[IRCA] Ultralight Technical: The SRF 59 mysteries revealed at last

["Steve Ratzlaff" <steveratz@xxxxxxxx>]

I've been asking around about any technical information on the SRF 59, 
specifically the Sony CXA1129N integrated circuit that forms the heart of 
the receiver. I finally ran across one person, Robert Culter, who has been 
interested in the SRF 59 and the Sony IC for some time and has been able to 
gather quite a lot of information about it. Bob has given me permission to 
include his remarks, and I'm simply posting his complete email, with an 
additional postscript at the end. If you have a technical bent and have been 
interested in the electrical workings of the SRF 59, this should answer a 
lot of questions. Nick Hall-Patch, being an IEEE member, has obtained a copy 
of the paper referenced in Bob's remarks, and Nick will probably eventually 
have more to say about this Sony IC and its use in the SRF 59.

Best regards,
Steve
NE Oregon

Hi Everyone,       (January 4, 2008)

The Sony SRF59 is indeed a very interesting receiver.  The operation of the 
CXA1129N chip (FM/AM) is described in great detail complete with section 
schematics in an IEEE paper:

 Advanced Low Voltage Single Chip Radio IC

 By Okanobu, Tomiyama, and Arimoto

 IEEE Transactions on Consumer Electronics, Vol. 38, No. 3, August 1992, pp. 
465-475

If you can find this article in a technical library, it is worth the search. 
It can also be purchased through the IEEE Explore website (which I had to do 
eventually after I copied the article in a technical library, threw it away 
during a massive cleanup, and then discovered the SRF59 and just about went 
nuts trying to find the article again).  The IEEE is quite serious about 
copyright, so I don't feel free to distribute the article without 
permission.  There are a number of other Sony IEEE articles on sub-1V 
receiver ICs but this article seems to describe the CXA1129N chip directly.

The CXA1129N chip has no published data sheet, either in English or in 
Japanese (I have looked everywhere).  Sony does not sell the chip to other 
manufacturers in spite of the alleged stock by some Chinese websites.  The 
above article mentions an AM-only version that was used in card-type 
receivers sold only in Japan.  The CXA1129N is a phasing type IC but is not 
direct conversion.  The FM IF frequency is 150 kHz and the AM IF frequency 
is 55 kHz.  The phasing mixers (used for both bands) are driven by an LO 
that is divided by 2 to obtain quadrature outputs.  Both mixer outputs are 
sent through 4th order active phase shift networks that maintains 90 degrees 
difference within 1 degree over the entire IF range of 50-250 kHz for both 
AM and FM. The AM section has three 2nd order biquad 55 kHz band pass 
filters (to replace external ceramic filters) and achieves an adjacent 
channel rejection of 35 dB.  The chip will work down to 0.95VDC.  The FM 
design seems similar to the Philips TDA7000, but the AM section is unique. 
Toshiba also has a 1-volt AM radio chip, but it has conventional operation.

I very much appreciate the link to the SRF-PSY03 service manual.  The 
circuit board does look identical to the SRF-59 that I have.  There is a 
website discussing the various Sony receivers including the SRF-59 and also 
shows modifications for lower bass response: 
http://www.fixup.net/tips/srf49/srf49.htm .  The SRF49 and SRF83 use the 
same CXA1129N chip.

I have considered modifying an SRF59 for shortwave operation but do not know 
how high the chip will tune (no data sheet).  The only way to get a chip is 
to take apart or modify one of the Sony radios.

73, Bob   N7FKI

(There appears to be a US Patent, 5020147, on the CXA1129.  The patent does 
not have the partial schematics of the filter and delay circuits, so the 
IEEE article is still the best reference.)

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