Vhf Packet (F2 Mode) Operation - Yaesu FT-767GX Operating Manual

4.17 VHF Packet (F2 mode) Operation
The FT-767GX offers special features for pac-
ket radio operation on VHF or UHF, using the
FM mode of emission. You must determine, how-
ever, the AFSK signal levels provided by your
tnc (terminal node controller) for transmis-
sion, as well as the signal levels required by
the tnc for reception.
If your tnc has balanced AFSK tone output
(that is, without any added de-emphasis), con-
nect the AFSK signal from your terminal node
controller to the outer contact of the DATA
IN/OUT jack: impedance should be 600 ohms,
which corresponds with most tnes. Output sig-
nal level from the tnc should be set to
30mVrms.
1f your tnc has de-emphasis applied to the
AFSK output, the levels of the two tones will
be different, and must be re-balanced by pre-
emphasis in the FT-767GX. In this case you
can connect the AFSK signal from the tnc for
transmission to the PATCH IN jack (also 600-
ohm impedance), but you must also adjust the
tnc output level for 2mVrms maximum. The
PATCH IN audio connects in parallel with the
microphone audio input. A better solution is
to remove the de-emphasis, if possible, and
make connection as described in the preceeding
paragraph.
For receiving, there are also two available
output points for FSK, again depending on whe-
ther your tnc pre-emphasizes receive audio.
If the tnc can accept balanced tone levels
(such as the GLB PKT-1), connect the center
contact of the DATA IN/OUT jack to the recei-
ving input on the tnc: output level is 800mV
at 10 kilohms, so make sure your tnc can han-
die this high level (or add a 10k resistor to
ground and another in series to set the
level).
If your tnc requires unbalanced tones (and
includes its own pre-emphasis, such as the
TAPR TNC-2 and clones), use either the low-
level signal at the AF OUT jack (100mV at 10
kilohms), or the high level signal at the EXT
SP or PHONES jack.
Note, however, that using the EXT SP or PHONES
jack has two serious disadvantages: (1) plug-
ging into these jacks disables the loud-
speaker, making it impossible to monitor the
receiver (this is not recommended); and (2),
the AF gain and TONE control setting will
affect the packet input to the tnc.
The low-level signal at the AF OUT jack is the
best choice, as the receiver AF power ampli-
fier is bypassed. If your tnc attenuates the
receiver input for high level speaker audio,
you might wish to bypass that attenuation, and
then use the AF OUT jack.
Set the FT-767GX to the FM mode for VHF and
UHF packet (to be compatible with most other
operators using 1200 bits/sec on these bands),
and set the MONI, APF and NOTCH switches OFF
(out). Also, if you have the FTE-2 Burst Unit
or FTS-8 Tone Squelch Unit installed, make
sure the T ENC switch is OFF (out) and the SQL
control is not in the T SQL position. Recei-
ver tuning is as described for FM (84.16).
Use the memories to store the common packet
channels in your area, for easy recall.
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