Kantronics MT1200, User Manual, Page: 136 / 157

Many transceivers, especially most hand-held models, obtain Push-To-Talk keying by
completing a circuit between the mic input and PTT ground. A direct PTT input to the
mic input line of units with this type electret condenser microphone is not usable without
some type of isolation.
If you plan to operate with a hand-held transceiver, the MT1200 has incorporated an
isolation circuit which is available by positioning jumper J4 on the center post and the
left post (labeled HT) as you face the front of the MT1200. Should you later use a
different type radio, this change may need to be reconfigured by placing the J4 jumper
on the center post and the right post. Most other radios of current manufacture will not
require any modification of the MT1200.
You may also interface to a hand-held without performing this modification by
incorporating the same type of circuitry in the external cable between the MT1200 and
your hand-held. Ground return and speaker audio, are both supplied through the
external speaker jack of your hand-held. While you will need to check the exact
requirements of your hand-held radio, the following guidelines may be useful:
•
A 0.1
µ
F capacitor (non-polarized) usually is required in series in the transmit
audio line from the TNC to any handheld transceiver (HT) radio. Even if a
capacitor is not required for connection to a particular radio, it can still be
installed, and transmit audio (packets) will pass through to the radio.
•
ICOM HT radios key the PTT by providing a low impedance path from the mic
input to ground. To accomplish this, simply install a resistor (approximately
3.9 k
Ω seems to be a good value) in series with the PTT wire from the
MT1200, and connect this to the mic input along with the AFSK line.
➔ The ICOM 2A style wiring is most common, and can be used with some
Alinco, Azden, and standard HTs.
•
YAESU and Radio Shack HTs are similar but use a mono plug and a 2.2 k Ω
resistor.
•
Most KENWOOD HT radios key the PTT line by connecting the sleeve of the
mic connector to the sleeve of the external speaker connector. This means
that you will not need a resistor in the PTT wire from the MT1200, simply
connect the PTT wire to the sleeve of the mic connector. Another point to
watch: most of the KENWOOD HTs (2600 and later) use a three pin mic
connector. The AFSK from the MT1200 should therefore connect to the RING
and not the TIP of the mic connector.
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