AMTOR
45
If you want to initiate a call to another station using the 625 form of AMTOR, simply use the
AMTOR command with appropriate SELCAL:
AMTOR XDBUXAS
or
AMTOR 123456789
AMTOR ARQ (Mode A) operation requires that both station transmit alternately. First the informa-
tion sending station (the station actually sending data) sends three characters. This requires 210
milliseconds. This station then enters the receive mode and listens for the acknowledgment from
the information receiving station. The sending station will wait 240 milliseconds for the acknowl-
edge. After this 240 milliseconds delay, the sending station will again enter transmit and send the
next (or the same) three characters.
Since both stations are constantly switching from receive to transmit and back again, fast switch-
ing times are required for AMTOR ARQ operation. You can adjust TXDAMTOR to allow for the time
required for your station to change from receive to transmit, but you should allow a small extra
time for the other station to switch from transmit to receive. Regardless of the setting of this pa-
rameter, the total turn around time for one AMTOR data/ack cycle remains 450 milliseconds.
AMTOR Operation
There are three methods of entering AMTOR Mode of operation from the
cmd:
prompt, depending
on which mode AMTOR operation you wish to use.
Entering LAMTOR at the
cmd:
prompt will allow you to receive Mode A (ARQ) and Mode B (FEC)
AMTOR signals, but this mode does not support transmitting. If you are receiving Mode A AMTOR,
you may see repeated characters or miss characters completely, since you are not part of the link.
The two stations which are linked may be requesting retransmission (thus you see repeated char-
acters) or they may have received the character and you didn't due to band conditions. In this lis-
ten only mode, you may receive characters which do not meet the 4/3 space/mark ratio, or char-
acters which do not properly decode in the AMTOR character set. These will be displayed on your
screen as the MISSCHAR which is defined in your
KAM
.
The second method to enter AMTOR operation is to use the FEC command, which places you in
the Mode B receive. In this mode you may receive FEC transmissions, and you can enter the trans-
mit mode by issuing the
Ctrl-C T
directive. You can then enter any text you wish sent from the
keyboard and return to receive mode with the
Ctrl-C E
directive.
The FEC command is also used to initiate a SELFEC transmission. Entering FEC with a SELCAL
(
F
ec
xxxx
[
xxx
]) will automatically enter the transmit mode of FEC and send the xxxx[xxx] SELCAL
to start the designated stations receive system. You would then send your message, returning to
receive with the
Ctrl-C E
directive. In order to enable your unit to receive only SELFEC signals, you
must turn AUTOSTRT ON. Once you have started receiving, you will stop upon the end of the
transmission or upon losing lock with the FEC signal.
To enter the Mode A AMTOR operation you use the AMTOR command. Using the command
AMTOR xxxx
[
xxx
] (where
xxxx
[
xxx
] is a selcal) will cause your
KAM
to attempt to establish an ARQ
link to the station with SELCAL xxxx[xxx]. If you simply enter
AMTOR
you will enter a standby re-
ceive mode, in which you will be able to receive FEC transmissions or your unit will respond to an
ARQ call. You can enter the FEC transmit mode from this standby condition, enabling you to call
CQ by using the
Ctrl-C T
directive. This puts your
KAM
in FEC transmit and any characters you
type will now be sent in FEC Mode. After you've entered your CQ message, you can use the
Ctrl-C E
directive, which will return you to the AMTOR standby mode after the transmit buffer is