[App_rpt-users] USB sound FOB lack of high frequency noise

[Sam Skolfield]

Sounds like a lousy anti-aliasing LPF. Loose tolerance, poor design, maybe
both.....



On Wed, May 4, 2016 at 8:43 PM, Skyler F <electricity440 at gmail.com> wrote:

> I figured out the problem : Even though I was hooking my audio directly
> into the mic input of the CM108 chip, a low pass filter was clamping all
> the high frequency signals to ground, I just had to desolder an L5 as this
> link shows:
>
> http://m3h.com/usbfob-119.pdf
>
> I was looking at other guides, which had sound fobs with no low pass
> filter already in it.
>
> kdw0hb
>
>
> On Tue, May 3, 2016 at 8:34 AM, Skyler F <electricity440 at gmail.com> wrote:
>
>> I just put together a modified sound fob by taking a 10µF capacitor to
>> the divider of 47k and 68k resistors and then to the microphone input of
>> the sound fob, but I am getting the lack of high frequency noise error when
>> I plug my fob into the radio. A DMK URI works fine. Has anybody else had
>> problems with these sound fobs?
>>
>> 73
>> kd0whb
>>
>
>
>
> --
> Skyler Fennell
> amsatnet.info
> KDØWHB
> electricity440 at gmail.com
>
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-- 
KJ6QFS
Sam Skolfield
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