[AMRadio] HRO question for the day


John Coleman jc at pctechref.com
Fri Dec 18 17:09:22 EST 2009


Jim

After looking over your web document. As I see it then the slew distortion
is caused by the RF bypass capacitor's inability to discharge fast enough to
follow the shape of the audio as it falls.  Or, you might say the inability
of the load resistor to discharge the capacitor fast enough.  If that is the
case then it probably effects the higher modulating frequencies more that
the lower ones.  The Audio bypass is chosen to reduce the RF component of
the rectified output to some acceptable value.  If that is true then the
circuit design could be improved by starting with a higher IF frequency.  I
would think that the greater ratios of RF to audio frequency would lend its
self to a lower time constant there by extending the frequency range of the
less distorted audio,  Assuming I am on tr5ack here, perhaps one thing that
might help is a full wave detector.  Two diodes on a center tapped secondary
IF XFMR.  A smaller bypass capacitor could be used because the RF ripple
would be twice the original IF frequency.

Am I on track with any of this detector thinking?

Do active detectors or DBL Bal product detectors have similar problems?
My guess is that they do, but probably not as noticeable except at lower RF
to AF frequency ratios.

I know many folks that would say "it isn't that important" and to some
degree they are right but it doesn't stop me from trying to understand and
design something that is a little better.  My fun in this hobby is in the
design and modification aspect.  Even if no one can tell the difference, it
helps me to understand.

John, WA5BXO 



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