Jim, I was perusing your website and happened upon your patent regarding demodulating of FSK. Is this the currently easiest/best way to decode FSK? Or would I be better off doing with SW and microcontroller? I was thinking that a comparator with hysteresis to minimize noise could be used to 'square up' the input signal and then I could just use a timer on the uC to count transitions over the bit time. The freqs are 1562.5 and 2083.3 with 520.83 bit/sec rate--- giving 3 or 4, respective, transitions per bit time. Is this a good way to do it or is there another easier/better way? Thanks, Bo PS. Thanks to Tim Wescott for pointing out that you are--not comp.arch.embedded...where I originally posted.
ping: Jim Thompson
Started by ●April 24, 2006
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 10:23:56 -0500, "Bo" <bo@cephus.com> wrote:>Jim, > >I was perusing your website and happened upon your patent regarding >demodulating of FSK. Is this the currently easiest/best way to decode FSK? >Or would I be better off doing with SW and microcontroller?Most now use SW to decode FSK, but the analog approach generally yields better performance in low signal-to-noise situations. When I designed that scheme I was working in the dark ages with acoustic-muff coupling to telephones running at 300-1K Baud ;-)> >I was thinking that a comparator with hysteresis to minimize noise could be >used to 'square up' the input signal and then I could just use a timer on >the uC to count transitions over the bit time. The freqs are 1562.5 and >2083.3 with 520.83 bit/sec rate--- giving 3 or 4, respective, transitions >per bit time. Is this a good way to do it or is there another easier/better >way?Using a comparator on analog signals often aggravates the noise.> >Thanks, > >Bo > >PS. Thanks to Tim Wescott for pointing out that you are--not >comp.arch.embedded...where I originally posted. >...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●April 24, 20062006-04-24
Hello Bo,> I was perusing your website and happened upon your patent regarding > demodulating of FSK. Is this the currently easiest/best way to decode FSK? > Or would I be better off doing with SW and microcontroller? >As Jim said, much of this is now done in firmware. Look at DTMF decoder app notes in the TI MSP430 section or at other uC manufacturers. In my experience the lion's share of this job is to provide a nice matched filter for the FSK tones. Steep yet good pulse response, good time domain behavior and unconditional stability. Wave digital filters are quite efficient here. The rest is pretty trivial, usually. Unless you get into esoteric modulation schemes. Regards, Joerg http://www.analogconsultants.com
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 16:50:27 GMT, Joerg <notthisjoergsch@removethispacbell.net> wrote:>Hello Bo, > > >> I was perusing your website and happened upon your patent regarding >> demodulating of FSK. Is this the currently easiest/best way to decode FSK? >> Or would I be better off doing with SW and microcontroller? >> > >As Jim said, much of this is now done in firmware. Look at DTMF decoder >app notes in the TI MSP430 section or at other uC manufacturers. In my >experience the lion's share of this job is to provide a nice matched >filter for the FSK tones. Steep yet good pulse response, good time >domain behavior and unconditional stability. Wave digital filters are >quite efficient here. The rest is pretty trivial, usually. Unless you >get into esoteric modulation schemes. > >Regards, Joerg > >http://www.analogconsultants.comWideband FSK is nontrivial to decode in software. The Bell 202 spec was 1200 baud async, shifting between 1200 to 2200 Hz, so you get very few edges to work with. A decent analog FSK decoder will deliver very nice, low jitter 1200 baud serial data here. John
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 11:47:43 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Mon, 24 Apr 2006 16:50:27 GMT, Joerg ><notthisjoergsch@removethispacbell.net> wrote: > >>Hello Bo, >> >> >>> I was perusing your website and happened upon your patent regarding >>> demodulating of FSK. Is this the currently easiest/best way to decode FSK? >>> Or would I be better off doing with SW and microcontroller? >>> >> >>As Jim said, much of this is now done in firmware. Look at DTMF decoder >>app notes in the TI MSP430 section or at other uC manufacturers. In my >>experience the lion's share of this job is to provide a nice matched >>filter for the FSK tones. Steep yet good pulse response, good time >>domain behavior and unconditional stability. Wave digital filters are >>quite efficient here. The rest is pretty trivial, usually. Unless you >>get into esoteric modulation schemes. >> >>Regards, Joerg >> >>http://www.analogconsultants.com > > >Wideband FSK is nontrivial to decode in software. The Bell 202 spec >was 1200 baud async, shifting between 1200 to 2200 Hz, so you get very >few edges to work with. A decent analog FSK decoder will deliver very >nice, low jitter 1200 baud serial data here. > >JohnYep. My circuit simply implements the classic "S-curve" discriminator in an active filter manner. Performance in a noisy environment is great! ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 11:51:32 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:>On Mon, 24 Apr 2006 11:47:43 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Mon, 24 Apr 2006 16:50:27 GMT, Joerg >><notthisjoergsch@removethispacbell.net> wrote: >> >>>Hello Bo, >>> >>> >>>> I was perusing your website and happened upon your patent regarding >>>> demodulating of FSK. Is this the currently easiest/best way to decode FSK? >>>> Or would I be better off doing with SW and microcontroller? >>>> >>> >>>As Jim said, much of this is now done in firmware. Look at DTMF decoder >>>app notes in the TI MSP430 section or at other uC manufacturers. In my >>>experience the lion's share of this job is to provide a nice matched >>>filter for the FSK tones. Steep yet good pulse response, good time >>>domain behavior and unconditional stability. Wave digital filters are >>>quite efficient here. The rest is pretty trivial, usually. Unless you >>>get into esoteric modulation schemes. >>> >>>Regards, Joerg >>> >>>http://www.analogconsultants.com >> >> >>Wideband FSK is nontrivial to decode in software. The Bell 202 spec >>was 1200 baud async, shifting between 1200 to 2200 Hz, so you get very >>few edges to work with. A decent analog FSK decoder will deliver very >>nice, low jitter 1200 baud serial data here. >> >>John > >Yep. My circuit simply implements the classic "S-curve" discriminator >in an active filter manner. Performance in a noisy environment is >great! > > ...Jim ThompsonI like using a 90+-x degree phase shifter (which turns out to be a very peaky 2-pole lowpass filter) followed by an xor, then a lowpass, then a comparator. But FSK is going away. QAM and constellations and such are faster and easier to decode digitally. John
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 12:04:26 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Mon, 24 Apr 2006 11:51:32 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote: > >>On Mon, 24 Apr 2006 11:47:43 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Mon, 24 Apr 2006 16:50:27 GMT, Joerg >>><notthisjoergsch@removethispacbell.net> wrote: >>> >>>>Hello Bo, >>>> >>>> >>>>> I was perusing your website and happened upon your patent regarding >>>>> demodulating of FSK. Is this the currently easiest/best way to decode FSK? >>>>> Or would I be better off doing with SW and microcontroller? >>>>> >>>> >>>>As Jim said, much of this is now done in firmware. Look at DTMF decoder >>>>app notes in the TI MSP430 section or at other uC manufacturers. In my >>>>experience the lion's share of this job is to provide a nice matched >>>>filter for the FSK tones. Steep yet good pulse response, good time >>>>domain behavior and unconditional stability. Wave digital filters are >>>>quite efficient here. The rest is pretty trivial, usually. Unless you >>>>get into esoteric modulation schemes. >>>> >>>>Regards, Joerg >>>> >>>>http://www.analogconsultants.com >>> >>> >>>Wideband FSK is nontrivial to decode in software. The Bell 202 spec >>>was 1200 baud async, shifting between 1200 to 2200 Hz, so you get very >>>few edges to work with. A decent analog FSK decoder will deliver very >>>nice, low jitter 1200 baud serial data here. >>> >>>John >> >>Yep. My circuit simply implements the classic "S-curve" discriminator >>in an active filter manner. Performance in a noisy environment is >>great! >> >> ...Jim Thompson > >I like using a 90+-x degree phase shifter (which turns out to be a >very peaky 2-pole lowpass filter) followed by an xor, then a lowpass, >then a comparator. > >But FSK is going away. QAM and constellations and such are faster and >easier to decode digitally. > >JohnThose who bother to study my patent will see that I very cleverly derive the 90� directly from the gyrator-based filter... thus all the filtering and shifting is done simultaneously ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●April 24, 20062006-04-24
Jim Thompson wrote: ...> Using a comparator on analog signals often aggravates the noise.Even with enough hysteresis? ... Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●April 24, 20062006-04-24
On Mon, 24 Apr 2006 15:11:09 -0400, Jerry Avins <jya@ieee.org> wrote:>Jim Thompson wrote: > > ... > >> Using a comparator on analog signals often aggravates the noise. > >Even with enough hysteresis? > > ... > >Jerry1200 baud FSK changes frequency in a _single_ cycle, so period-type demodulation goes to crap quickly in the presence of noise. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●April 24, 20062006-04-24
Jim Thompson wrote:> On Mon, 24 Apr 2006 15:11:09 -0400, Jerry Avins <jya@ieee.org> wrote: > > >>Jim Thompson wrote: >> >> ... >> >> >>>Using a comparator on analog signals often aggravates the noise. >> >>Even with enough hysteresis? >> >> ... >> >>Jerry > > > 1200 baud FSK changes frequency in a _single_ cycle, so period-type > demodulation goes to crap quickly in the presence of noise.Shades of the tape interface on my KIM-1 and its successors. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
