Hey,
I've been trying to get a feel for building LC oscillators (Colpitts) since i have a school project which will require me to build a couple. Unfortunately the only transistors i have access to at home are some BC547/548 general purpose transistors. So i took to the web and found a number of transmitters using these transistors supposedly capable of operating around the commercial FM band.
I've tried to simulate the oscillators from these circuits using BC547/548 models and have had trouble getting them to oscillate. Originally i was attempting to physically build an oscillator to oscillate around the 10MHz (thinking the transistor would work okay at this frequency) mark with no success, so i decided to simulate and found that it wouldn't work there either. I found replacing the BC547/548 transistor with a generic NPN spice model or even a 5GHz wideband transistor would get it to oscillate in the simulations. Another thing that made the circuits oscillate in simulations was to use a large inductor (say 100uH instead of 0.5uH, but from a practical point of view I want to keep the inductor small)
So, just wondering, is it possible to build a colpitts oscillator using a BC547/548 at a frequency of 10MHz. Im actually using a breadboard for construction (I know parasitics), but at 10MHz i've been told i should be able to get something regardless of parasitics.
I've been trying to get a feel for building LC oscillators (Colpitts) since i have a school project which will require me to build a couple. Unfortunately the only transistors i have access to at home are some BC547/548 general purpose transistors. So i took to the web and found a number of transmitters using these transistors supposedly capable of operating around the commercial FM band.
I've tried to simulate the oscillators from these circuits using BC547/548 models and have had trouble getting them to oscillate. Originally i was attempting to physically build an oscillator to oscillate around the 10MHz (thinking the transistor would work okay at this frequency) mark with no success, so i decided to simulate and found that it wouldn't work there either. I found replacing the BC547/548 transistor with a generic NPN spice model or even a 5GHz wideband transistor would get it to oscillate in the simulations. Another thing that made the circuits oscillate in simulations was to use a large inductor (say 100uH instead of 0.5uH, but from a practical point of view I want to keep the inductor small)
So, just wondering, is it possible to build a colpitts oscillator using a BC547/548 at a frequency of 10MHz. Im actually using a breadboard for construction (I know parasitics), but at 10MHz i've been told i should be able to get something regardless of parasitics.