SCS PTC-IIex, Manual

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8 FAX
deteriorates the synch recognition, but however, does allow unknown SSTV-
transmissions to be processed without problem when a good signal to noise ratio is
available.
The PTC-IIex uses the standard given in the JVFAX documentation, to pass the
recognized synchronization pulses to the PC program. In the JVFAX configuration, the
position
LSB-SSTV-SYNCH must be set to YES . The JVFAX program and PTC-IIex
use the lower two bits of every byte sent to the JVFAX program to signal the synch
pulse. Bits 0 and 1 are set to 1 in the resting state. As soon as the PTC-IIex recognizes a
correct synch-pulse on the 1200 Hz frequency, it sets the bits 0 and 1 to 0 for the time the
synch-pulse occurs. (Note: the VIS code is at present not processed by the PTC-IIex, and
therefore bit 2 is actually redundant for the signaling condition.) The small decrease in
color resolution caused by only having 6 bits to signal brilliance information can, in
practice, be ignored.
The JVFAX synch method used by the PTC may be turned off using the
JSynch
parameter command. In theory, the PTC-IIex may be used with the JVFAX in the
operational condition
LSB-SSTV-SYNCH NO . Then the system uses the full 8 bit data
width for picture information. The practical results however speak against using this
method.
With the
JSynch
parameter turned on (default setting), the recognized synchronization
pulse is signaled to the user by using LED´s:
A vertical synch-pulse (picture new start) lights the Connected-LED shortly.
A small time offset of the line-synch pulse may be set by use of the
HSynch
parameter.
This allows the whole picture to be shifted slightly left or right.
For transmission use when in SSTV-MODEM operation, refer to chapter 8.8 , page 105 .
8.7.4 Jvfax
Starts the JVFAX mode. This mode does not contain its own Modem as such. Instead, it
offers a sort of "
springboard " to FM-FAX, AM-FAX and SSTV by using special control
sequences, that are recognized in this mode by the PTC-IIex. Directly after switching to
JVFAX operation, the PTC-IIex is in Modem mode FM-FAX, using a shift which has
been preset using the
Deviation
parameter (normally 400 Hz.
The following 1-Byte commands are accepted by the PTC-IIex 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
103