Please note quotation marks in subject ;)
Also, I'm not the oldest on group --- BUT
my father operated a *LEGAL* land based spark gap xmtr
All that to say that I think in "linear passive discrete" domain
rather than in "digital" domain.
I have a "filter" problem.
I have a reasonable idea on how to implement it.
*UNFORTUNATELY* requires HENRY's and FARADs ;/
I can write and solve the associated mesh equations
My solution will obviously be a subset of SPICE
BUT will I be able to describe either
PROBLEM or SOLUTION
to those educated in digital domain?
{for perspective -searching this group will reveal that I once
threatened to implement FFT in COBOL ;\ }
0
Is there a "DIGITAL" equivalent of "Q"?
Started by ●April 26, 2010
Reply by ●April 26, 20102010-04-26
On Apr 26, 3:55�pm, Richard Owlett <rowl...@pcnetinc.com> wrote:> Please note quotation marks in subject ;) > Also, I'm not the oldest on group --- BUT > � �my father operated a *LEGAL* land based spark gap xmtr > > All that to say that I think in "linear passive discrete" domain > rather than in "digital" domain. > > I have a "filter" problem. > I have a reasonable idea on how to implement it. > *UNFORTUNATELY* requires HENRY's and FARADs ;/ > I can write and solve the associated mesh equations > My solution will obviously be a subset of SPICE > > BUT will I be able to describe either > PROBLEM or SOLUTION > to those educated in digital domain? > > {for perspective -searching this group will reveal that I once > threatened to implement FFT in COBOL ;\ } > > 0if you provide a frequency response and phase response (if you care) or a time domain response to the DSP person, they will be able to design your filter.. or you can try it yourself http://www.mds.com/download/filterdesign.asp with a free demo version (very) basically, selectivity relates to the number of taps.. higher selectivity = more taps... Mark
Reply by ●April 26, 20102010-04-26
Richard Owlett wrote:> Please note quotation marks in subject ;) > Also, I'm not the oldest on group --- BUT > my father operated a *LEGAL* land based spark gap xmtr > > All that to say that I think in "linear passive discrete" domain rather > than in "digital" domain. > > I have a "filter" problem. > I have a reasonable idea on how to implement it. > *UNFORTUNATELY* requires HENRY's and FARADs ;/ > I can write and solve the associated mesh equations > My solution will obviously be a subset of SPICE > > BUT will I be able to describe either > PROBLEM or SOLUTION > to those educated in digital domain? > > {for perspective -searching this group will reveal that I once > threatened to implement FFT in COBOL ;\ }Q is a very nice number for 2nd-order time-invariant linear resonant systems (such as you might make with caps and coils). It's nice because it expresses a ratio that holds over a very wide range, and it has the same meaning for a system with a resonant frequency at 1Hz as a system with a resonant frequency at 1GHz. It's also more or less easily extensible to 3rd, 4th, and even infinite-order (i.e. transmission line) systems. It doesn't work so well with sampled time systems. There is sort of a concept of Q buried in there, but the closer you get to the sampling rate, the more "kinda" it gets. It is _not_ a nice convenient invariant ratio for a resonant frequency that changes with respect to the sampling rate. Alas. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by ●April 26, 20102010-04-26
Mark wrote: Mark wrote:> On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: >> Please note quotation marks in subject ;) >> Also, I'm not the oldest on group --- BUT >> my father operated a *LEGAL* land based spark gap xmtr >> >> All that to say that I think in "linear passive discrete" domain >> rather than in "digital" domain. >> >> I have a "filter" problem. >> I have a reasonable idea on how to implement it. >> *UNFORTUNATELY* requires HENRY's and FARADs ;/ >> I can write and solve the associated mesh equations >> My solution will obviously be a subset of SPICE >> >> BUT will I be able to describe either >> PROBLEM or SOLUTION >> to those educated in digital domain? >> >> {for perspective -searching this group will reveal that I once >> threatened to implement FFT in COBOL ;\ } >> >> 0 > > if you provide a frequency response and phase response (if you care) > or a time domain response to the DSP person, they will be able to > design your filter.. > > or you can try it yourself > > http://www.mds.com/download/filterdesign.asp > > with a free demo version > > (very) basically, selectivity relates to the number of taps.. higher > selectivity = more taps... > > > Mark >> On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: >> Please note quotation marks in subject ;) >> Also, I'm not the oldest on group --- BUT >> my father operated a *LEGAL* land based spark gap xmtr >> >> All that to say that I think in "linear passive discrete" domain >> rather than in "digital" domain. >> >> I have a "filter" problem. >> I have a reasonable idea on how to implement it. >> *UNFORTUNATELY* requires HENRY's and FARADs ;/ >> I can write and solve the associated mesh equations >> My solution will obviously be a subset of SPICE >> >> BUT will I be able to describe either >> PROBLEM or SOLUTION >> to those educated in digital domain? >> >> {for perspective -searching this group will reveal that I once >> threatened to implement FFT in COBOL ;\ } >> >> 0 > > if you provide a frequency response and phase response (if you care) > or a time domain response to the DSP person, they will be able to > design your filter.. > > or you can try it yourself > > http://www.mds.com/download/filterdesign.asp > > with a free demo version > > (very) basically, selectivity relates to the number of taps.. higher > selectivity = more taps... > > > Mark >Thank you for your courteous reply. BUT I am a "curmudgeon" I ask for *EXPLICIT* definition of "Q" in *DIGITAL* domain.
