L2 performs as an RF choke,providing a supply current to T2 through L3 but blocking the RF signals.
As far as signals are concerned L2 can therefore be considered an open circuit and be neglected.
T3 is a common collector amplifier enabling the connection of loads to the generator without affecting the performance.
The input impedance of T3 is high but is paralleled with R13 and R14 that lower the total impedance connected to pin 3 of L3 somewhat.
A high impedance connected to the tank circuit allows higher Q figures and therefore better performance of the oscillator.
The experimental study of this circuit can be carried out as already described for the Hartley oscillator.
Voltages and singnals at various points of the circuit should be inspected,recorded and explained for the purpose of understanding each aspect of the circuit operation.
The second part of the exercise consists in operating the Colpitts oscillator as an AM modulator.
Refer to Fig. 8A and 8B.
The BP filter of the B4110 board has,once again,to be configured as an LF oscillator to provide a test-modulating signal to the "MOD IN" input of the Colpitts oscillator.