Re: [IRCA] Vast selectivity improvement for my SRF-M37V

["Mike Westfall, Lost Almost NM" <mwdx@xxxxxxxxxx>]

If it's for a 450 kHz IF, go ahead and try it if it's not too big.
The one I used was the same size as a modern Murata CFULA series ceramic filter.




On Jan 2, 2008 3:29 PM, Gil Stacy <gilstacy@xxxxxxxxx> wrote:
> Mike,
> That's good news.  I have a spare Kiwa 6.2 kHz filter for my FRG-7.  Any
> reason not to use it??
> 73, Gil
>
>
>
> On 1/2/08, Mike Westfall, Lost Almost NM <mwdx@xxxxxxxxxx> wrote:
> >
> > This is for you experimenters out there that are complaining about the
> > poor selectivity of the Sony SRF-M37V Walkman mighty-mite ultralight.
> >
> > It turns out that the SRF-M37V does not use the same chip as the
> > SRF-59. I don't know where I ever got the idea that it did.
> > I took my SRF-M37V apart and there is a TA737A5 at its heart. Of
> > course, I couldn't find a datasheet anywhere for it. I guess it's a
> > Toshiba part, though.
> >
> > Anyway, there is a small 450 kHz ceramic filter on the circuit card
> > next to the main chip, which I unsoldered and replaced with a SFP450I
> > ceramic filter from a dead DX-440 that I had laying around.
> >
> > The results were simply staggering! I can now receive the very weak
> > KABR on 1500 kHz, despite the fact that my local KRSN is right next
> > door on 1490!  Impossible to do on my car radio, even!.
> >
> > For even more selectivity, I might have tried to use the narrower
> > SFR450K from the same DX-440, but it's a little bigger, and wasn't
> > sure it would fit, but the filter I used gives great selectivity.
> >
> > Taking the radio apart isn't too hard. After removing the four screws,
> > the case pops right apart, without using fingernails, etc. There are
> > two circuit boards inside, one for the keyboard/microcontroller, and
> > the other for all the analog stuff. Yoiu have to unsolder on red wire
> > to get the two to unfold from each other. Then you have to unsolder a
> > couple spots on a copper foil shield which is covering the TA737A5 in
> > order to get to the solder pads for the ceramic filter, which is
> > marked "50J". Remove the the filter and clean out the holes. The new
> > filter has to be laid on its side, and small wires run from it's pins
> > to the holes where the old fiter was  (no, it's not a drop-in
> > replacement!). AFter you fold the two circuit boards back together,
> > it's in there nice and cozy, and won;t be going anywhere. If you're
> > worried about movement weakening and breaking your wires, I guess you
> > could dab some RTV under the new filter to hold it in place, but I saw
> > no need for that.
> >
> >
> > NOW I have a sensitive, selective little DX monster that can switch to
> > 9kHz tuning!
> > I can't wait to try it with my RS Loop later!
> >
> > --
> > Mesa Mike
> > LA de NM
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-- 
Mesa Mike
LA de NM
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