These video’s are made for beginners and all people interested in this matter. In this video you see the great importance of the correct voltage on the base, given a certain application of the transistor (working area/working point/transistor characteristic). A transistor acts different according to the voltage on the base. You can set the transistor for instance in the non-lineair part of the characteristic. In that case the transistor does not act purely as amplifier, but is usable as mixer for high frequency stages. The oscillator signal can be inserted on the emitter or the base of the (bipolar) transistor via a capacitor (frequency dependent). High frequency mixing is a critical process, the energy of the HF (antenne/first HF stage) signal and the oscillator signal should be carefully balanced. The values of the coupling capacitors (from HF signal/antenne and from oscillator signal) are the keys to succes. For instance 50 P - 470 P for Shortwave 2-15 mhz. The schematic is usable as simple mixing stage in a shortwave radio, with some shortcome in mixing very strong antenna/HF stage signals. But in general this is a good way to design a mixer for a Shortwave radio. Connect the oscilloscope (vert. entrance) to the secondary coil of the IF transformer, connect oscillator (E or B) and HF stage (B) (via capacitor 50P-470P) and vary the voltage on the base of the transistor till the mixer works properly. More about the transistor in grounded emitter figuration in my book “Schematics 1″, info video on my channel (website Lulu).
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hahahaha nen hollander die engels spreekt xD