Digital Modem Interfacing (Tnc, Weatherfax, Etc.) - Yaesu FT-920 Operating Manual

2. Digital Modem Interfacing
(TNC, WeatherFax, etc.)
The FT-920 provides several convenient interconnec-
tion points, as well as dedicated operating modes,
for digital operation. While interfacing to commonly-
available modems is simple and straightforward, it is
important that you read the instructions below so as
to understand the facilities that are provided on the
FT-920.
DATA Jack
This five-pin DIN connector is the primary interface
port for most digital-mode operation. It provides the
following connection points which may be required in
your installation:
Pin 1 (AFSK Input):
Connect this pin to your TNC's "AFSK Out" or "Mic
Audio" output line. The optimum input level is 30
mV rms, and the input impedance is 3 k . Your
TNC's audio output level potentiometer will allow
you to set the level to the optimum value. This pin
may be used either for 300 baud SSB-mode digi-
tal operation or for 1200-baud FM packet. The
bandwidth and frequency response are not, how-
ever, suitable for 9600 baud operation. Be sure
the AFSK-FSK switch on the rear panel is in the
AFSK position.
For FSK operation (whereby the TNC closes a
line to ground to accomplish teletype keying), set
the AFSK-FSK switch to FSK, and connect your
TNC's FSK keying line to Pin 1.
16
Pin 2 (Ground):
Connect this to the shield(s) of the cable(s) used
for connections between the TNC and the FT-920.
Pin 3 (PTT):
Connect this pin to the PTT line from the TNC.
This pin, when grounded by the TNC, places the
FT-920 into the Transmit condition.
Pin 4 (Audio Out):
Connect this pin to your TNC's "RX Audio" input
line. This is a constant-level (100 mV rms @ 600
) audio output line which is not affected by the
position of the front-panel AF G
Pin 5 (BUSY):
This is a "Squelch Status" pin not generally re-
quired for digital mode operation. This pin is held
at +5V when the squelch is open, and is grounded
when the receiver is muted by the squelch ("no-
signal" condition).
K Jack (Rear Panel)
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If you wish to send CW using your TNC and com-
puter keyboard, the CW Key output line from your
TNC may be connected to the rear-panel K
according to the connection information provided on
page 5.
Since a TNC's keying output is electrically similar to
that of a Straight Key, set the rear panel's P
switch to the P (Manual Key) position, and connect
DL
the TNC's key line there. You can still connect your
keyer paddle to the front panel K
FT-920's built-in electronic keyer, for those situations
where you wish to send using the paddle; there is no
need to switch the internal keyer on and off.
FT-920 Operating Manual
control.
AIN
jack,
EY
-K
DL EY
jack, and use the
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