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TS-850S Interface

Kenwood TS-850S to Yaesu FL-7000 band data interface board.

by John Mattesini Jr. - AA3M

I recently purchased the FL-7000 amp and quickly realized what a shame it was not to take advantage of all the features the Yaesu folks designed into the unit. The amplifier will not only change bands, it will remember the settings of it's built-in antenna tuner for each band. With the optional FAS-1-4R remote switch, it will also switch to one of four antennas for each band setting. I was primarily interested in finding an inexpensive (cheap) interface to have the band data information of the Kenwood drive the Yaesu amplifier. Slight problem. The Kenwood TS-850 was designed to "talk" externally via it's RS-232 serial connection. The Yaesu "talks" Yaesu band data format. Basically a binary representation of a value 1 through 9.

The amplifier is fairly sophisticated with a microprocessor controlling the amplifier's main functions, and another dedicated to the autotuning function. Serial communication with the outside world was not seen as a necessity at the time it was designed.

The unit will work quite nicely with most other Yaesu transceiver models with their band data connections conveniently brought out to an accessory connector. There are third party interface units which will read the Kenwood serial data port, and convert the data to the required Yaesu binary band data format. Needless to say they cost quite a few dollars.

I did more research and discovered where another amateur, Winfried DK9IP, clearly illustrates how he connects to the 850's filter unit to bring out the nine outputs representing the band data information. (I hope he doesn't mind me providing this link to his page illustrating that process.)

Here's the link to his site: http://www.dk9ip.de/DK9IPprojects/DK9IPdecod/dk9ipdecod.html

What I did was to copy that aspect of the process, and build an interface which converts the 9 states representing band data, and convert that to the binary format required by the Yaesu FL-7000 amplifier.

Here's a photo of the bare board...

A photo of the completed board...

The board installed in the TS-850S...

The board layout in .pdf format... (63.5 K)

The schematic in .pdf format... (15.8 K)

I designed the board to be as simple as possible to assemble. All the components are of the same value. There is a total of 13 transistors, 22 resistors, 4 diodes, 4 relays and the CD40147 IC. That's it! If you have to order the parts, you're going to have to wrestle with the fact that 22 resistors will cost you $1.76 while the same ones in quantity of 200 will cost you about $2.80. Bulk pricing....

Here is the parts list in .txt format...

Yaesu FL-7000 Kenwood TS-850S Band Data Interface Parts List (1 K)

One diversion from Winfried's installation I want to attempt, is to find a replacement Molex plug for the antenna tuner that you set aside to make room for the DB9 on the rear panel. If I can find a Molex to replace it, I'll use that one to bring the band data out of the same hole of transceiver's rear panel. You only need five pins for the interface to the Yaesu amplifier. Using the six pin Molex, you will even have one to spare.

You may have noticed I also have a pico-fuse as a last -minute thought. I'll add it to the board layout on version #2.

As with most of these home-brew projects I have a few circuit boards left over. If anyone is interested I can put together a kit which would include the board, parts, and shipping for $55 US.

To purchase a kit or if you're interested in more info before it's posted, you can reach me at

73 John AA3M