Reply by ●April 27, 20102010-04-27
On Apr 26, 5:12�pm, Richard Owlett <rowl...@pcnetinc.com> wrote:> Mark wrote: > Mark wrote: > > On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: > >> Please note quotation marks in subject ;) > >> Also, I'm not the oldest on group --- BUT > >> � �my father operated a *LEGAL* land based spark gap xmtr > > >> All that to say that I think in "linear passive discrete" domain > >> rather than in "digital" domain. > > >> I have a "filter" problem. > >> I have a reasonable idea on how to implement it. > >> *UNFORTUNATELY* requires HENRY's and FARADs ;/ > >> I can write and solve the associated mesh equations > >> My solution will obviously be a subset of SPICE > > >> BUT will I be able to describe either > >> PROBLEM or SOLUTION > >> to those educated in digital domain? > > >> {for perspective -searching this group will reveal that I once > >> threatened to implement FFT in COBOL ;\ } > > >> 0 > > > if you provide a frequency response and phase response (if you care) > > or a time domain response to the DSP person, they will be able to > > design your filter.. > > > or you can try it yourself > > >http://www.mds.com/download/filterdesign.asp > > > with a free demo version > > > (very) basically, selectivity relates to the number of taps.. �higher > > selectivity = more taps... > > > Mark > > > On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: > >> Please note quotation marks in subject ;) > >> Also, I'm not the oldest on group --- BUT > >> � �my father operated a *LEGAL* land based spark gap xmtr > > >> All that to say that I think in "linear passive discrete" domain > >> rather than in "digital" domain. > > >> I have a "filter" problem. > >> I have a reasonable idea on how to implement it. > >> *UNFORTUNATELY* requires HENRY's and FARADs ;/ > >> I can write and solve the associated mesh equations > >> My solution will obviously be a subset of SPICE > > >> BUT will I be able to describe either > >> PROBLEM or SOLUTION > >> to those educated in digital domain? > > >> {for perspective -searching this group will reveal that I once > >> threatened to implement FFT in COBOL ;\ } > > >> 0 > > > if you provide a frequency response and phase response (if you care) > > or a time domain response to the DSP person, they will be able to > > design your filter.. > > > or you can try it yourself > > >http://www.mds.com/download/filterdesign.asp > > > with a free demo version > > > (very) basically, selectivity relates to the number of taps.. �higher > > selectivity = more taps... > > > Mark > > Thank you for your courteous reply. > BUT I am a "curmudgeon" > I ask for *EXPLICIT* definition of "Q" in *DIGITAL* domain.Perhaps it would be useful if you would tell us how you define Q in the analog domain (there's more than one way).
