Low- Distortion Class-A Operation - Yaesu FTDX-9000D Operation Manual

SSB/AM M
Class-A operation of the FT
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 se-
lected.
Engaging the "Class-A" mode
actually places the transceiver
in a condition whereby the Bias
level may be adjusted, 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.
Advice
H During Class-A operation, ten Amps of Bias current will be flowing, regardless of the modu-
lation 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). Depending on the temperature, you may wish to
reduce the setting of the BIAS control, so as to reduce the amount of heat being generated.
H Because you can monitor the heat sink temperature on the TFT, you can always be aware of a rise in temperature during
Class-A operation. Normally, the temperature is below 80°C; if it rises to near or above this value, however, we
recommend you adjust the BIAS control toward Class AB (more to the left) so as to reduce the heat being dissipated.
H 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.
Page 90
T
L - D
9000D transmitter is provided, yielding ultra-low distortion products during SSB operation.
Continuous adjustment of the
Bias Level between Class-A
and Class-AB is possible.
Class-AB
Class-AB and Class-A Operating Principle
(L - D
CLASS-A O
Class-A
FT 9000D O
CLASS-A O
CLASS-A switch
BIAS knob
Input
M
)