On Wed, 31 Oct 2018 08:29:26 GMT, <698839253X6D445TD@nospam.org> wrote:>John Larkin wrote >>We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>FM. The carrier could be in the 500 MHz to 1 GHz range maybe. >> >>I can get the VCO. What's a good way to do the FM discriminator these >>days? >> >>I could homebrew a quadrature detector, with some resonator and an XOR >>gate or a mixer, but there must be some easier way to do it. Not being >>an RF type, I'd appreciate suggestions. > >PLL >Foster Seeley >Ratio detector >If you are really good at fast pulses (I think you claimed that) >use a fixed length oneshot at zero crossings of the 500 MHz, and lowpass the pulses to 50 MHz. >Disadvantage of tha tmethod is that any interrupts in the signal will cause huge spikes, >so you need to describe your transmission path. > >I've done the one-shot thing at low frequencies. If you use two one-shots, on opposite signal edges, and sum their outputs, you can get twice the one-shot frequency and zero ripple at the center frequency, which is sort of fun. That makes the filtering a lot easier. 500 MHz would get interesting. I'd need a few ps width jitter on the one-shots, which I can do, but I'd need serious width stability vs frequency too. Gotta think about that. I guess you could divide by two and fire four one-shots. -- John Larkin Highland Technology, Inc lunatic fringe electronics
wideband FM demodulator
Started by ●October 31, 2018
Reply by ●October 31, 20182018-10-31
Reply by ●October 31, 20182018-10-31
On 2018-10-30 22:36, Phil Hobbs wrote:> On 10/31/18 12:52 AM, John Larkin wrote: >> >> >> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. >> >> I can get the VCO. What's a good way to do the FM discriminator these >> days? >> >> I could homebrew a quadrature detector, with some resonator and an XOR >> gate or a mixer, but there must be some easier way to do it. Not being >> an RF type, I'd appreciate suggestions. >> >> > For bandwidths that wide, I'd be looking at a delay discriminator. In > the lab that would be a coax cable and a MCL mixer. >That is how it's done in FM ultrawide bandwidth radio (UWB). Page 26 here: https://infoscience.epfl.ch/record/253250/files/EPFL_TH8399.pdf?subformat=pdfa&version=1 If the signal is always strong and of more or less constant amplitude a simple phase discriminator in an FPGA plus an external delay line might suffice: https://www.ece.ucdavis.edu/hsics/files/2015/04/2015_A-10-GHz-Delay-Line-Frequency-Discriminator-and-PD-CP-based-CMOS-Phase-Noise-Measurement-Circuit-with-138.6-dBc_Hz-Sensitivity-at-1-MHz-Offset.pdf High precision will be a challenge because most delay lines are temperature sensitive. Then there either has to be an occasional "pilot tone" for auto-calibration or a 2nd thermally coupled delay line and phase detector with a reference signal going into it. Plus a heater underneath (meander trace, resistor, FET, or other). Wide bandwidth SAW filters might also be useful and save real estate. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 31, 20182018-10-31
On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highlandtechnology.com> wrote: > >> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. > >> I can get the VCO. What's a good way to do the FM discriminator these >> days? > >> I could homebrew a quadrature detector, with some resonator and an XOR >> gate or a mixer, but there must be some easier way to do it. Not being >> an RF type, I'd appreciate suggestions. > >You have a scope with an isolated ground. Take it apart and find out how it >works. > >There's probably a patent somewhere. But scopes don't need a lot of linearity or dynamic range. Most are barely 8 bit machines. They can, probably do, put a switchable attenuator ahead of the FM isolation link. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 31, 20182018-10-31
On 10/31/18 2:08 PM, John Larkin wrote:> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote: > >> John Larkin <jjlarkin@highlandtechnology.com> wrote: >> >>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. >> >>> I can get the VCO. What's a good way to do the FM discriminator these >>> days? >> >>> I could homebrew a quadrature detector, with some resonator and an XOR >>> gate or a mixer, but there must be some easier way to do it. Not being >>> an RF type, I'd appreciate suggestions. >> >> You have a scope with an isolated ground. Take it apart and find out how it >> works. >> >> > > There's probably a patent somewhere. > > But scopes don't need a lot of linearity or dynamic range. Most are > barely 8 bit machines. They can, probably do, put a switchable > attenuator ahead of the FM isolation link.The dominant distortion of a delay discriminator running at constant amplitude is cubic. That can be corrected using a second discriminator with three times the delay, and adding something like 1/3! of its output to the first one. (The trigonometric series isn't the same as the Maclaurin series.) That would leave the dominant distortion as fifth-order, which ought to be small enough to ignore. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●October 31, 20182018-10-31
On Wed, 31 Oct 2018 15:44:30 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/31/18 2:08 PM, John Larkin wrote: >> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote: >> >>> John Larkin <jjlarkin@highlandtechnology.com> wrote: >>> >>>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. >>> >>>> I can get the VCO. What's a good way to do the FM discriminator these >>>> days? >>> >>>> I could homebrew a quadrature detector, with some resonator and an XOR >>>> gate or a mixer, but there must be some easier way to do it. Not being >>>> an RF type, I'd appreciate suggestions. >>> >>> You have a scope with an isolated ground. Take it apart and find out how it >>> works. >>> >>> >> >> There's probably a patent somewhere. >> >> But scopes don't need a lot of linearity or dynamic range. Most are >> barely 8 bit machines. They can, probably do, put a switchable >> attenuator ahead of the FM isolation link. > >The dominant distortion of a delay discriminator running at constant >amplitude is cubic. That can be corrected using a second discriminator >with three times the delay, and adding something like 1/3! of its output >to the first one. (The trigonometric series isn't the same as the >Maclaurin series.) That would leave the dominant distortion as >fifth-order, which ought to be small enough to ignore. > >Cheers > >Phil HobbsThere's a faction here that just wants to digitize the signal at 250 Ms/s and ship it as 8B10B serial data. Makes some sense. The ADC will cost $60 or so, but it's a lot easier to think about than FM. I took one course in communications theory and it was hard. Some fun dithering things could be done to keep me amused from an otherwise boring digital design. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 31, 20182018-10-31
