Analog Noise Squelch
and CTCSS decoder.
For Two-Way Radio Applications
Model SC-50 Click here for schematic, parts list, construction, installation and set-up instructions.
Ordering instructions on bottom of page.
This board can be added to any radio or repeater that has a suitable discriminator connection.
It is built with mostly through-hole components to allow repair or modification by the common technician.
It is used to create a quality noise squelch and CTCSS logic to be interfaced with a standard repeater controller or radio interface with AllStar, IRLP, or similar application.
This board uses the Motorola MICOR squelch chip for noise squelch detection.
Kit - you supply your own MICOR squelch chip - $50.00 each.
Kit with MICOR squelch chip - $75.00 each.
Assembled and tested without the MICOR squelch chip - $75.00 each.
Assembled and tested with MICOR squelch chip - $100.00 each.
US shipping and handling $7.50 in small quantity.
PayPal accepted - order below.
NOTICE: My stock of new MICOR squelch
chips has been depleted, HOWEVER, used - tested - and guaranteed chips are available.
I have a huge stock of these parts to fulfill orders way into the future.
Actual Size SC-50 photo.
(Click image to enlarge)
The SC-50 is a MICOR noise squelch, and a CML CTCSS decoder on a single printed circuit board. The board uses a genuine MICOR M6709 (M7716), as I have yet to find anything superior. A MX-465 (FX-465) CTCSS chip is used for "PL" 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/FX-465 is the only surface mount component. There is a socket provided for the MICOR squelch chip. Sure, the MICOR squelch chip is no longer available as a new part from Motorola, however, there are thousands of MICOR radios which are surplus. Many of you can source this part for free. As an option, it is available from me for $25.00 as a used/tested/guaranteed part.
There are three differently colored LEDs for status. One is blue and indicates a valid carrier squelch detection. The second is red and indicates a valid CTCSS (PL) tone detection. The third is green for COS, which indicates both COS and PL are valid in "AND" mode. The tone frequency is set by DIP switches. All of the functionality of the FX-465 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 PL 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 PL logic signals. Some repeater hardware may not include a conventional squelch control or may require reprogramming just to change the PL 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 PL 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 or Arcom RC-210.
|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 MICOR chip, and 5V for the FX465 and logic.|
|Squelch control is simple 3/4 turn potentiometer.|
|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.|
|Option to disable fast/short squelch operation. This is done by adding a 22k resistor in the "RD" position. This part is NOT supplied.|
|Option to shorten the long/slow squelch hang time. This is done by adding a resistor
in the "RX" position.
This value can be whatever the user chooses as it will work in conjunction with the original 180k. This part is NOT supplied.
|Small size - can fit inside many radios.|
|My stock of new (NOS) MICOR squelch chips has been depleted. Used, tested, and guaranteed chips are available with the same 90 day Limited Warranty.|
|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).|
|Kit comes with thru-hole resistors and capacitors, but isn't recommended for the first time
builder due to surface mount IC.
The kit can be supplied with the surface mount 24 pin IC already soldered onto the board. Just ask, or select below - $5.00 charge for this service.
Click here for schematic, parts list, construction, installation and set-up instructions.
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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 November 15, 2014, W3KKC All Rights Reserved!