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Brandon Muteboard
For Two-Way Radio Applications

Model Brandon Muteboard

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

  The Brandon Muteboard™ is a professional, yet affordable, add on receive audio CTCSS filter, de-emphasis network, and audio gate on a small circuit board.  

This board can be added to any radio or repeater that has a suitable discriminator audio connection.

It is built with through-hole components to allow assembly, repair or modification by the common technician.

  It is used to create the proper type of audio to feed a (ACC) repeater controller from a discriminator or detector source from the repeater or link radio receiver. 

    Pricing:
  • Unassembled Kit - $30.00 each.
  • Assembled and Tested - $60.00 each.

    • Kit comes with all necessary components, PC board and DB25 female connector.
    Assembled & Tested comes with all parts and DB25 installed and the board tested for proper operation.


    Shipping and handling is calculated at checkout for US and International orders.
    First-Class shipping available to most locations worldwide, calculated at checkout.
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    Actual Size Brandon Mutebpoard render.
    (Click image to enlarge)

    Description - why do we need this board?
    Some repeater controllers require audio that has been filtered to remove CTCSS (PL®) tones, de-emphasize and squelch gate the receive audio before application to the repeater controller. This board accomplishes all of that.

    Not all repeater controllers can handle raw discriminator audio. The ACC line of repeater controllers is one such brand that doesn't. This board fixes all of that. The amout of audio that's fed into the board comes out of the board. In other words, it has a 1:1 level ratio - no gain - no loss.

    Operation:
    The board is active and requires a source of 12VDC at low current. Receive audio is passed through a 5-pole CTCSS reject filter, then actively de-emphasized and squelch gated. The circuitry that provides the CTCSS rejection is a copy of our PLF-15 filter. The de-emphasis curve has unity gain at 1000 Hz and perfectly follows the 6dB/octave slope required by the FM two-way radio industry. The circuitry that mutes the audio is designed to gate the audio without a click or thump. This is done by allowing the mute switch to operate at the 1/2 bias point of the op-amp buffer. The receivers COS line is used to actuate the muting function. A peak detector is used to monitor the audio level. If the audio level exceeds the board's dynamic range - the Red LED will illuminate. Correct (normal) operation requires the Red "CLIP" LED to remain off most of the time. If you see the LED flash occasionally during no signal that's okay - but the LED should never flash or otherwise be lit with a valid signal that has opened the squelch and turned on the Yellow LED.

    About the audio inputs and outputs.
    There is one audio input that is sourced from the receivers discriminator or detector. There is one audio output that has been PL filtered, de-emphasized and squelch gated.

    About the COS logic input.
    There is one logic level input (DB25 Pin-17) to control the muting / unmuting of the audio. The logic line requires an active low. A suitable logic would deliver 0 volts unsquelched and 3 or more volts squelched. This input can be fed from a SC-50(DW) or SC-75(DW) pin 17 - its active low COS output. Any logic that completely turns the Yellow LED off (and on) is acceptable. If using an "open collector" NPN transistor source - an external pull-up resistor is required to provide the bias necessary to switch the logic line.

    Status LEDs.
    There are three status LEDs for visual indication of DC power, unmuting, and clipping. They are Green, Yellow and Red - respectively.

    Features:
    For the most part - the connector pinout is the same as a SC-50 or SC-75.
    Recommended Power Source: +12VDC (+10 to +16 VDC acceptable), must be constant, not switched.   Maximum is 16 VDC.
    3 - LED's for indicating status.
    Low current draw, about 50 mA (Measured at 13.8 VDC input)
    RED CLIP LED indicates when clipping of the audio is occuring.
    Simple to hook up and set up. Requires a few hundred mV RMS of "raw" audio, but can be as much as 8V P-P as long as the board is powered with 12V
    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).
    Comes with DIP IC's, machine sockets, thru-hole resistors and capacitors, and is okay for the first time builder.
    Kits are supplied with all parts ready to solder onto the board.

    Product Documentation   Schematic, parts list, construction, installation and set-up instructions.

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    Shipping amount is calculated at checkout to most locations Worldwide.


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    Email Kevin Custer for ordering information, ordering by check, or support of this exciting product.
     

    Product of Masters Communications, all rights reserved.
    Specifications may change without notice.
    Images are property of Kevin Custer - W3KKC
    Board layout by W3KKC
    HTML September 14, 2023, W3KKC All Rights Reserved!