Re: Connecting Sony SRF-XX to outdoor antenna for improved FM reception?


Bruce Carter
 

I would like to connect my Sony SRF-86 to the home external antenna to improve FM reception.
Sony has two types of walkman radios. One based on conventional superhet architecture, and the other based on their proprietary CXA1129 IC. The conventional superhet is very prone to overload. The CXA1129 based not nearly so much so. From the looks of the SRF-86, I can see you might be lucky and have a CXA1129 model. If so - it is like the SRF-59 and a little DX machine in a very reasonable package! The CXA1129 IC has a bit of RF gain, something not usually found in a two gang tuner, and the equivalent of three ceramic filter IF - where most only have one. So - it has potential.

Radio - It looks like the 3.5mm TRS jack sleeve (outer ring) is the ground and can be used for an external antenna
http://www.fixup.net/tips/srfs83/srfs83.htm
Yes, you are correct, the outer ring is the antenna. Also note that the SRF-83 referenced in the article is a CXA1129 based unit, and therefore able to handle the added signal from an external antenna.

I wouldn't worry so much about matching and baluns -

Your "real" FM antenna input is on the far side of a wide band ceramic filter. That is how they do the frequency separation of audio headphone return and antenna RF. But those wideband FM ceramic filters are LOSSY - you can probably soup up your walkman just by removing that wideband filter, and running a separate wire directly to the tuning capacitor side of the ceramic filter. The connections should be very obvious - the ceramic filter has three leads. One goes to the headphone return, the middle is ground, and the third is RF input - which goes to a local / DX switch. Open the switch, there is no antenna connection. Close it - DX - and the antenna is connected. Cheap and very dirty -

A bit of a warning, if this is a conventional superhet set, running antenna directly in after removing the wideband filter will overload the ____ out of the thing. You probably want to check before soldering. CXA1129 - worth the effort. Conventional - go down to Walmart and pay $15 for an SRF-59 because I guarantee it has the sensitivity you need.

Next connection for an external antenna - find a real ground somewhere in the radio. Metal can case, etc. That should go to the shield of antenna coax, center conductor to where the wideband ceramic filter was. From what I can tell, a CXA1129 based walkman would handle the modifications well and DX like crazy!

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