HAND-HELDS
18
Interfacing Hand-Held Radios
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 KAM, KPC-2 and KPC-4 have incorporated
an isolation circuit which is available by jumper positioning. Should you later use a different type
radio, this change may need to be reconfigured. Most other radios of current manufacture will not
require any modification of the TNC.
You may also interface to a hand-held without performing this modification by incorporating the
same type of circuitry in the cable from your TNC to your hand-held. Ground return and speaker
audio are both supplied thru the external speaker jack of your hand-held.
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 seems to be a good value) in series
with the PTT wire from the TNC and connect this to the mic input along with the AFSK line.
ICOM Mic Connector
YAESU radios are similar but use a mono plug and a different resistor-
YAESU Mic Connector
Most KENWOOD HT radios key the PTT line by connecting the sleeve of the mic connector to the
sleeve of the earpiece connector. This means, that you will not need a resistor in the PTT wire
from the TNC, simply connect the PTT wire to the sleeve of the mic connector. Another point to
watch – most of the KENWOOD HTs (2500 and later) use a three pin mic connector. The AFSK
from the TNC should therefore connect to the RING and not the TIP of the mic connector.
KENWOOD Mic Connector
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