9 Packet-Radio
119
a few users are present but the distances are large then the longer but more robust
modulated packets can be used. In the opposite case, when many participants are present
but the average distances are smaller, then the faster/shorter packets can be used.
9.4
300 Baud HF-Packet
HF-Packet is activated with the command
Baud
.
pac:
B
300 <RETURN>
With this command the DSP is programmed for 300 baud Packet-Radio operation.
The QUAL and LOCK / TUNE :LEDs serve as tuning indicator. This tuning indicator is
only working when the signal to be decoded fits within an range of ± 200 Hz around the
center frequency. If the signal deviates more than ± 30 Hz from the correct frequency, the
QUAL LED is lit permanently
red
for
frequency too low
or the TUNE LED for
frequency
too high
. Carefully dialing the VFO knob into the
correct
direction decreases the
frequency offset. When the offset is below ± 30 Hz, the LEDs swap from
red
to
green
and
the TFC LED may become lit
green
when valid PR data is received (serves as DCD
indicator). If the user now continues to tune into the correct direction until the tuning
indicator swaps between LOCK and QUAL (or vice versa), the frequency deviation is
close to zero. In this case, LOCK and QUAL will slowly alternatively be lit
green
,
dependent on the fading conditions on the channel.
The audio output level for transmission is the FSKA value (refer to section
). from the
cmd:-
menu, as usually the HF transceiver is used for 300 baud HF-Packet
purposes and the settings from PACTOR/AMTOR are proper.
The 300 baud modem generally operates with 200 Hz frequency shift. The center
frequency is calculated automaticly from the tone-pair set with the
TOnes
,
MARk
and
SPAce
commands in the
cmd:-
menu. 100 Hz are added and subtracted respectively to
generate the modem tones. This may sound a bit complicated bus has the advantage that
all settings of the transceiver can be adopted from the PACTOR/AMTOR menu. But care
should be taken as a 500 Hz IF filter is already too small for Packet operation with 300
baud. It is only recommended to be used in the case that strong neighboring signals begin
to modulate the AGC of the transceiver.
9.5
KISS
KISS
means „Keep It Simple, Stupid“, which already implies the simplicity of this
interface protocol. In KISS mode, the PTC is degraded to be a pure “modem” and its
intelligence is limited to the physical protocol level (modulation, demodulation). All
higher protocol levels (e.g. AX.25) are processed on the PC or whatever the KISS-master-
system is. Hence KISS just acts as simple transport medium between the higher protocol
levels and the physical “modem” level. The “modem” does not have any knowledge any
more of the higher protocol levels.
3
KISS, Phil Karn, http://people.qualcomm.com/karn/papers/kiss.html