Re: Envelope Detection

Al Clark wrote:

...

If I need a Hilbert transform that extends over a very large frequency range, I use remez exchange to minimize the ripple. The catch is that you don't get to throw out every other coefficient since in general, all the coefficients are non zero.

I concluded, from the few simulations I ran, that a filter with alternate zeros, while longer than an optimized filter of the same ripple, has fewer taps that need computing.* It isn't that multiplying by zero is easy; by marching through the data buffer with a stride of two, the zeros might as well not exist. Windows that best remove ripple reduce bandwidth the most, requiring more taps to get it back.

I think that sometimes people forget that it takes a very long filter to create a 90 degree phase shift at low frequency. It's easy to visualize why if you think about how to create a 90 degree phase shift at DC.

I've had a computer tied up since New Years calculating a filter to do that. :-)

The other thing that I find is that in many cases I actually don't need the envelope, I just need the mean squared (I^2 + Q^2) vs SQRT(I^2 + Q^
2). In a detector, I might just compare the result to some arbitrary level. This means I can skip the SQRT.

I've seen programs that calculate the square root and then convert to decibels.

Jerry
___________________________
* "My mind is made up. Don't confuse me with facts"
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
.

Relevant Pages

  • Re: AC to DC 65+ volts 60 amp Power Supply Plans?
    ... ripple can be much more tolerable, but it's still a lot of capacitance ... is find a big 2:1 transformer and rectify and filter it. ... center-tapped full wave rectifier. ... But if you can get a 20 millihenry 60 amp choke, ...
    (sci.electronics.design)
  • Re: AC to DC 65+ volts 60 amp Power Supply Plans?
    ... The maximum input is 141 VDC and 60 amps. ... incorrectly if there is any ripple or pulsing present. ... ripple can be much more tolerable, but it's still a lot of capacitance ... is find a big 2:1 transformer and rectify and filter it. ...
    (sci.electronics.design)
  • Re: Filtering a tachometer generator
    ... the ripple is easily dealt with. ... The filter needed to smooth the ripple at 1 rpm ... > filter whose cutoff and group delay track the motor speed. ... filter heavily so that your system works well at low speeds. ...
    (comp.dsp)
  • Re: Ripple / ripple rippple : 11 vAC RMS
    ... Originally it just had capacitor 40u filter on B+, ... I added a 9h choke to the preamp B+1 path ... and has 11vAC RMS ripple ... put the choke in front of the first cap. ...
    (alt.guitar.amps)
  • Re: Excelsior! Objective Complete.
    ... about .63 VAC and I got the ripple on the bias from 172 mVAC 60 Hz ... Simple fix: add more Caps. ... to filter because of the rise and fall time aka RC constant. ...
    (alt.guitar.amps)