One transistor can work as mixer AND oscillator – the difference signal IF will be produced in IF 1. – a second mechanically coupled L/C resonance circuit for the oscillator frequency ( OF), which is higher than the RF (difference = IF of e.g.
– ONE L/C resonance circuit for the radio frequency ( RF) – with antenna or ferrite antenna for best reception. It is rather impossible to tune 4 different L/C resonance circuits for an optimal result – but in the early radio years there were constructions like this (with radio tubes as amplifiers) – the idea of the superhet with a single-knob-tuning was born! If the reception quality is not good enough, you may use MORE tuning blocks, like in this (upper) schematic: Now you have to tune the first block, then the second, correct the first one again (fine tuning) and so on… If you will change the frequency for another station the hole procedure starts again… One way out is to use a SECOND tuning block, like in this experiment from Raytheon: But in regions with many radio stations – and in the evening, using a long wire antenna, or in the evenings in the colder seasons – it’s very difficult to “split” the sound from the stations to have a selective and sensitive reception of one station only. The Lectron tuning block can be used as ONE L/C resonance circuit. Reflex-Superhets with 2 Transistors, even with a simple IC or for Shortwave bands complete this overview.īut: how does it work? I will try to explain it with my simple words and a few samples: The most simpliest version is the 1-Transistor-Reflex-Superhet from ~ 1960.
#Af filter superhet portable
Superhets with tubes for portable radios from 193x to 195x can also be built with Lectron, see here and here. Even the inventor of Lectron had plans in 1966 to develop blocks, see here. In this forum we had several topics with the introduction of AM receivers with this principle. The common superhet(erodyne) receivers came up in the 1930ies (with radio tubes), and since November 1954 we have the transistorized superhets in pocket radios.
0 kommentar(er)
