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The next generation CAR UNIT for the Kenwood TS850 transceiver

I have developed this board as a aftermarked replacement for the Kenwood CAR UNIT (X50-3140-00) with four YM6631 and/or YM66312 DDS chips, which is no longer available as original spare part. Furthermore, there are no longer any of these chips available to replace the old ones:

Kenwood CAR UNIT (X50-3140-00)20191202_200635-1024

The original Kenwood CAR UNIT board (X50-3140-00), installed in the TS850

The CAR UNIT do many different things in the TS850: from generating 4 different RF signals used as LO signals in the mixers – to even generating the side tone when sending CW or CTCSS sub tones in FM split mode.

To replace the original CAR UNIT, the new board was developed based on a high performance FPGA chip (Field Programmable Gate Array), which include the function of all 4 ASIC’s YM6631/YM66312 and some peripheral circuits in only one chip !!




The NG CAR UNIT is available from RF-SYSTEM‘s webshop.


First, all internal functions of the original YM6631 chip was completely reproduced as a VHDL model, including a DDS (Direct Digital Synthesis) and implemented in the FPGA with some improvements.

Logic_blocksDue the high performance of the FPGA the functions of the peripheral circuits (mixers, ceramic filters etc.) could be minimized to achieve a higher design flexibility of this board. Furthermore, a high spectral purity of generated RF signals and matched output levels are the results of an accurate signal routing, PCB design and analog circuits:

DLO1_rbw100Hz_span200kHzDLO3_rbw100Hz_span200kHzCAR_rbw100Hz_span200kHzThe accurate design of all functions implemented in the FPGA for the communication with the TS850’s digital unit are high speed optimized and allow a glitch-free, smooth tuning operation.

The prototype of NG CAR UNIT board for the KENWOOD TS850:


  All screw mounting holes are in the same location and all connector labels have the same description on the printed circuit board as on the original unit, which permit a easy “plug and play” replacement of a defectiv CAR UNIT. Furthermore there are no alignments necessary on the transceiver after the replacement of this board.

The development setup for the NG CAR UNIT board mounted in a KENWOOD TS850:



The NG CAR UNIT is available from RF-SYSTEM‘s webshop.