> > signals for audio signals. A 0.1 cap is large even for 12 kHz.
>
> I'm not having a problem with not enough signal. Even with the cap in
place,
> I still need to back down on the soundcard input level to keep the input
> from overloading.
Mark -- I believe what Carl is indicating is that a 0.1 uF bypass cap to
ground at the I.F. jack may be severely attenuating the higher DRM
frequencies. The higher the source Z from the RX-320, the more critical the
value of the bypass capacitor. For example, if the I.F. source Z is 2K-ohm
(typical of IHF level consumer-grade RCA outputs), the 3 dB turnover point
calculates to the following formula:
f (-3dB) = 1/(2 Pi RC); where R is in Ohms and C is in Farads.
At 2K-ohm, the turnover point is already down 3 dB at 796 Hz. For DRM, you
have to ensure that the I.F. output source Z is no more than 120 ohms in
order to be comfortable with a 0.1 uF bypass capacitor. The only way of
knowing this is examining the I.F. pick-off point of the circuit. Unless
the RX-320 I.F. jack is capacitivly coupled to a low-Z active output stage,
I would have a hard time believing that a 0.1 uF bypass capacitor is not
degrading DRM performance.
-Paul, W9AC
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