Asymod IIIs, Installation Manual

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Basic Installation with Bias Modification
Fig 11. Galaxy DX 44 single final AM/FM Transceiver
Figure 11 shows a perfect example of a Class C biased RF final stage. L35 and L47 pull the bases of TR43
and TR44 far down and the Q-point is set some way below the cut-off point in the DC load line. As a
result the transistors will start conducting only after the input signal amplitude has risen above the base
emitter voltage (Vbe~0.7V).
To modify the bias on any multimode transceiver, RF chokes such as L35 and L47 above must be
employed. Typically a 22uH inductor from the bases to ground will do. Simply remove the RF chokes on
the multimode transceivers providing the present bias and connect them to ground in the same manner
as L35 and L47 in the Galaxy DX 44 as seen on Fig 11.
In the case where -100% modulation cannot be achieved in any one of the Advanced Installations for
multimode transceivers presented in this manual, 99.9% of the time will be a bias issue. In such case, the
bias has to be adjusted to the lowest level, and, if this is not sufficient, then the method depicted on Fig.
11 has to be employed. To avoid having to adjust the bias and keep all modes with their corresponding
bias levels, a relay or switch has to be employed for the bias section, as seen on the Advanced and
Ultimate Installations with Bias Modification starting on page 28. This will allow to switch from the
normal, factory bias configuration to Class C bias when in AM mode using the 22uH inductors seen in fig
12.