Using The Controls - Raytheon Pathfinder 1200 Instruction Manual

2.3 USING THE CONTROLS
2.3.1 TUNE Control
The magnetron and the Gunn oscillator may take about 10 minutes to completely
stabilize on frequency. So after switching on and tuning initially, the tuning should be
rechecked after the first 10 minutes.
Symptoms that the equipment may be out of tune are a lack of distant echoes or the
appearance of double echoes (one echo behind another). The coarse method of tuning
is described in Section 5. Normally it is possible to fine tune the radar by selecting a com-
paratively weak echo and then rotating the TUNE control until the strongest echo and
best definition are combined.
2.3.2 GAIN Control
The correct setting of the GAIN control is for light background speckle to be just
visible on the screen. The equipment is then in its most sensitive condition. Objects will
be detected at the greatest possible range. With too little gain, weak targets may be missed
and there can be a decrease in detection range. With excessive gain (a few) extra targets
may be brought in, but the contrast between echoes and background noise will be sub-
stantially reduced, making target observation more difficult.
In crowded regions gain might be temporarily reduced to clarify the picture. This
must be done with care since important marks may be missed. With gain at its normal
setting, clutter from rain or snow may obscure the echo from a ship inside a squall or
storm. A temporary reduction in gain will usually permit the stronger and more distinct
ship's echo to be distinguished.
Detection of targets beyond the storm may, however, require slightly higher gain than
normal, since the clutter may have attenuated, but not completely obscured, echoes from
the targets. The GAIN control should be always returned to its normal position as soon as
any temporary alteration is no longer required.
2.3.3 SEA CLUTTER Control
Whereas the GAIN control affects the strength of echoes at all ranges, the effect of
SEA CLUTTER control is greatest on short-range echoes, becoming progressively less as
range increases. The SEA CLUTTER control is only effective up to a maximum of about
three miles.
In particular, the SEA CLUTTER control reduces the strength of the mass of random
signals received from waves at short range. The setting used should be sufficient to reduce
the strength of signals until clutter appears only as small dots, and until small targets can
be distinguished, the setting should never be advanced so far as to blank out all clutter.
The sensitivity of the SEA CLUTTER control is fully variable, thus enabling an
optimum picture to be obtained under adverse weather conditions.
Maximum reduction in the strength of close-range echoes takes place when the control
is turned fully clockwise. When it is turned counterclockwise there is no reduction in
the strength of echoes.
The SEA CLUTTER control may be used to reduce some rain or snow clutter, as well
as strong sea clutter, in the immediate vicinity of the vessel. A temporary increase in the
setting will usually permit strong echoes from ships, and most navigational marks inside
storms or squalls, to be distinguished.
At close range in crowded regions the control may be temporarily advanced to clear
the picture. This should be done with care, so as to avoid missing important echoes.
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