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USER'S GUIDE
3.4.
Operating techniques on ARQ
3.4.1.
Transmitter and receiver tuning
An ARQ contact always starts with the master station making the initial call, and the slave
replying. Thus the frequency will have been chosen by the master station, and the slave
station will have 'netted' onto that. It often happens that an offset at either station will
then result in the signal from the slave received at the master being a bit off tune. If the
master station then readjusts his transceiver main tuning dial to remedy this error, he will
also offset his transmitter, probably putting his signal off tune in the distant slave's re-
ceiver. A never ending series of readjustments can then take place. The equivalent prob-
lem on other modes rarely causes trouble since the retune operations only take place
each time the transmission is passed from one station to the other. However, with the
'quick-break' operation of ARQ, such offsets can cause trouble. Thus a convention has
been adopted among AMTOR operators to prevent this situation arising.
This convention is that the master station must at all times keep his transmitter frequency
constant. Thus if the master finds that the slave signal is not correctly tuned, he must ad-
just only his receiver frequency to remove the error, leaving his transmitter frequency un-
touched, by the use of the RIT control on the transceiver. The slave station, on the other
hand, may, if he finds his receiver off tune, make a correction by adjusting both receiver
and transmitter frequencies together, by means of the main tuning dial.
This convention prevents any offset from accumulating, and is the frequency-domain ana-
logue to the time-domain synchronizations in which the master station clock determines
the phasing for the contact.
3.4.2.
Changing frequency during an ARQ QSO
Since both stations are 'listening-through,' if there is some interference on the frequency,
or if a change of frequency is desirable for some other reason, for example, to clear a call-
ing frequency, then both stations may wish to move together to another frequency.
Whilst at first there may seem to be no reason to discuss such a simple operation, which
is very common and easy to perform on any other mode, there are problems if a QSY is
made in some ways in ARQ, and there are advantages in adopting a specific technique.
3.4.2.1.
The easiest way of QSY-ing an ARQ QSO is to close it down, and restart it again on a
new frequency, with the master station choosing the new frequency. This is referred to
in AMTOR circles as a 'cold' QSY. This technique is the preferred one when moving off a
calling frequency, and in other conditions where there is good copy between both sta-
tions, so that an orderly close-down and start-up is anticipated.
3.4.2.2.
If, however, the QSY is desired because of interference, then another technique is pos-
sible, and if carried out in the right way, can have decided advantages, but if carried
out wrongly, can cause problems and offence to other band users. This is referred to as
the 'HOT' QSY technique.
In this, the master station, while in the re-phasing mode, moves off the old frequency
to the new one, and the slave then follows. It is important, while the master station is
doing this, for him to prevent his transmitter from radiating, in order to prevent unin-
tentional interference to other band users, and also to disable the connection between
the receiver and the AMTOR, in order to prevent unintentional 'phantom sync.' to any
other ARQ signals which may be audible during the search for a new frequency. Such
phantom sync will result in spillage of traffic from the QSO in progress, or from the oth-
PK232UG Rev. E 9/87
AMTOR OPERATING SUGGESTIONS FROM G3PLX
D-4
182
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