[1000mp] PTT Interface

[Carl Kratzer]

Has anybody used an optoisolator circuit to activate the PTT line on the =
rear
of the radio, using either the RCA jack or the PTT line in the "packet"
connector?  I tried to interconnect a Rigblaster NOMIC sound card interfa=
ce to
the rear panel "packet" connector on my Mark V Field.  After considerable=

experimentation, I determined that, while the rigblaster would work fine =
on
the front-panel mike connector (whose PTT line is approximately +6 volts)=
 as
well as the CW jack, it would not activate the PTT line on the rear of th=
e
radio, which is +13.6 volts.  I am reasonably certain that I have elimina=
ted
miswiring of the cable as the possible cause.  Apparently, the optoisolat=
or
circuit in the rigblaster NOMIC is not compatible with the higher voltage=
 PTT
line on the rear of the Mark V Field.  The circuit used in the NOMIC is a=
 4N33
optoisolator driven by RTS or DTR line from PC serial port through diode =
and
680 ohm resistor.  The output side of the 4N33 has a floating base lead, =
with
the emitter and collector leads used to key the radio PTT.

Any suggestion for a simple mod to the circuit to allow compatibility wit=
h the
rear PTT/packet jacks?  Thanks in advance.

Carl, K3RV.          =