SCS PTC-IIex, Manual

Page: 129 / 220

9 Packet-Radio
modulated packets can be used. In the opposite case, when many participients are present
but the average distances are smaller, then the faster/shorter packets can be used.
9.4 300 Baud HF-Packet
In deviation to the PTC-II the PTC-IIex is capable to operate 300 baud Packet-Radio
directly, without the need to use support-programs like
TFX as described in section 8.7.8
on page 105 .
HF-Packet is activated with the comand
Baud
.
pac:
B
300 <RETURN>
With this command the DSP is programmed for 300 baud Packet-Radio operation and the
tuning display is activated. The special mode of the tuning display here allows the
received signals be tuned with an accuracy of 10 Hz. The red LED signalizes the current
symmetry of the discriminator (demodulator). In receiving condition this LED should
ideally represent the middle of the tuning bar. With selective fading (Multipath) the LED
may deviate more or less, which has nothing to do with frequency deviations.
The audio output level for transmission is the FSKA value (refer to section 6.42 on page
55 ). 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, SMACK and SRP for Packet-Radio Operation
9.5.1 KISS
KISS
4
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.
Because of this, KISS is not suitable for e.g. PACTOR: The timing-critical PACTOR
protocol cannot easily be implemented on a PC with multitasking operating system and
transported via a KISS interface to the modem.
Via KISS only Packet-Radio modems
4
KISS, Phil Karn, http://people.qualcomm.com/karn/papers/kiss.html
115