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8 FAX
109
The following
1-Byte commands
are accepted by the PTC-IIIusb when in JVFAX mode:
Byte
Function
$49: Switches
to
AM-FAX
$4A: Switches
to
AM-FAX
$4B: Switches
to
SSTV
$41:
Switches to FM-FAX with 150 Hz shift
$42:
Switches to FM-FAX with 200 Hz shift
$43:
Switches to FM-FAX with 300 Hz shift
$44:
Switches to FM-FAX with 350 Hz shift
$45:
Switches to FM-FAX with 400 Hz shift
$46:
Switches to FM-FAX with 500 Hz shift
Table 8.1: JVFAX Control Bytes
All shift settings done via the control sequences changes the shift for the moment (
local
).
The value of the
Deviation
-parameters remains unchanged.
8.6.5
JVComm
Starts the JVComm modem of the PTC-IIIusb.
Arguments are only accepted to keep compatibility to the PTC-II, but are ignored.
8.6.6
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-IIIusb 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.
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-
IIIusb gives values of 0 or 255 whilst in FSK-MODEM operation.
Additionally, as in all FM modes, the data from the demodulator is available as virtual
DSR signal in the USB data stream. It has passed a trigger stage, which results in a 1-bit
digitized signal as output. If the PTC-IIIusb measures an input frequency of greater than
1900 Hz, the virtual DSR goes active. For frequencies lower than 1900 Hz, the PTC-
IIIusb sets the virtual DSR to inactive.
For transmission using the NFSK-MODEM, refer to chapter
, page