[TenTec] Orion and RX-320 on DRM

[Paul Christensen]

> > 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