@ Michael:

    there are about 17 different methods (digital radio, s. Wikipedia) worldwide in test – so I am tired since a couple of years to read or work with. Please wake me up when all technical problems are solved and the overall availability is garanteed! And how all the “old” (billions of) radios should be gathered and recycled! It’s an absolutely overkill to receive and prepare a radio station signal to listen to – when it takes hundred thousands (or millions) of transistor systems for processing. Why should I purchace and use a medium sized computing center and support programmer teams to code the logic, and wasting energy (voltage/current !) when it’s possible with one or two transistors like Lectron block #2461 ? We only have one planet to live on…

    @ Frank:

    The IF frequency was (and may be) on any frequency outside of the normal radio bands, e.g. 50…150 | LW | 300…500 kHz/kc. BUT: meanwhile (within the last 50…70 years) several frequency ranges are reserved for time signal (e.g. DCF 77.5 kHz/kc), weather, nautic (radio signals instead or additional to lighthouses at the coasts, think on the BRAUN T1000 station receiver with compass and two ferrit antennas for locating: 90 degrees crossed) on LW (long wave band). Strong LW stations like RTL may cause mixed radio signal products (second harmonic waves, together with special weather phenomena) so that since ~ 1954 the range 455…485 kHz was reserved for AM IF – the oscillator works like a transmitter, so it had to be on a frequency without near any radio station. It is possible to use ceramic filters (piezo resonators) in the IF amplifiers – all of these have an embossed or stamped number = IF frequency (on this photo the marking is sometimes on the unvisible topside):

    American and Japanese radios all uses 455 kHz/kc – a far as I can remember.

    The FM IF frequency started in Germany (and Europe?) with 6.75 MHz/mc, changed around 1960 to the – international – standard of 10.7 MHz/mc.

    It’s no problem to use only one transistor for both IF frequencies, see this example of a pocket radio:

    The collector is first connected with the FM IF coil, followed by the AM IF coil via tap. the FM coil inductivity is very low and is no remarkable influence for the AM coil.  The alignment should start with the FM part (all standard filters to highest noise between two stations, the two ratio filters at the end: symmetrical curve), then the AM part.

    I had until now no deviations of the capacities – may be the warmth in TVs caused the drift – warmth always is a “good” way for premature aging…


    • This reply was modified 3 years, 5 months ago by Guenther.
    • This reply was modified 3 years, 5 months ago by Guenther.