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2 transistor Butler Oscillators

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  • zl1ujg
    Hi, Name is Kevin, ZL1UJG. New to the reflector and new to SDR. I have used the 2 transistor Butler oscillator many times. (VHF/UHF/microwave) What can occur
    Message 1 of 1 , Dec 29, 2007
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      Hi,
      Name is Kevin, ZL1UJG. New to the reflector and new to SDR.

      I have used the 2 transistor Butler oscillator many times.
      (VHF/UHF/microwave) What can occur when the transistors have more than
      sufficient loop gain, during the RF cycle, is that they are partially
      cut off. This can be measured by looking at the Vbe of the transistors
      in the oscillator.(using a DVM isolated with a 10k resistor and
      measuring Vbase and then Vemitter of the transistors) With some modern
      SMD devices I have measured 0.15V Vbe. I have not got any of the kits
      mentioned on the reflector yet, so cannot measure what these units are
      like. Adding clamp diodes across the tuned circuit (such as 1N4148)
      typically brings the Vbe back to a suitable range.

      Another point with oscillators is the effect that PSU noise has on
      phase noise. (78 and 317 type regulators can increase the composite
      phase and amplitude noise (especially seen when the frequency is
      multiplied up.
      The Wenzel site (www.wenzel.com) has active PSU filter designs which
      can be added to the output of the regulators to reduce the noise.

      Kevin
      ZL1UJG
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