Vhf/Uhf Preamplifiers - Yaesu FT-847 Operating Manual

Hf + v-uhf all mode transceiver
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VHF/UHF Preamplifiers

For maximum improvement of system noise figure,
VHF and (especially) UHF preamplifiers should be
located as close to the antenna feedpoint as possible.
This puts the preamplifier's low-noise-figure gain
ahead of the loss in the coaxial cable feedline.
The FT-847 provides the capability to deliver +12V
DC at up to 300 mA via the 144 MHz and/or 430 MHz
antenna jacks, for those preamplifiers equipped to re-
ceive DC power via the coaxial cable. Menu items #29
and #30 provide the following operational settings:
l In the "INT" mode, the internal preamplifier of
the FT-847 is used, and no DC power is deliv-
ered to the rear panel antenna jack(s).
l In the "ANT" mode, the internal preamplifier is
bypassed, and +12V DC is delivered to the an-
tenna jack(s).
Menu #29 controls the setting for the 144 MHz an-
tenna jack, while Menu #30 controls the setting for
the 430 MHz antenna jack. These settings are totally
independent, so each antenna port may be set for the
configuration you desire on that particular band.
If you wish to use both the internal preamplifier and a
very-low-noise tower-mounted preamp, set Menu #29
and/or #30 to "INT" and supply DC power to your
preamp(s) via a separate DC cable.
FT-847 O
PERATING
A
CCESSORY
M
ANUAL
I
NTERFACING
Caution!
Check your antenna system switching carefully
before activating the "ANT" setting of Menu #29
or #30. If there are any antennas in your system
which present a DC Ground when checked with
an Ohmmeter, you should be certain that there
is no way that such an antenna can be connected
directly to the FT-847 (without the intervening
preamplifier). Direct connection of a DC short
to ground will instantly destroy the transistor
passing the +12V DC to the antenna jack.
This trouble may be avoided by putting your
antenna switch(es) in a remote position on the
antenna side of the preamplifier, so that all an-
tennas are isolated from the FT-847 by the
preamp(s).
The Limited Warranty for the FT-847 does not
cover damage caused by improper installation.
Check your antennas before connecting them
to be sure!
Note: the default selection for both Menu #29
and #30 is set to "INT" at the factory to avoid
accidental damage to your transceiver.
Installation
15

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