Group: I will leave the SRF 59 Diagram posted online for an indefinate amount of time, so feel free to download the jpg image or share the URL with friends.
http://www.walkerbroadcasting.com/srf59.jpg Paul Walker On Dec 28, 2007 12:34 AM, Steve Ratzlaff <[EMAIL PROTECTED]> wrote: > Thanks to Paul for putting my handdrawn diagram on his webpage. I presume > that the several of you who asked for the diagram in the past several > hours > have obtained it from Paul's site. > I should note that the diagram is probably not 100% accurate. Several > traces > I was unable to figure where they went on the IC1. The sections associated > with the tuning cap are all using the +1.5 volts supply as the common > reference, not the minus/ground. This is probably to supply voltage to > some > of the IC1 pins thru external circuitry. You'll notice that in the FM > tuning > section, L1/C1 and the associated tuning cap section don't go anywhere. > Since I couldn't tell where pin 29 on IC1 went, it probably goes to the > junction of C2/L1, for the FM input tuning. Since every other pin on IC1 > is > used, pin 29 is probably also used. > The ferrite loopstick connections aren't verified either, just guessed at. > I'd have to remove the loopstick and trace out the two windings to be sure > where they really go. The AM tuning section doesn't really look functional > as drawn, and no doubt is not correct. > I have another SRF-59 on order and will do some component dissassembly > after > I receive a backup radio. > Someone asked how to hook up an external digital dial to the AM section, > to > be able to determine what tuned frequency is dialed in. That would have to > be done as a new experiment; I have no real idea if the dial could be > added. > If the radio in fact has an approximate +57kHz offset from the input-tuned > frequency, then if the digital dial could be offset that small amount, and > be coupled to the AM local oscillator such that it does not detune the > oscillator, then perhaps the digital dial might work. > I found touching the tuning cap section associated with L3/C5 detuned the > AM > section, so that would be a good place to start with trying a digital dial > connection, with some type of low capacitance isolation buffer stage. > For what I observed using the spectrum analyzer, with the two presumed > local > oscillator RF signals in AM mode, with the lowest one about +57 kHz higher > than the input frequency, it's possible that what I thought was the second > harmonic is really the signal that IC1 is using as the local oscillator, > and > that the lower one is some type of sub harmonic. But all DSP ICs I'm aware > of require the input signals to be well below 100 kHz, and using the > second > harmonic as the actual local oscillator doesn't seem to fit that > requirement, where possibly the +57 kHz signal just might. > An experiment could be done to remove the AM oscillator signal and inject > an > external one from a signal generator and try to figure out what local > oscillator frequency is really used by the radio. > It seems to me since the radio is not shielded, that if the local > oscillator > is really just +57 kHz higher than the input, then a strong local BCB > station would eventually fall on the local oscillator signal's frequency > and > mess up the radio reception. So far no one has reported anything like that > being noticed. > I hope to do some experiments once I have another backup radio. > One might think that if Sony can sell a radio for $15 including free > shipping, and still make a profit, that this particular circuit might be > used in other Sony miniature radios, to get the costs of integrated > circuits > and such way down. > > I have been tracing out circuits for fun for many years--I do it for > enjoyment and to learn how other designers do things. This little circuit > board actually was not that hard to get the basic circuit figured out, > with > the limitations noted above for parts that need to be removed to figure > out > some more details. There's got to be some amazing things going on inside > IC1 > to take a radio signal in and put out demodulated audio for both AM and > FM, > with no external parts except the presumed-FM stereo multiplex > transformer, > and external components for the local oscillators. > > Best regards, > Steve > _______________________________________________ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
