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The next generation CAR UNIT for the Kenwood TS450S and TS690S transceivers

I have developed this board as a aftermarked replacement for the Kenwood CAR UNIT (X50-3160-00) with two 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 (X50-3160-00)TS450Scar_loc

The original Kenwood CAR UNIT board (X50-3160-00), installed in the TS450S and TS690S

The CAR UNIT do many different things in the TS450S/690S: from generating 3 different RF signals used as LO signals in the mixers.

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 functions of all ASIC’s YM6631/YM66312 and some peripheral circuits in only one chip !!



The XG 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.

xg_car_schDue the high performance of this FPGA the functions of the peripheral circuits (mixers, crystal oscillator, filters etc.) could be minimized to achieve a higher design flexibility of this board. Also the LO3 crystal oscillator was repleaced with a DDS, wich clock frequency was derived from the reference clock of 20MHz. This solution eliminates the TC1 as adjustment point for the LO3 frequency, originally present on the Kenwood’s car unit. 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:

XG_LO3_rbw100Hz_span200kHz XG_CAR_rbw100Hz_span200kHz XG_DLO1_rbw100Hz_span200kHzThe accurate design of all functions implemented in the FPGA for the communication with the TS450’s digital unit are high speed optimized and allow a glitch-free, smooth tuning operation.

The XG CAR UNIT board for the KENWOOD TS450S/690S:


  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 XG CAR UNIT board installed in a KENWOOD TS450S:


Installation notes:

Due to the high startup speed of the digital unit, a simple modification must be made on some TS450/690 to extend the CPU startup reset time for few milleseconds neccessary to give the XG CAR UNIT enough time to start. So add a polarized capacitor (4,7uF/16V) parallel to C13 on the digital unit:TS450_mod



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