Low- Distortion Class-A Operation - Yaesu FT DX 9000 CONTEST Operation Manual

SSB/AM M SSB/AM M SSB/AM M
SSB/AM M SSB/AM M
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Class-A operation of the FT
operation. Power output during Class-A operation is 75 Watts.
To engage Class-A operation, press the [ CLASS-A ]
switch. The imbedded Red LED will light up, confirming
that Class-A operation has been selected.
Engaging the "Class-A" mode actually places the trans-
ceiver in a condition whereby the Bias level may be ad-
justed, using the [ BIAS ] control, to set the transceiver for
operation anywhere between Class A and Class AB (which
has lower heat dissipation but higher distortion products).
Clockwise rotation of the [ BIAS ] control increases the
Bias, and fully clockwise rotation of the [ BIAS ] control
will place the transmitter in fully Class-A operation.
Counter-clockwise rotation of the [ BIAS ] control will
move the transmitter toward Class AB operation.
To exit from the CLASS-A mode, press the [ CLASS-A ]
switch once more. The Red LED imbedded in the switch
will go out, confirming that the CLASS-A mode has been
disengaged.
During Class-A operation, ten Amps of Bias current will be flowing, regardless of the modulation level that
leads to actual power output. Therefore, if the ambient temperature in your operation location is high, the
transceiver temperature may rise as well, due to the high bias level (which must be dissipated as heat). Depend-
ing on the temperature, you may wish to reduce the setting of the [ BIAS ] control, so as to reduce the amount of
heat being generated.
During Class A operation, we recommend that you monitor the heat sink temperature by pressing the [ TEMP ]
switch so as to engage the temperature monitoring mode of the [ TEMP/SWR ] meter. Usually, the temperature
will be well below the 80 °C "Red Zone," because the fan speed will increase to control a rise in temperature. If
you are operating in a hot environment, though, and the increasing fan speed does not maintain the temperature
below 80 °C, try adjusting the Bias Level temporarily in the direction of Class AB operation; this will reduce the
amount of heat being dissipated in the heat sink.
The Bias Level is displayed on the [ VDD/BIAS ] meter when the [ BIAS ] switch is pushed. On the "Bias" scale,
"0%" represents Class AB operation, while "100%" represents Class A operation.
An innovative aspect of the "Class-A" mode is that the actual power output is always limited to 75 Watts. So
even though you might adjust the [ BIAS ] control in the direction of Class-AB operation, the power output will
not rise; this eliminates the need, for example, to re-tune your linear amplifier, if used.
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- D
OW ISTORTION
9000 Contest transmitter is provided, yielding ultra-low distortion products during SSB
DX
[ BIAS ] Knob
- D - D - D - D - D CLASS-A O CLASS-A O CLASS-A O
CLASS-A O CLASS-A O
IST IST IST IST ISTOR OR OR OR ORTION TION TION TION
TION
CLASS-A O
PERATION
[ CLASS-A ] Switch
A
DVICE
FT 9000 C
DX
)
PERA PERATION PERA TION TION TION
PERA PERA TION
[ VDD/BIAS ] Meter
[ TEMP/SWR ] Meter
VDD BIAS TEMP SWR
[ BIAS ] Switch
O M
ONTEST PERATION ANUAL