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

["Gil Stacy" <gilstacy@xxxxxxxxx>]

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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