28-06-2020, 03:06 PM
Trial and error and experimenting is fine and brilliant once you know how something is meant to be used.
Simulation is very tricky and you need to know what the parts really are, not just the values on them. Inductors, transformers and active devices other than op-amps are tricky to hard. Simulation doesn't design anything. It's a useful tool for complex and/or expensive to build designs. Also for things like inverters, SMPSUs, complex filters etc where you absolutely know the real resistances, coupling, capacitances, core properties etc of inductors or transformers. If you were expert enough to simulate a superhet properly you likely wouldn't need to unless going into volume production. It's very valuable for production designs that already work on the bench to see the effects of component tolerances, e.g. Monte Carlo simulations. But the model needs to take account of all the real world resistances, inductances and capacitances of parts that are not simple resistors or near perfect capacitors.
When it comes to an active device it's not hard to get it to oscillate and nearly any active device works as mixer. Those are the two most critical aspects of a superhet, so it makes sense to start with the best known design for the kind of active device you are using: Pentode, Heptode, Triode-Hexode, Bipolar transistor or dual gate FET. some devices such as a ring diode mixer, Pentode, Hexode, Dual Gate FET or dual g1 Rod Pentode are inherently only sensible as a mixer if using a separate oscillator.
Also if building your own superhet a separate mixer and oscillator is ALWAYS better. A Triode-Hexode, though a single envelope, is really a separate mixer and oscillator. A Heptode or Octode is really a sort of triode and pentode or hexode IN SERIES, and thus is really really inferior to the Triode-Hexode (or Triode Pentode) in even the same circuit. Note any Triode-Hexode circuit works fine with a separate Pentode (LO into g2) and Triode oscillator (or Triodised pentode). A single Pentode , triode or bipolar transistor as a combined mixer oscillator is cheap but terrible performance. At the VHF a single triode (or triodized Pentode), transistor or FET was often used simply because of the cost and difficulty of a separate mixer and oscillator. Almost professional gear from the 1980s onward used separate mixers and oscillators. It's now standard in all VHF, UHF and higher gear other than cheap domestic radios.
Simulation is very tricky and you need to know what the parts really are, not just the values on them. Inductors, transformers and active devices other than op-amps are tricky to hard. Simulation doesn't design anything. It's a useful tool for complex and/or expensive to build designs. Also for things like inverters, SMPSUs, complex filters etc where you absolutely know the real resistances, coupling, capacitances, core properties etc of inductors or transformers. If you were expert enough to simulate a superhet properly you likely wouldn't need to unless going into volume production. It's very valuable for production designs that already work on the bench to see the effects of component tolerances, e.g. Monte Carlo simulations. But the model needs to take account of all the real world resistances, inductances and capacitances of parts that are not simple resistors or near perfect capacitors.
When it comes to an active device it's not hard to get it to oscillate and nearly any active device works as mixer. Those are the two most critical aspects of a superhet, so it makes sense to start with the best known design for the kind of active device you are using: Pentode, Heptode, Triode-Hexode, Bipolar transistor or dual gate FET. some devices such as a ring diode mixer, Pentode, Hexode, Dual Gate FET or dual g1 Rod Pentode are inherently only sensible as a mixer if using a separate oscillator.
Also if building your own superhet a separate mixer and oscillator is ALWAYS better. A Triode-Hexode, though a single envelope, is really a separate mixer and oscillator. A Heptode or Octode is really a sort of triode and pentode or hexode IN SERIES, and thus is really really inferior to the Triode-Hexode (or Triode Pentode) in even the same circuit. Note any Triode-Hexode circuit works fine with a separate Pentode (LO into g2) and Triode oscillator (or Triodised pentode). A single Pentode , triode or bipolar transistor as a combined mixer oscillator is cheap but terrible performance. At the VHF a single triode (or triodized Pentode), transistor or FET was often used simply because of the cost and difficulty of a separate mixer and oscillator. Almost professional gear from the 1980s onward used separate mixers and oscillators. It's now standard in all VHF, UHF and higher gear other than cheap domestic radios.
