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Analyzing the MMR40 PTO – Spice Model


Analyzing the MMR40 PTO – Spice Model

Modeling in ltSpice:

After finding a model for the J310 Jfet Transistor at the QRPL Archives I was able to enter the model into ltspice and see that it did indeed oscillate at about the right frequency.

ltSpice model of MMR40 Hartley Oscillator

Here is the .asc file...  MMR40_Hartly_Osc.asc

As I have just started leaning ltSpice, I have not yet found a way to give the components designations with numbers that match the original circuit. For instance, I would like the jfet in this circuit to be labeled Q14, but ltSpice insists on naming it J1. So with that in mind, here is the equivalent part numbers:

Original = Spice

  • Q14 = J1
  • D1 = D2
  • L1 = L1
  • L2 = L2
  • Tickler = L3
  • R1 = R2
  • R2 = R1
  • C1 = C2
  • C6 = C5
  • C8 = C4
  • C9 = C1
  • U6 Pin 6 = R3
  • C4 = Not Shown

Other Spice Model Notes:

  1. I set the mutual inductance between L1 and L2 at 0.0 because L2 is on a toroid, and I think that would really minimize mutual coupling.
  2. I set the mutual coupling between L2 and L3 to 0.9 because they are both wound on the same toroid.
  3. I ended up setting the series Resistance for L1 and L2 to 3.5 ohms each. This is not what I calculated above, but without reducing the Q of the two coils, I was getting an unrealistic oscillation voltage of about 20vpp. By reducing the Q with the higher series resistance, the waveforms came out to match the real world circuit pretty closely.


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