variable HF oscillator

53 1 variable HF oscillator of amplification needs to be empiri- cally established, so that amplifi- cation is at a maximum without affecting stability. The complete circuit diagram is shown in figure 2. Since operation has already been explained by the block diagram, this figure should be easy enough to follow. The Colpitts oscillator is built around T1, the buffer/amplifier with T2 and T3 and a 741 (IC1) is used as a control amplifier. R. Van den Brink Editorial Note The author presented this design as an idea "on paper" which is why the practical elaboration is not perfect. Thus, the 10 x amplifier (T3) has a limited bandwidth thereby giving rise to possible distortion. Furthermore, decoupling the source from T1 limits the modulation bandwidth and the AGC is derived from the output, so that you have to be careful what you connect to the output. Since real HF experts will succeed in getting the circuit to function well up to at least 10 MHz with 1 kHz modulation, the idea was co...