SCS PTC-IIex, Manual

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8 FAX
All shift settings done via the control sequences changes the shift for the moment ( local ).
The value of the
Deviation
-parameters remains unchanged.
8.7.5 JVComm
Starts the JVComm modem of the PTC-IIex.
Arguments are only accepted to keep compatibility to the PTC-II, but are ignored.
8.7.6 FSK
Starts the NFSK-Modem. This is very similar to the FM-FAX demodulator. This detector
however is designed for a very much slower data rate compared to the FM-FAX detector.
The input bandpass-filter can be considerably narrower than that for FAX operation. The
base-band low-pass filter at the output of the demodulator may be changed to 200, 300 or
400 baud signal rate, by using the
FSKBaud
Parameters command.
The PTC-IIex is therefore highly suitable, when used in the MODEM operational mode
FSK as a demodulator for widely differing transmission methods. Packet-Radio with 300
Baud and multi-FSK systems such as PICCOLO etc. may be received when the
appropriate PC program is available. Also RTTY and AMTOR programs such as
Zorns
Lemma work very nicely when using the operational mode FSK. For this, as in all FM
modes, the data from the demodulator is available at PIN 6 of the RS-232 interface. It has
traveled via a trigger stage, which gives a 1-bit digitized signal as output. If the PTC-IIex
measures an input frequency of greater than 1900 Hz, then PIN 6 goes to -10 Volts. For
frequencies lower than 1900 Hz, the PTC-IIex sets PIN 6 to +10 Volts.
The NFSK-demodulator gives the measured frequency value to the RS-232 interface, at a
baud rate set by the
MBaud
command. The center frequency is here also 1900 Hz. This
frequency causes an output value of 128. A frequency range of
±
500 Hz gives an output
value of between 0 and 255. For frequencies outside this measurement range, the PTC-
IIex gives values of 0 or 255 whilst in FSK-MODEM operation. As in other FM-
MODEM operating modes, the tuning indicator indicates the output value directly.
For transmission using the NFSK-MODEM, refer to chapters 8.8 and 8.8.2 on page 105 .
8.7.7 Comparator
This MODEM command switches the PTC-IIex into the COMPARATOR mode. The
prefiltered receive signal, (filter bandwidth may be set with the
FResolut
parameter
command), is limited and transferred to PIN 6 (DCD) of the RS-232 interface. The RS-
232 port is, as in all other MODEM operations, still able to receive data. The
COMPARATOR operations may be aborted when a byte value of 255 is received by the
RS-232 interface, so that (for example) a correct de-initialization with
PTCFAX.EXE is
possible. The baud rate is also during COMPARATOR operation set to the value given in
the
Mbaud
command.
In practice it is only necessary to write a new INI file for PTCFAX.EXE that contains as
its last command
Comparator
. The INI file can also include the
FR
command to set the
required filter bandwidth (0-3).
The PC-program used must be configured to simple modem such as HAMCOMM or
COMPARATOR .
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