We recently posted a three-part series about using LTSpice to simulate electronic circuits (one, two, three). You might have found yourself wondering: Can you really simulate practical designs with the program? This quick analysis of [QRP Gaijin’s] minimalist regenerative receiver says “yes”.
The stated goals for the receiver design (from [Gaijins] post) are:
- Design and implement a minimalist but practically usable regenerative receiver capable of HF reception from 3-30 MHz.
- Analyze the key aspects of the receiver’s operation (e.g. behavior of the regenerative detector, gain and frequency response of the AF amplifier) using the circuit simulation tool LTspice.
- Explain the design and explaining the LTspice analysis techniques in enough detail that the interested reader can reproduce the simulation results. Also, provide several references to improved designs for regenerative detectors or regenerative receivers.
LTSpice modeled the radio’s regeneration control, the stability of the detector, and the audio amplifier. The radio built entirely out of 2N3904 transistors (and a varactor for tuning capacitance) works as expected.
We covered [QRP Gaijin’s] diary when he was building an early version of this radio. Having all of it in one place and expanded is welcome, though. This may not be the prettiest regenerative receiver we’ve covered, but it is surely the best analyzed, and it makes a great example of using LTSpice with a practical project.