DXBANDSW band decoder project
controls Yaesu Quadra VL1000 bands from Kenwood TS850 CAT

Last update October 13,2015

I have purchased a 2nd hand amplifier Yaesu Quadra VL1000. I tested it first with FT2000 - it works fine, Yaesu radio and Yaesu amplifier can talk to each other, amplifier band/antenna/tuner switching is automatic. Problem starts when you try to connect the amplifier to radio of another manufacturer. When you don't supply band data signal to amplifier, you have to use F-SET procedure every time you change the band (it includes to transmit a carrier and press button on the amplifier) that is not very smart. One way is to use a switches that supply band data (for example BCD switch that gives TTL level output). This solution is better, but still... Ever better is to get band data from transceiver directly. I want to use Kenwood TS850 radio - rather old model, but it still works fine so I would like to keep it on my desk further. Some people take band signal from the radio directly - it is there, but not connected to any connector, you have to modify the radio. I wanted to go by different way...
I decided to design a simple board with AtMega8 chip that should read the frequency from the radio using CAT, identify the band and set the band data output. Additionally (to make the interface more general) I added a possibility to select band manually using buttons (for example when I operate with different radio or without CAT) and display the band using 7segment display. The goal is also to allow operation with or without transceiver control software (for example, when I run a contest, the CAT communication is controlled by contest software - in this case the controller just listen to data exchange between radio and contest software; when the PC is disconnected, the controller becomes active and asks for frequency information on its own). For this reason there is a selector that switches data sent to radio between RS232 port and controller.
The MCU stores last band in EEPROM, so that band is always active on subsequent power up.
There are 2 band data inputs on VL1000, each related to each transceiver input. I use the round connector, correesponding to input number 1.
The band decoder should work with all Kenwood radios that use TTL levels at CAT port (I have tested TS850, but should work with TS450 and TS950). Data speed is fixed to 4800 8N1 (standart for Kenwood radios).
I don't expect somebody to build his clone (the TS850 is quite old model, mine is already 24 years old), but it can serve as an inspiration...

Here is the block & circuit diagram

Some pictures of prototype

Here are the files - circuit diagram, PCB layout and assembler source code..

Contest programs

I have analyzed the protocol and tested it with CT, Wintest and N1MM contest software. It is interesting to see how the communication works. CT sends at startup command AI1 (subscribe), that starts automatic sending of IF message upon any change of transceiver. It works fine, but when the TCVR is power off/on while contest program running, the connection is lost. Wintest and N1MM don't relay on AI, but periodically request IF message (polling mode). In case the split mode is active, other VFO frequency is requested as well (command FA and FB). The decoder uses polling mode as well, just introduce timeout on IF message - when IF is not received for certain time, the MCU request it on its own. Special handling is done for split mode (the MCU is always interested in TX freq, not RX). See TS850 external control instruction manual for details.

73 OK1DX