SCS PTC-IIex, Manual

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8 FAX
disappears. The value 63 causes the maximum amplitude to be generated (that set by the
FSKAmpl
command). The transmit data controls the signal processor directly and
without delays. The transmit signal bandwidth is also not limited through any hardware
filter.
8.8.2 Transmission in FM-FAX/FSK/SSTV-Modem mode
For transmit operation in all FM variants, a constant amplitude signal is generated (that
set by the
FSKAmpl
command), the frequency of which relates to the transmit data
amplitude. The transmitted data controls the instantaneous frequency of the output signal.
For the value 0, the PTC-IIex generates a frequency of 1500 Hz. The value 63 produces a
frequency of 2300 Hz. Values between these limits produce the appropriate frequencies
between 1500 and 2300 Hz. The frequency modulator in the DSP operates phase-
continuous, and therefore produces a very clean and spectrally narrow signal. An output
bandpass filter has thus been omitted.
The steepness of the frequency modulator is independent of the
Deviation
parameter,
or other settings. The maximum possible shift of the transmitted FSK signal however is
thus limited to 800 Hz.
In order to generate the synchronization signal below 1500 Hz, the PTC-IIex must
understand (as stated in the JVFAX-standard) three further bytes outside the 0-63 as
transmit-data:
125 (dec.) generates the frequency 1100 Hz.
126 (dec.) generates the frequency 1200 Hz.
127 (dec.) generates the frequency 1300 Hz.
8.8.3 Transmission in COMPARATOR mode
The transmission using the COMPARATOR MODEM is controlled with the
TXcomp
parameter (please refer chapter 8.9.11 , page 110 ). If
TXcomp
is switched on, the
handshake line CTS is used to control the PTT line, and the RxD PIN of the port supplies
the transmission data. This method provides a very clear transmission signal, but has to be
supported by a corresponding PC program.
If
TXcomp
is switched off, the PTT control via the CTS line is ignored. The transmission
is completely handled by the PC program. As modulation signal, the audio signal of the
PC speaker is used. However, this method is usually not recommended and hardly needs
to be used.
8.9 The Parameter commands in detail
8.9.1 AGain
Default setting: 50
Parameter: X 1... 200, amplification factor for AM-FAX.
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