Dealing With Interference - Yaesu FT-1000 Operating Manual

4. Operation - Dealing with Interference
Dealing with Interference
The FT-1000 includes a wide range of special fea-
tures to suppress the many types of interference that
may be encountered on the hf bands. However, real
world interference conditions are constantly changing,
sO optimum setting of the controls is somewhat of an
art, requiring familiarity with the types of interference
and the subtle effects of some of the controls. Therefore
the following information should be considered only as
general guidelines for typical situations, and a starting
point for your own experimentation.
The descriptions of the use of each control are
arranged in the order that you would usually make them
after changing bands. The possible exception to this is
if strong pulse noise is present, such as from the
"Woodpecker", in which case you may need to activate
the noise blanker (described on this page) before you
can make other adjustments.
Front End Selection
Perhaps the most important consideration for op-
timum receiver performance, after you have selected a
particular band, is the receiver front end selection, The
best selection will depend on background noise at the
time, the presence or absence of strong signals, and
whether or not you want to hear very weak signals. If
the front end is set for too much gain, background noise
will make listening difficult, and very strong signals on
other frequencies may cause intermodulation interfer-
ence, masking weaker signals. On the other hand, if the
front end is set for too little gain (or too much attenua-
tion), very weak signals will not be heard.
The NOR setting of the FRONT END selector activates a
constant-gain, quad push-pull FET amplifier for maxi-
mum sensitivity. However, if background noise causes
the S-meter to deflect on clear channels, turn the FRONT
END selector clockwise until the S-meter drops below
S-1 (the white area at the left end of the top meter
scale). This setting optimizes the trade-off between
sensitivity and interference immunity. Also, once you
have tuned in a station you want to work, you may want
to reduce sensitivity further (or add attenuation) by
turning the FRONT END control to a more clockwise
setting. This can make reception of the desired station
more comfortable, important especially in long QSOs.
RF Gain Setting
When tuned to a moderate strength signal, if low
level background noise is still present after setting the
FRONT END selector, try reducing the RF gain control
from the fully clockwise position, This reduces the
signal input to the first mixer via a PIN diode attenuator
page 22
and causes the minimum S~-meter reading to move up
the scale, often clearing up the background noise and
putting the desired signal more "in the clear", Remem-
ber, however, to return this control fully clockwise
when you want to receive weak signals, or read low
levels on the S-meter. See also the Note box below.
AGC (Automatic Gain Control) Selection
When tuning around the band looking for signals,
the AGC selector is usually best kept in the FAST position,
to allow the receiver gain to recover quickly after
tuning past strong signals. However, once you have a
station tuned in, SSB reception will usually be more
comfortable if you switch to the MED or even SLOW
position (keeping the receiver from picking up low-
level noise during pauses in speech). However, for CW
reception, when several signals are present in the pass-
band, the FAST or even OFF positions can avoid AGC
"pumping" (gain fluctuations) caused by strong un-
desired signals. For AM, the SLOW position is usually
better, and for 300-baud packet and RTTY/AMTOR,
the FAST or OFF positions will usually give the fewest
errors/retries.
Note: The AGC OFF position disables the over-
tection normally provided by the AGC
circuitry, If the RF gain control is left fully clock-
wise in this condition, the RF and IF amplifiers
can be easily overloaded (causing distortion)
when a strong signal is received. Correct the
overload either by setting the AGC selector to
another position, or by turning the RF control
counterclockwise to manually set receiver gain
to a comfortable level.
Noise Blanker Selection and Setting
The two noise blanker circuits in the FT-1000 are
provided for two different types of pulse noise. The NB
button activates the narrow pulse blanker, for short
pulse noise such as from switching transients, auto-
mobile ignitions and power lines. This blanker can
sometimes also reduce the level of static crashes from
electrical storms. The NB-W button activates the wide
pulse blanker, for longer duration man-made pulse
noise such as the "Woodpecker" over-the-horizon
radar. If you hear any of these types of noise, just press
either the NB or NB-W button so that the green LED above
it lights, and turn the NB control clockwise. If the
blanker seems to distort a signal you're listening to,
reduce the setting for optimum readability,