Reply by ●April 27, 20102010-04-27
cassiope wrote:> On Apr 26, 5:12 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: >> Mark wrote: >> Mark wrote: >>> On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: >>>> Please note quotation marks in subject ;) >>>> Also, I'm not the oldest on group --- BUT >>>> my father operated a *LEGAL* land based spark gap xmtr >>>> All that to say that I think in "linear passive discrete" domain >>>> rather than in "digital" domain. >>>> I have a "filter" problem. >>>> I have a reasonable idea on how to implement it. >>>> *UNFORTUNATELY* requires HENRY's and FARADs ;/ >>>> I can write and solve the associated mesh equations >>>> My solution will obviously be a subset of SPICE >>>> BUT will I be able to describe either >>>> PROBLEM or SOLUTION >>>> to those educated in digital domain? >>>> {for perspective -searching this group will reveal that I once >>>> threatened to implement FFT in COBOL ;\ } >>>> 0 >>> if you provide a frequency response and phase response (if you care) >>> or a time domain response to the DSP person, they will be able to >>> design your filter.. >>> or you can try it yourself >>> http://www.mds.com/download/filterdesign.asp >>> with a free demo version >>> (very) basically, selectivity relates to the number of taps.. higher >>> selectivity = more taps... >>> Mark >>> On Apr 26, 3:55 pm, Richard Owlett <rowl...@pcnetinc.com> wrote: >>>> Please note quotation marks in subject ;) >>>> Also, I'm not the oldest on group --- BUT >>>> my father operated a *LEGAL* land based spark gap xmtr >>>> All that to say that I think in "linear passive discrete" domain >>>> rather than in "digital" domain. >>>> I have a "filter" problem. >>>> I have a reasonable idea on how to implement it. >>>> *UNFORTUNATELY* requires HENRY's and FARADs ;/ >>>> I can write and solve the associated mesh equations >>>> My solution will obviously be a subset of SPICE >>>> BUT will I be able to describe either >>>> PROBLEM or SOLUTION >>>> to those educated in digital domain? >>>> {for perspective -searching this group will reveal that I once >>>> threatened to implement FFT in COBOL ;\ } >>>> 0 >>> if you provide a frequency response and phase response (if you care) >>> or a time domain response to the DSP person, they will be able to >>> design your filter.. >>> or you can try it yourself >>> http://www.mds.com/download/filterdesign.asp >>> with a free demo version >>> (very) basically, selectivity relates to the number of taps.. higher >>> selectivity = more taps... >>> Mark >> Thank you for your courteous reply. >> BUT I am a "curmudgeon" >> I ask for *EXPLICIT* definition of "Q" in *DIGITAL* domain. > > Perhaps it would be useful if you would tell us how you define Q in > the analog domain (there's more than one way).I was thinking in terms of Q = {bandwidth}/{resonant frequency} Question may have become moot as Tim's answer triggered change of how I defined my goals.
Reply by ●April 27, 20102010-04-27
Richard Owlett <rowlett@pcnetinc.com> wrote:>I was thinking in terms of Q = {bandwidth}/{resonant frequency}I'm going to go out on a limb and say center frequency / bandwidth instead. And, even in a digital domain, it's still the same -- resonant frequency divided by the 3 dB bandwidth is still Q. Even if you're close to Fs/2, and the filter shape looks funny. Steve
Reply by ●April 27, 20102010-04-27
Richard Owlett <rowlett@pcnetinc.com> wrote: (snip)> I was thinking in terms of Q = {bandwidth}/{resonant frequency}> Question may have become moot as Tim's answer triggered change of > how I defined my goals.It seems that there are different definitions for Q. Note, for example, the Wikipedia page Q_factor. Some of the difference comes from the difference between filters and oscillators, such that one is: Q = 2 pi * energy store / energy dissipated per cycle. The other is, as noted, (resonant frequency/(bandwidth), each in either cycles or radians. It seems that they are close for high Q, but not so close at lower Q. -- glen
Reply by ●April 28, 20102010-04-28
Steve Pope wrote:> Richard Owlett <rowlett@pcnetinc.com> wrote: > >> I was thinking in terms of Q = {bandwidth}/{resonant frequency} > > I'm going to go out on a limb and say center frequency / bandwidth > instead. > > And, even in a digital domain, it's still the same -- resonant > frequency divided by the 3 dB bandwidth is still Q. Even if > you're close to Fs/2, and the filter shape looks funny.But in the Laplace domain Q is pretty easy to pick off of a 2nd-order characteristic polynomial; this is not so easy and direct in the z-transform world (unless you know something I don't; in which case I'd be happy if you corrected me). -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by ●April 28, 20102010-04-28
On 4/27/2010 11:38 PM, Tim Wescott wrote:> Steve Pope wrote: >> Richard Owlett <rowlett@pcnetinc.com> wrote: >> >>> I was thinking in terms of Q = {bandwidth}/{resonant frequency} >> >> I'm going to go out on a limb and say center frequency / bandwidth >> instead. >> >> And, even in a digital domain, it's still the same -- resonant >> frequency divided by the 3 dB bandwidth is still Q. Even if >> you're close to Fs/2, and the filter shape looks funny. > > But in the Laplace domain Q is pretty easy to pick off of a 2nd-order > characteristic polynomial; this is not so easy and direct in the > z-transform world (unless you know something I don't; in which case I'd > be happy if you corrected me).Steve, I hope you can educate me. Jerry -- "I view the progress of science as ... the slow erosion of the tendency to dichotomize." --Barbara Smuts, U. Mich. �����������������������������������������������������������������������
