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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.
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Connect
voltage to:
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Measure:
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0 V to radio pin 2 (TXD)
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0 V on the computer serial connector pin 3 (RXD)
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+5 V to radio pin 2 (TXD)
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+10 V on the computer serial connector pin 3 (RXD)
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0 V to radio pin 5 (RTS)
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0 V on the computer serial connector pin 5 (CTS)
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+5 V to radio pin 5 (RTS)
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+10 V on the computer serial connector pin 5 (CTS)
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-10 V to the computer serial connector pin 2 (TXD)
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0 V or short RXD-GND on the radio connector pin 3
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+10 V to the computer serial connector pin 2 (TXD)
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+5 V or infinite RXD-GND on the radio connector
pin 3
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-10 V to the computer serial connector pin 4 (RTS)
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0 V or short CTS-GND on the radio connector pin 4
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+10 V to the computer serial connector pin 4 (RTS)
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+5 V or infinite CTS-GND on the radio connector
pin 4
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ICOM interfaces
There are another two interfaces for ICOM radios
with the CI-V bus. It should fit into a DB9 or DB25 shell. Not tested at
me (I am using Kenwood) but believe that it works. It may be built from
junk box parts, interesting is the absence of any supplying voltage -
both units are supplied with rectified RS-232 signals. A higher RF
immunity level to be expected.
Another Icom/Yaesu interface
This circuit appeared in an old magazine (source
unknown). The only info is that this interface does not work with 74HC04
- it must be 74HCT04. It does not need power supply, use it with program
which delives instant pulses at DTR pin.
Transistor Icom interface by OK2WY
Try this simplest one! More comments you may find at
OK2WY site.
I was unable
to test it because using Kenwood...
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