8 FAX
115
The following SSTV-modes are supported by the PTC-IIIusb:
SMode
MODE-Name
0 ALLMODE
1 MARTIN
1
2 MARTIN
2
3 SCOTTIE
1
4 SCOTTIE
2
5 SCOTTIE
DX
6
8 sec / 120 line
7
16 sec / 120 line
8
32 sec / 240 line
9 WRAASE
24/128
10 WRAASE
48/128
11 WRAASE
48/256
12 WRAASE
96/256
13 WRAASE
120/256
14 WRAASE
180/256
15 ROBOT
72/256
Table 8.2: STTV sub modes
8.8.11
TXcomp
Default setting: 0
Parameter: 0 COMPARATOR Tx disabled.
1 COMPARATOR Tx enabled.
This PARAMETER-command activates (1) or de-activates (0) the TXD-modulator in the
COMPARATOR mode. With
TXcomp
switched on, it is possible for many programs that
support the HAMCOMM-modem to send FAX and SSTV direct from the PTC-IIIusb.
The PTC-IIIusb looks at the voltage appearing on the CTS-line of the serial interface.
When CTS is active, the PTT line for the shortwave port is activated. The PTT line is de-
activated (turned off) with inactive CTS. When in the send condition, the PTC-IIIusb
measures the incoming data as square wave modulation data on the RxD PIN.
The zero crossing point is measured very exactly, and then modulates the
VCO
in the
DSP. The PTC-IIIusb has a very good transmit resolution even in the
Simple Modem
mode, providing the PC program works as precisely. The translation of the transmit-data
into a
clean
analogue signal is not just through an RC low pass filter (as is usual). Instead,
the system calculates exactly the reverse of the simple demodulator principle.
8.9
LED functions
The QUAL- as well as the TUNE / LOCK LEDs flicker green in the rhythm of the
received signal. An accurate tuning should be achieved by the software being used, e.g.
GETFax, which is a component of Airmail.
