MFJ 432 Voice Keyer Interface
The MFJ 432 voice keyer
requires an interface cable to be used with
TR LOG. The control port
is really for a simple push button accessory box, and ties directly
into the voice keyer ISD1020A integrated circuit.
This interface circuit uses common
Radio Shack parts and
will provide DC/RF isolation between the PC and keyer by
using buffer logic and reed relays. Relays were used as the
MFJ 432 only requires a simple switch closure to activate
The buffer is the CD4050B non-inverting CMOS. The reed
relays are Radio Shack 275-232, 5 volt. Do not use the 5 VDC
provided by the keyer for this circuit. It will run on 4 to 5.5
volts provided by three AA batteries for DC isolation.
A handy project box is one of the A/B parallel port switch boxes
used for selecting computer printers, etc. They are metal, have
the DB25 ports already installed, and can be bought for less then
$8. Other options that use the PC parallel buss are CW, PTT,
paddle input and foot switch, all easily added to the project.
This simple interface has provided the isolation required for
a six transmitter multi-multi with networked PCs. Extensive
testing and multiple contests have produced zero failures.
73, --Rich KL7RA