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I've set up this circuit on breadboard ( C1 being electrolytic and others disk) with Q1 as 2n3904. The simulation is perfectly fine and the oscillator works in the simulator as expected. However, the situation with the actual circuit is a bit different.

No matter what inductor L2 I choose, the frequency is always 210 KHz. I switched 47 uH with 4.7 and 10 uH; but its always 210 KHz. Even more disturbing is the fact that even if I remove some components from the circuit, ( I removed C1 and L2, not simultaneously though), and measure from L1, its still 210 KHz. To make matters worse, I just randomly waved the oscilloscope probe in air. and it still records 210 KHz ( I even put the probe on my head, and it seemed like my brain generates 210 KHz as well ! ).

So whats going wrong here ? And whats the deal with 210 KHz ?

  • \$\begingroup\$ Repeating your sim with a 2N3904 called out explicitly, I get about 250kHz. What frequency is it supposed to oscillate at? \$\endgroup\$
    – EM Fields
    Aug 31, 2014 at 22:54
  • \$\begingroup\$ Its frequency is supposed to be 1/(2*3.14*√(L2*C4) ), and therefore should vary as I change L2. \$\endgroup\$ Sep 1, 2014 at 1:10

1 Answer 1


I think your test equipment has a problem... what happens if you touch the probe with one finger and approach a power outlet (50-60HZ) with your other hand? If you still read 210KHz instead of 50-60Hz, you definitely have a test-equipment problem. Do you maybe have a "data hold" function engaged?

  • \$\begingroup\$ Will I stay alive after trying this ? \$\endgroup\$ Aug 31, 2014 at 16:55
  • 1
    \$\begingroup\$ Don't insert your finger into the power outlet, only approach it. Your body should pick up quite a strong signal from just being near the outlet. \$\endgroup\$ Aug 31, 2014 at 17:10
  • \$\begingroup\$ No. It shows 50 Hz. So I think equipment is fine. ( If my body could pickup signal from power outlet, then maybe it is picking up from ckt as well; its amplitude is 20 V.But whats up with 210 KHz. Any clue ?) \$\endgroup\$ Aug 31, 2014 at 17:27
  • \$\begingroup\$ That's an oddball frequency, but it might correlate to an electronic fluorescent ballast, if one is running in that room or a nearby room. Otherwise, it's a homing signal from the Mother Ship. 8) \$\endgroup\$ Aug 31, 2014 at 18:36
  • \$\begingroup\$ You mean to say noise ? Isnt 200 khz a bit too high for noise ? \$\endgroup\$ Aug 31, 2014 at 18:41

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