8 FAX
110
8.6.7
Comparator
This MODEM command switches the PTC-IIIusb into the COMPARATOR mode. The
prefiltered receive signal, (filter bandwidth may be set with the
FResolut
parameter
command), is limited and is available as virtual DSR signal in the USB data stream. The
interface is, as in all other MODEM operations, still able to receive data. The
COMPARATOR operation will be aborted when a byte value of 255 is received. The
baudrate is also during COMPARATOR operation set to the value given in the
Mbaud
command.
The PC-program used must be configured to simple modem such as
HAMCOMM
or
COMPARATOR
8.6.8
PTC-IIIusb with 300 baud HF Packet
This mode still exists just to achieve compatibility with the first PTC-II modem. The
much better and recommended way to operate 300 baud Packet is with the new 300
baud mode in the
pac:
menue. Refer to chapter
on page
300 Baud Packet operation is possible with the PTC-IIIusb when using the program
TFX
in addition.
TFX
is started on the PC as a TSR program (memory resident) and discretely
operates the packet protocol in the background. The PTC-IIIusb itself operates as a
modulator/demodulator in this case, such as
BayCom
or
PC-COM
. The combination of
PTC-IIIusb and
TFX
emulates a
real
hostmode TNC for 300 baud Packet that can be
operated with a hostmode terminal program such as
GP
. The command
PR300
starts the
TFX
compatible 300 baud PR modem.
TFX
should be used with
hardware DCD
turned on. The MARK tone is the one also
valid for PACTOR and the SPACE tone is always located exactly 200 Hz below the
MARK tone.
The
TFX
program is available at nearly every Packet-Radio mailbox or in the internet at
http://www.nordlink.org
8.7
Transmission during MODEM operation
In every MODEM-operational mode, independent of if it is AM-FAX, FM-FAX, SSTV
or FSK, the PTC-IIIusb keys the transmitter (PTT becomes active) when it receives bytes
with a value between 0 and 63. The transmitter stays on for exactly 166.7 ms after
receiving each
transmit-byte
. If the PC program sends the transmit data appropriately fast,
then the transmitter stays in the transmit condition. If the data does not change within the
166.7 ms (for example when in FM-FAX only
white
must be transmitted), then the PC
program must send data to the PTC-IIIusb at least every 166.7 ms, so that the transmitter
stays on transmit. By using this system, an extra PTT-command is not required.
The maximum transmit amplitude is set using the
FSKAmpl
in the main menu. It is not
necessary for any new setting to be undertaken, and can be left at setting for PACTOR or
RTTY.
2
Be aware that Internet addresses frequently change