SCS PTC-IIex, Manual

Page: 115 / 220

8 FAX
8.5 The PTC-IIex as COMPARATOR-MODEM
The PTC-IIex is capable to be used as a simple COMPARATOR-Modem. This allows
compatibility to all at present available RTTY/FAX/SSTV programs that allow use of a
simple modem (e.g. HAMCOMM modem). The operation as a COMPARATOR is
completely different to that of the other MODEM variants of the PTC-IIex. In the normal
MODEM operation (
Amfax
,
Fmfax
,
SSTV
commands), the DSP undertakes the
demodulation of the signal itself, and uses relative complex algorithms. In the
COMPARATOR mode, it is only used as an adjustable pre-filter (bandpass filter, Fresol
command). The prefiltered signal is then only hard limited, and passed to PIN 6 (DCD) of
the RS-232 interface. The actual demodulation must be undertaken by the PC program, so
that considerable differences in quality may occur.
8.6 PTC-IIex with 300 baud HF Packet
This mode has been left available for compatibility purpose with the PTC-II. Much
more comfortable you operate 300 baud Packet-Radio using the
pac:- menu. Refer to
section 9.4 on page 115 .
300 baud Packet operation is possible with the PTC-IIex when using the program TFX in
addition. TFX is started on the PC as a TSR program (memory resident) and discretely
operates the packet protocol in the background. The PTC-IIex itself operates as a
modulator/demodulator in this case, such as
BayCom or PCCOM . The combination of
PTC-IIex and TFX emulates a real hostmode TNC for 300 baud Packet that can be
operated with a hostmode terminal program such as GP. The command
PR300
starts the
TFX compatible 300 baud PR modem. Multitasking is disabled in this case, therefore no
VHF/UHF Packet connect is possible at the same time. The LED´s are set to medium
brightness, i.e. the
BRightness
command is also disabled.
8.7 Modem commands in detail
Only activate the MODEM commands using the support program PTCFAX.EXE . If
somebody tries to call for example SSTV out of PlusTerm , he will be punished with
the output of a never ending data stream of hex characters
☺
8.7.1 Amfax
Starts the AM-FAX-MODEM. The measured amplitude of the 2400 Hz tone frequency is
given over the RS-232 interface at the rate set using the
MBaud
command.
The time-resolution required, and filter bandwidth may be pre-set using the
AResolut
parameter. The internal amplification may be pre-set using the
AGain
parameter. The
output values reach from 0 to 255. Measured values greater than 255 are limited to 255 by
the PTC-IIex. (The data width is limited to 8 bits by the serial format.) With an AF input
amplitude of 500 mV, and a standard setting of
AGain
(50), the PTC-IIex gives an
output value of 255. With an input of 250 mV the output value is appropriately 128.
The tuning indicator displays the output values. The lower signal values lie to the left, the
greater to the right.
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