This sale is for an JRC JST-245 transceiver CMF-144 optional tone board.  While we have sold many of the JST-245 parts, this is the first (and likely last) time that we have had this optional tone board to offer for sale.  Universal Radio sold this board for $109.95 and it was discontinued in 2009.

Installation is relatively easy as it screws into place and then then connects via the wire cables and RF connectors.

The optional CMF-144 was a Monitor Unit (also called a transmit monitor or sidetone/monitor board) for listening to your own transmitted signal. It allowed the operator to monitor (hear) their own transmitted audio or signal quality in real time through the receiver’s speaker or headphones.

This is useful for:

• Checking audio quality, distortion, or compression settings during transmission (especially helpful with SSB or AM).
• Verifying proper operation of the microphone, speech processor, or other transmit audio circuits.
• General self-monitoring in modes where sidetone or transmit feedback isn’t otherwise provided (or to supplement it).

In many high-end transceivers of that era, a dedicated monitor circuit/board like this provided a clean, attenuated sample of the transmitted RF or audio without relying solely on the main receiver (which might be muted or desensitized during TX).

Context in the JST-245

• It was an optional plug-in module (separate from the CCL-267 DTMF/CTCSS tone board, which handled sub-audible tones and DTMF for FM repeaters).
• The service manual has a dedicated section on the CMF-144 Monitor Unit, including circuit description and adjustment procedures.
• It was listed among official JRC accessories and is relatively rare today (often sought by owners restoring or fully equipping these rigs).

This feature was more common on professional or marine-grade equipment (JRC’s background), where operators valued the ability to confirm transmit signal integrity. If you're working on a JST-245, the monitor function is not essential for basic operation but is a nice-to-have for audio/transmit troubleshooting and optimization.

Please use the Ebay shipping calculator to determine your shipping cost.  This cost includes proper packing materials for safe delivery and insurance cost against damage or loss.

Those buyers living outside the USA are also welcome to purchase from us.  We have shipped to 112 countries during the past 26 years on Ebay and we are happy to ship virtually anywhere in the world as served by Ebay's Global Shipping Program.  You may use the shipping calculator to determine your shipping cost.

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