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Therefore the circuit isn't closed and no current flows, and as a result, there actually isn't any inductively coupled signal on the antenna side of the input transformer.

Then it indeed reaches the secondary winding of the input transformer, but then the function of the high impedance IF trap comes into play. We assume that via parasitic capacitance there is some IF voltage on the cathode of the first triode of the ECC85. The resonant circuit in question prevents unwanted IF signal from going backewards to the antenna through the input transformer and being radiated. That means it's a short circuit at DC and HF, and the first triode of the ECC85 is used in a grounded grid manner. The resonant circuit with C14 has a pretty high capacitance of 50 pF, so it can really only be tuned to the FM-IF frequency. First we've got to figure out how we're supposed to behave in this thread. In case Question 2 isn't up yet, I don't mind if my post gets deleted. If so, then I would like to post something on Question 2.

(Translation of text originally by Andreas Steinmetz)Īt the moment I'm not quite sure, whether we're finished with Question 1. In the 1960's, there were lengths of line strung back and forth on the back cover, which were also used for impedance transformation. Section 'b' is the whole length of the stub in the radio. The diagram doesn't exactly match our case, however. Section 'a' is the tuning stub in our case. At various times, wide aluminum foil strips were used for the antenna. The bandwidth depends mainly on the antenna. To cover a bigger frequency range, the length of the stub would have to be adjusted.ĭuring development, a tuning stub with some excess length was used, and a sliding short-circuit contact was used to determine the correct length. Since it serves as an inductance, it goes linear with omega (frequency) up to a quarter wavelength (mistake corrected). To thank the Author because you find the post helpful or well done. Matching stubs and parallel transmission lines (another thread in German on this subject) In the attached picture, the voltage (solid line) and the current (dotted line) are shown over the length of the line.Īt the terminals, the impedance is the ratio of the two. It therefore functions as an inductance, with very low loss. In the previous case and for the dipole antenna use here, this line is shorted at the end and shorter than a quarter wavelength (about 100 mm long).

If the end of the stub is either open or shorted, then the impedance at various points along the line is different (depending on frequency). Then it functions as an impedance transformer. In many configurations, the dipole is connected to one end of the tuning stub, and the lead in is connected somewhere along the line. Parallel wire conductors are used for impedance transformation or as a reactance. (Translation of text originally by Hans M.

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