Yaesu FT-847 handleiding
Handleiding
Je bekijkt pagina 38 van 108
36
FT-847 OPERATING MANUAL
RECEIVER FEATURES
RECEIVER INPUT ATTENUATOR
For situations where extremely high signal levels are
present, the receiver’s input ATTENUATOR may be acti-
vated, to reduce the sensitivity and total gain of the
receiver system.
•
To activate the receiver ATTENUA-
TOR, push the [ATT] key. The “
ATT
”
icon will become illuminated on the
display. You should also hear a de-
crease in the incoming signal
strength (and background noise)
with the ATTENUATOR on.
‚
To switch the ATTENUATOR off, press the [ATT] key
once more; the “
ATT
” icon will disappear from the
display.
AGC
(
AUTOMATIC GAIN CONTROL
)
The AGC system limits the audio output produced by
incoming signals, so as to prevent damage to your ears
and overload of the receiver components. The AGC
system works instantaneously when an incoming sig-
nal is detected, while the receiver recovery time may
be adjusted from the front panel.
When tuning around the band (look-
ing for signals), it usually is best to
have “FAST” AGC recovery time se-
lected (the [AGC-F] switch should be
pressed momentarily so that the “
AGC-
F
” icon appears at the bottom right-
hand corner of the LCD’s meter area).
In this mode, the receiver gain recovers quickly after
you tune past strong signals. Once you have a signal
tuned in, unless it is very weak, you may find recep-
tion more comfortable with “SLOW” AGC selected
(press the [AGC-F] key once more to turn off the
“
AGC-F
” icon).
RF PREAMPLIFIERS
(
INTERNAL
)
For weak-signal work, it is essential to secure the best
system Noise Figure possible. The receiver’s input
preamplifiers provide low Noise Figure for best sen-
sitivity in weak-signal situations. Individually-opti-
mized preamplifiers are provided for HF, 50 MHz, 144
MHz, and 430 MHz. In noisy locations or when very
strong signals are present, the input preamplifiers may
be switched off, thereby reducing the receiver system
gain and minimizing the chances of degraded recep-
tion due to overload or intermodulation distortion.
•
To activate the receiver preampli-
fiers, push the [RF AMP] key. The
“
RF AMP
” icon will become illu-
minated on the display. You should
also hear an increase in the incom-
ing signal strength with the pream-
plifier on.
‚
To switch the preamplifier off, press the [RF AMP]
key once more; the “
RF AMP
” icon will disappear
from the display.
RF PREAMPLIFIERS
(
EXTERNAL
)
The function of the [RF AMP] switch can be modi-
fied to allow the use of external tower-mounted pream-
plifiers on the 144 MHz and 430 MHz bands, by sup-
plying +12V DC via the ANT jack for each respective
band. If you own a preamplifier capable of accepting
its DC power via the coaxial line, you may wish to
exercise this option so as to place the preamplifier in
the line right at the antenna, where the gain and low
Noise Figure of the preamp can be used to overcome
the insertion loss of your coaxial cable feedline.
Menu #29 controls the selection for the 144 MHz band,
while Menu #30 controls the selection for the 430 MHz
band. The available choices are:
l INT: The preamplifier internal to the FT-847 will
be selected.
l EXT: The internal preamplifier will be bypassed,
and +12V DC will instead be sent up the co-
axial line for powering an external preamp.
These selections are not provided on the HF and 50
MHz antenna jacks, as there is little chance that the
system Noise Figure can be significantly improved by
mounting a preamplifier at the tower. If you wish to
use an external preamp on 50 MHz, you must supply
the necessary DC voltage via a separate power cable;
just remember not to activate the internal preamp, as
the system total gain will probably be much too high,
leading to increased probability of receiver overload
and intermodulation.
OPERATION
NOTE
The maximum allowable current drain for pow-
ering external preamplifiers is 300 mA. Check
your preamp’s specifications to ensure that this
specification is not exceeded.
Bekijk gratis de handleiding van Yaesu FT-847, stel vragen en lees de antwoorden op veelvoorkomende problemen, of gebruik onze assistent om sneller informatie in de handleiding te vinden of uitleg te krijgen over specifieke functies.
Productinformatie
| Merk | Yaesu |
| Model | FT-847 |
| Categorie | Niet gecategoriseerd |
| Taal | Nederlands |
| Grootte | 17150 MB |
