Cat Kenwood Ts-850

 

Radio interfacing

Kenwood – PC interface with MAX232 – a classic

This simple interface replaces the original Kenwood\’s IF 232C. It is small and simple. I built lot of them housed directly in the DB25 shell. There is no special PCB layout, I used a scrap of universal PC board. A protective diode in the 8 -30 V lead is highly recommended.

No more details, just wire it and test (measure the input/output levels – see table below). If works, OK, if not, check for troublesome parts and joints in usual way.

 
 

 

An inexpensive optocoupled interface for Kenwood transceivers

To keep the noise and interference level as low as possible, there is a good isolation between radio and computer always a mandatory. Commercially available interfaces are expensive and quite large devices with a need of an external power supply. There is no guarantee of the separation and supply voltage leads with ground connections may cause RF loops. A very simple circuit which may be housed in a 25 pin Cannon connector package described OM3LU in the Slovak Ham Radio Magazine Radiozurnal.

Construction hints

A Radio Interface is generally a level converter (TTL/RS232). There are specialized ICs developed for such purposes (MAX 232, ICL 232) which ensuring proper levels. You should be warned that this interface does not ensure proper levels on both RS232 and TTL side. Otherwise, most interface circuit providing no RF isolation regardless of the optocoupler used – the RF path is closed through power supply unless the circuit is supplied from a battery. This interface provides RF isolation.

 

  • The transfer coefficient C TR of optocouplers may vary from 10 to 3000%, higher C TR have photo Darlington ones. Select one with C TR 100% or higher.
  • The circuit is supplied with voltage derived from the RTS (pin 4 of DB25 connector) signal of RS232 which should be measured across the 10 microfarad capacitor. There should be 10.5 V. Programs mostly activating the RTS signal so supplying voltage is present.
  • Voltage drop across 470 Ohms and diode in series is quite high. The resistor value may be varied down to 120 Ohms, the 1N4148 diode may be replaced with Schottky one.
  • The circuit is built into the DB25 shell. Use universal PC board for first trials. A custom made PCB is under evelopment.

Finally, the interface should be tested. Indicated values are valid for all kinds of Kenwood interface, not for this only.

Connect voltage to:

Measure:

0 V to radio pin 2 (TXD)

0 V on the computer serial connector pin 3 (RXD)

+5 V to radio pin 2 (TXD)

+10 V on the computer serial connector pin 3 (RXD)

0 V to radio pin 5 (RTS)

0 V on the computer serial connector pin 5 (CTS)

+5 V to radio pin 5 (RTS)

+10 V on the computer serial connector pin 5 (CTS)

-10 V to the computer serial connector pin 2 (TXD)

0 V or short RXD-GND on the radio connector pin 3

+10 V to the computer serial connector pin 2 (TXD)

+5 V or infinite RXD-GND on the radio connector pin 3

-10 V to the computer serial connector pin 4 (RTS)

0 V or short CTS-GND on the radio connector pin 4

+10 V to the computer serial connector pin 4 (RTS)

+5 V or infinite CTS-GND on the radio connector pin 4