-frequency energy is present in the recovered audio.  If you have too little audio, a simple audio amplifier may be required to meet the required input level of the board.  Refer to this amplifier project (the first one) if necessary.

CAL LED:
The "CAL" LED can be enabled and disabled by jumper SJ6 across the red 2-pin header. When setting the squelch control on the SC-75, it's okay (actually desirable) if the CAL LED flashes. I know it seems that you're setting it on the hairy edge, but just as long as the "SQ" and "COS" LEDs aren't flashing too, you should be good to go. Of course, if you like a little tighter squelch, just set it so the CAL LED is on solid. If after setting the squelch, the CAL LEDs flicker bothers you, you can remove a jumper (SJ6) to disable this LED.

Explanation of the logic signals and other pins:
Active high and active low outputs for CTCSS and COS logic are available.   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 open collector and are available on the DB25, and from 6 holes on the circuit board.   These outputs can be used for operations that are beyond the original scope of this board.

For "AND" mode, the COS output is the one that's used.   Pull-down resistors are included on the logic high outputs.   Obviously if you are using this board and need active low outputs you should be using the outputs connected to the NPN transistors, but, the on-board pull-down resistors can make circuitry respond correctly when using the active high PNP outputs.

All logic is sourced from +5V and ground.   +5 volts is the logic value expected directly from the collector of a PNP logic transistor that is biased on.   Ground is the logic value expected directly from the collector of a NPN transistor that is biased on.

The normal outputs that connect to the DB25 should satisfy most of the devices you'll connect to this board.   For those instances where they don't, you can use the outputs labeled A - F.   These outputs are available from "holes" on the circuit board, marked A - F on the silkscreen. Outputs B and F share the same hole.   These outputs connect directly to the collectors of the logic transistors before any current limiting resistors.   There are three extra pins on the DB25 pins 7, 12, and 25 which can be jumped to any of these additional outputs.   Caution should be given to the use of any of these additional outputs as they are unprotected, and misuse will cause switching transistor failure.   While the PNP transistors have the over-current protection of the 5 volt regulator, there is no protection for the NPN to ground.   Be certain that your connection to these outputs don't exceed the capabilities of the board or switching transistor.

The SJ1/SJ2 header allows pin 1 on the DB25 to be an input or output.   If the user desires the COS and CTCSS outputs to operate independently, they would place a jumper in the SJ1 position.   This allows pin 1 on the DB25 to be an active low CTCSS logic output.

If this header is jumped with SJ2, the logic signals are used together in AND Squelch mode.   If SJ2 is in place, grounding pin 1 of the DB25 disables the requirement for CTCSS.   In other words it disables the CTCSS requirement and the logic at the COS outputs are only controlled by the status of the noise squelch - CTCSS is ignored or "disabled".

The SJ3/SJ4 header allows the PTL function to be selected remotely.   Normally, this jumper will be in the SJ3 position - which disables the remote select option.   If you want to use this option, place the jumper in the SJ4 position and selectively ground either the "PTL" hole or pin 14 on the DB25.   Refer to the manual download below to see what this function is, and what it does.

SJ5 takes discriminator audio and puts it into the RX audio filter input so you don't have to wire two pins together or otherwise route discriminator audio into the unit twice. This is beneficial in the installation of the SC-75 in a Yaesu System Fusion repeater, or any other installation where you desire to have CTCSS reject filtered receive audio. SJ5 is simply a shorting bar that parallels pins 2 and 3 on the DB25.

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

Third Party Compatible Projects:
MABEL is an interface and software that allows analog control of the Yaesu DR-1X repeater and access to the AllStar VOIP network with the Raspberry Pi3 and AllStar Asterisk. (Offsite Link)

MABEL Specific Information for the Yaesu System Fusion DR-1X and / or DR-2X:
With great assistance from Steve N8AR we have ignition! He helped me through zoom. Here are the specifics:

1 - When using the SC-50(DW) do NOT ground X3-4 on the MABEL board, only ground this if you are NOTusing an SC-50.

2 - There a difference in wiring between the DR-1X and DR-2X.
For the DR-1X - on the 15 pin accessory connector, pins 10 & 11 are jumped together, and pin 12 goes to X3-3 on the MABEL Board.

For the DR-2X - pins 10 & 12 are jumped together, and pin 11 goes to X3-3 on the MABEL Board.

You can add this to your directions, it’s working like a charm!

73 Dave VA3NSC

Information on the FX465.
Click here to download a manual for the FX465-D5

Email Kevin Custer for support of this exciting product.
 
 

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