Accessory Installation; Linear Amplifier Interfacing - Yaesu FT-920 Operating Manual

1. Linear Amplifier Interfacing

The FT-920 can be used with the (optional) Yaesu
FL-7000 Linear Amplifier, which provides automatic
band switching through the use of digital data sent
via the B jack on the rear panel of the transceiver.
AND
Most other commonly-used linear amplifiers may also
be used with the FT-920, so long as the Tx/Rx switch-
ing voltages and timing (sequencing) for the
amplifier's control relay(s) are not extraordinary.
Tx/Rx Control Devices
for Linear Amplifier Switching
Two control devices are provided in the FT-920 for
Tx/Rx control of an linear amplifier's relay(s).
 An open-collector transistor switch provides a
solid-state, fast-acting closure to ground for
low-voltage/low-current situations; maximum
ratings are +50 V DC at 500 mA (maximum
dissipation of 25W), and relays using negative
DC voltages or AC of any kind must not be
used with the transistor switch.
The transistor switch's "hot" lead is identified
as T G (since it closes to "G
X ND
and is provided on Pin 2 of the B
nector on the rear panel of the FT-920. It is
also provided via the rear-panel T
when the T -R switch is set to the T
R Y
tion.
‚ A mechanical relay is provided for high volt-
age/high-current applications, although the
relay will not be fast enough for QSK (full break-
in) CW operation; maximum ratings for the re-
lay contacts are 220 V DC (maximum) at 270
mA, 30V DC at 2 A, or 125 V AC (maximum
AC voltage) at 500 mA (60 Watts total maxi-
mum dissipation).
The relay's contacts may be accessed by con-
necting a shielded cable to the rear-panel T
G jack.
ND
If the relay is being used, the T
jacent to the T G
X ND
the R position; conversely, if you are using
Y
the transistor switch, leave the T
the T position, so as to eliminate the clicking
R
of the relay.
FT-920 Operating Manual
" on "T "),
ND X
(DIN) con-
AND
G jack
X ND
posi-
R
X
-R switch ad-
R Y
RCA jack must be set to
-R switch in
R Y
The relay provides a mechanical closure to Ground
on Transmit, while the (NPN) transistor switch sinks
its (open) collector to Ground on Transmit. Check
with the manufacturer of your amplifier (or other de-
vice) to confirm the amplifier switching voltage and
current, if they are not clearly stipulated in the docu-
mentation for your equipment.
þ Be absolutely certain to check the position of the
T -R switch prior to connecting any external de-
R Y
vice to the T G jack. Never connect an AC
X ND
voltage, or a negative DC voltage, to the T
jack if the T -R switch is set to T
R Y
Warranty on this product does not cover damage
caused by improper connections (excessive or im-
proper voltage) to the rear panel jacks of the FT-
920.
About ALC
The FT-920 provides an external ALC jack on the
rear panel (RCA-type jack) for input of Automatic
Level Control voltage from a linear amplifier.
ALC voltage is used to provide dynamic control of
the output of the transceiver, so as not to provide
more drive than is needed for full amplifier output.
The ALC control voltage range is 0 to -4 V DC, with
the voltage going more negative as the amplifier's
drive requirements are approaching fulfillment.
The FT-920's ALC system is very typical of designs
in the amateur radio industry, and consequently is
compatible with many manufactured and home-built
amplifiers. However, ALC voltage may be generated
by an amplifier in a manner incompatible with effi-
cient ALC operation in the FT-920, and it is important
that you recognize the differences in amplifier ALC
circuits before proceeding with ALC line connection.
r ALC circuits which detect Power Output from
the amplifier, and generate negative-going ALC
control voltage when maximum output power
has been realized, will generally work properly
with the FT-920. The exact amount of ALC volt-
age fed to the FT-920 can usually be adjusted
via a potentiometer on the rear panel of the
amplifier.
r ALC circuits which detect Amplifier Tube Grid
Current , and generate ALC voltage when ex-
cessive grid current is present, may not work
well with the FT-920 and other similar trans-
G
X ND
. The Limited
R
13