On Fri, 19 May 2006 18:21:39 +0800, Steve Underwood <steveu@dis.org> wrote:>Rick Lyons wrote:(snipped)>> >> I just learned of a new (new to me) efficient >> I/Q sampling scheme proposed twenty years >> ago by DSP pioneer Charles Rader. >> He uses two all-pass filters that have >> a 90-degree phase shift between them. Rader's >> paper is: >> [C. M. Rader, "A Simple Method for Sampling In- >> Phase and Quadrature Components," IEEE Trans. Aerospace >> and Electronic Syst.,vol. 20, no. 6, pp. 821-824, >> Nov. 1984.] > >I haven't seen the paper, but can you explain the novelty in a couple of >sentances? You said all-pass, but surely if they are all pass you only >need one filter - a hilbert transformer. In comms systems I and Q and >often created by using a pair of filters to pulse shape the signal, and >provide 90 degree different phase shifts at the same time. That's neat, >because you kill two birds with one stone. Is that the kind of thing you >mean, because I think the cavemen were using that technique?Hi Steve, Rader's scheme uses just one A/D converter and two filters having a 90-degree phase difference (as you said). What made Rader's method neat was that he had a way to provide built-in decimation at no computational cost. [When I get the time, I want to model Rader's idea with MATLAB to see how well it works.] I searched the Web for an electronic copy of Rader's paper, but failed to find any website where you can download a copy of his paper. Now Steve, if you've just won the Lottery then you can afford to sign up for the IEEE Explore program and download a copy of Rader's paper. Regards, [-Rick-]
Complex Sampling Techniques
Started by ●May 18, 2006
Reply by ●May 20, 20062006-05-20
Reply by ●May 20, 20062006-05-20
Jerry Avins wrote:> Steve Underwood wrote: > > ... > A pair of matched-amplitude all-pass filters whose outputs are in > quadrature (but neither of which is linear phase) can be computationally > cheaper than a low-ripple broadband Hilbert transformer. I know how to > make the filter pair with analog circuits (three op-amps each for a > decade bandwidth), I've never even heard of an analog HT. >I am not an expert in analog circuits, but thinking/looking for this I've just come across some tutorial/paper at http://members.tripod.com/michaelgellis/mixerscom.html by Michael Ellis, which shows some rather frighteningly-looking analog networks for phase splitting/shifting. I wonder if such things are/were really used (and work(ed) adequately)... Regards, Dmitry.
Reply by ●May 20, 20062006-05-20
Dmitry Utyansky wrote:> Jerry Avins wrote: > >>Steve Underwood wrote: >> >> ... >>A pair of matched-amplitude all-pass filters whose outputs are in >>quadrature (but neither of which is linear phase) can be computationally >>cheaper than a low-ripple broadband Hilbert transformer. I know how to >>make the filter pair with analog circuits (three op-amps each for a >>decade bandwidth), I've never even heard of an analog HT. >> > > > I am not an expert in analog circuits, but thinking/looking for this > I've just come across some tutorial/paper at > http://members.tripod.com/michaelgellis/mixerscom.html by Michael > Ellis, which shows some rather frighteningly-looking analog networks > for phase splitting/shifting.None of them look very frightening, but maybe I'm just more fearless than I realise :-) Figure 14 looks fun, though.> > I wonder if such things are/were really used (and work(ed) > adequately)...They were certainly used, and I'm sure still are in many places. Steve
Reply by ●May 21, 20062006-05-21
Dmitry Utyansky wrote:> Jerry Avins wrote: > >>Steve Underwood wrote: >> >> ... >>A pair of matched-amplitude all-pass filters whose outputs are in >>quadrature (but neither of which is linear phase) can be computationally >>cheaper than a low-ripple broadband Hilbert transformer. I know how to >>make the filter pair with analog circuits (three op-amps each for a >>decade bandwidth), I've never even heard of an analog HT. >> > > > I am not an expert in analog circuits, but thinking/looking for this > I've just come across some tutorial/paper at > http://members.tripod.com/michaelgellis/mixerscom.html by Michael > Ellis, which shows some rather frighteningly-looking analog networks > for phase splitting/shifting. > > I wonder if such things are/were really used (and work(ed) > adequately)...Yes. Three all-passes in each leg give a 90-degree relative shift over a decade with about a quarter-degree peak error. I've designed them and you may find on in the ARRL handbook. It was there several years ago. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 23, 20062006-05-23
Rick Lyons wrote:> On Fri, 19 May 2006 18:21:39 +0800, Steve Underwood <steveu@dis.org> > wrote: > > >Rick Lyons wrote: > (snipped) > >> > >> I just learned of a new (new to me) efficient > >> I/Q sampling scheme proposed twenty years > >> ago by DSP pioneer Charles Rader. > >> He uses two all-pass filters that have > >> a 90-degree phase shift between them. Rader's > >> paper is:.> >> [C. M. Rader, "A Simple Method for Sampling In-> >> Phase and Quadrature Components," IEEE Trans. Aerospace > >> and Electronic Syst.,vol. 20, no. 6, pp. 821-824, > >> Nov. 1984.]<snip>> Now Steve, if you've just won the Lottery then you > can afford to sign up for the IEEE Explore program > and download a copy of Rader's paper.Sadly, not even the Lottery will help. I just tried IEEE Explore and was puzzled not to succeed in finding it there. Finally a peek at their FAQ explains that it provides only: * IEEE journals, transactions, letters, and magazines from 1988 with select content back to 1952 * IEEE conference proceedings from 1988 with select content back to 1953 * IEEE standards from 1988 * IEE journals, letters, and magazines from 1988 * IEE conference proceedings from 1988
Reply by ●May 23, 20062006-05-23
Jerry Wolf wrote:> Rick Lyons wrote: > >>On Fri, 19 May 2006 18:21:39 +0800, Steve Underwood <steveu@dis.org> >>wrote: >> >> >>>Rick Lyons wrote: >> >> (snipped) >> >>>>I just learned of a new (new to me) efficient >>>>I/Q sampling scheme proposed twenty years >>>>ago by DSP pioneer Charles Rader. >>>>He uses two all-pass filters that have >>>>a 90-degree phase shift between them. Rader's >>>>paper is: > > .> >> [C. M. Rader, "A Simple Method for Sampling In- > >>>>Phase and Quadrature Components," IEEE Trans. Aerospace >>>>and Electronic Syst.,vol. 20, no. 6, pp. 821-824, >>>>Nov. 1984.] > > > <snip> > >>Now Steve, if you've just won the Lottery then you >>can afford to sign up for the IEEE Explore program >>and download a copy of Rader's paper. > > > Sadly, not even the Lottery will help. I just tried IEEE Explore and > was puzzled not to succeed in finding it there. Finally a peek at > their FAQ explains that it provides only: > * IEEE journals, transactions, letters, and magazines from 1988 > with select content back to 1952 > * IEEE conference proceedings from 1988 with select content back to > 1953 > * IEEE standards from 1988 > * IEE journals, letters, and magazines from 1988 > * IEE conference proceedings from 1988 >Darned good thing I kept the lottery money in my Swiss bank accounts, then. :-) Steve
