[1000mp] PTT Interface

[Tom Homewood]

The simplest mod is to replace the Opto with a transistor, I used a 2N2222A
I think.  You do lose the isolation but that wasn't a problem for me.

Tom, W1TO


----- Original Message -----
From: "Carl Kratzer" <k3rv@usa.net>
To: <1000mp@mailman.qth.net>
Sent: Wednesday, December 25, 2002 7:47 AM
Subject: [1000mp] PTT Interface


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 interface
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 the
radio, which is +13.6 volts.  I am reasonably certain that I have eliminated
miswiring of the cable as the possible cause.  Apparently, the optoisolator
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 with
the
rear PTT/packet jacks?  Thanks in advance.

Carl, K3RV.

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