Re: [IRCA] Sony SRF-59 Schematic Now Posted Online

["Steve Ratzlaff" <steveratz@xxxxxxxx>]

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
----- Original Message ----- 
From: "Paul B. Walker, Jr." <walkerbroadcasting@xxxxxxxxx>
To: "Mailing list for the International Radio Club of America" 
<irca@xxxxxxxxxxxxxxxx>
Sent: Thursday, December 27, 2007 6:41 PM
Subject: [IRCA] Sony SRF-59 Schematic Now Posted Online


> For those of you who wanted the schematic Steve said he had, I've posted 
> it
> so he wouldn't have to upload it on his dialup connection each time.
>
> http://www.walkerbroadcasting.com/srf59.jpg
> Regards,
> -- 
> Paul B. Walker, Jr.
> www.walkerbroadcasting.com
> www.wabv1590.com
> www.myspace.com/walkerbroadcasting
> _______________________________________________
> IRCA mailing list
> IRCA@xxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxxxxxx
> 

_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
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@xxxxxxxxxxxxxxxx