You probably thought the topic was relays? Nope...just trying to keep this section alive. I just got XP-Pro recently and I guess this is why I can finally post a schematic. I guess the size must be limited to something like 307kb but never worked before. Anyway here's a good one. There was a bit of discussion on oscillators a while back and I mentioned that none of the posts had a hartley oscillator. I have done a good bit of work with oscillators and found the Hartley to be superior in many ways to all other types of oscillators.
1. They run cool (heat is enemy of oscillator and can generate phase noise)
2. Best free running VFO (variable freq osc)
3. Low power consuption
4. Wide range of tuning (most PLLs uses Colpitts which is silly because the two varactors in the tank circuit divide their tuning range in half)

This example uses a JFET and is actually configured as a VCO (voltage controlled osc). If you remove the "error dc" input which would be the output of a loop filter in a PLL and remove the varacter then you have a pure free running osc whoes freq is detemined primarily by L7 and C19 tank circuit.
Posted on 2004-07-13 19:45:55 by mrgone