On 2018-10-31 13:04, John Larkin wrote:> On Wed, 31 Oct 2018 15:44:30 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/31/18 2:08 PM, John Larkin wrote: >>> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote: >>> >>>> John Larkin <jjlarkin@highlandtechnology.com> wrote: >>>> >>>>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>>>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. >>>> >>>>> I can get the VCO. What's a good way to do the FM discriminator these >>>>> days? >>>> >>>>> I could homebrew a quadrature detector, with some resonator and an XOR >>>>> gate or a mixer, but there must be some easier way to do it. Not being >>>>> an RF type, I'd appreciate suggestions. >>>> >>>> You have a scope with an isolated ground. Take it apart and find out how it >>>> works. >>>> >>>> >>> >>> There's probably a patent somewhere. >>> >>> But scopes don't need a lot of linearity or dynamic range. Most are >>> barely 8 bit machines. They can, probably do, put a switchable >>> attenuator ahead of the FM isolation link. >> >> The dominant distortion of a delay discriminator running at constant >> amplitude is cubic. That can be corrected using a second discriminator >> with three times the delay, and adding something like 1/3! of its output >> to the first one. (The trigonometric series isn't the same as the >> Maclaurin series.) That would leave the dominant distortion as >> fifth-order, which ought to be small enough to ignore. >> >> Cheers >> >> Phil Hobbs > > There's a faction here that just wants to digitize the signal at 250 > Ms/s and ship it as 8B10B serial data. Makes some sense.But it's too pedestrian. There has to be some sportsmanship in engineering. The ADC will> cost $60 or so, ...Ouch. Why that much? Lots of bits?> ... but it's a lot easier to think about than FM. I took > one course in communications theory and it was hard. > > Some fun dithering things could be done to keep me amused from an > otherwise boring digital design. >FM with a delay discriminator should be easy but wouldn't just PWM-ing it over be enough? -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 31, 20182018-10-31
onsdag den 31. oktober 2018 kl. 21.04.57 UTC+1 skrev John Larkin:> On Wed, 31 Oct 2018 15:44:30 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 10/31/18 2:08 PM, John Larkin wrote: > >> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote: > >> > >>> John Larkin <jjlarkin@highlandtechnology.com> wrote: > >>> > >>>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using > >>>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. > >>> > >>>> I can get the VCO. What's a good way to do the FM discriminator these > >>>> days? > >>> > >>>> I could homebrew a quadrature detector, with some resonator and an XOR > >>>> gate or a mixer, but there must be some easier way to do it. Not being > >>>> an RF type, I'd appreciate suggestions. > >>> > >>> You have a scope with an isolated ground. Take it apart and find out how it > >>> works. > >>> > >>> > >> > >> There's probably a patent somewhere. > >> > >> But scopes don't need a lot of linearity or dynamic range. Most are > >> barely 8 bit machines. They can, probably do, put a switchable > >> attenuator ahead of the FM isolation link. > > > >The dominant distortion of a delay discriminator running at constant > >amplitude is cubic. That can be corrected using a second discriminator > >with three times the delay, and adding something like 1/3! of its output > >to the first one. (The trigonometric series isn't the same as the > >Maclaurin series.) That would leave the dominant distortion as > >fifth-order, which ought to be small enough to ignore. > > > >Cheers > > > >Phil Hobbs > > There's a faction here that just wants to digitize the signal at 250 > Ms/s and ship it as 8B10B serial data. Makes some sense. The ADC will > cost $60 or so,how many bits?
Reply by ●October 31, 20182018-10-31
John Larkin wrote:> We're thinking of sending a wideband (say, dc to 50 MHz) signal using > FM. The carrier could be in the 500 MHz to 1 GHz range maybe. > > I can get the VCO. What's a good way to do the FM discriminator these > days? > > I could homebrew a quadrature detector, with some resonator and an XOR > gate or a mixer, but there must be some easier way to do it. Not being > an RF type, I'd appreciate suggestions.I requested an RF chapter in AOE3 but...oh well.
Reply by ●November 1, 20182018-11-01
John Larkin <jjlarkin@highland_snip_technology.com> wrote:> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote:>>John Larkin <jjlarkin@highlandtechnology.com> wrote:>>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe.>>> I can get the VCO. What's a good way to do the FM discriminator these >>> days?>>> I could homebrew a quadrature detector, with some resonator and an XOR >>> gate or a mixer, but there must be some easier way to do it. Not being >>> an RF type, I'd appreciate suggestions.>>You have a scope with an isolated ground. Take it apart and find out how >>it works.> There's probably a patent somewhere.If you understand patent claims, you can easily find a way around them. There are probably many patents for transferring information across a barrier. Even a slight difference constitutes a different invention. This is how pharmaceutical companies get new patents on virtually identical products. Your application is different, therefore most existing patents won't apply.> But scopes don't need a lot of linearity or dynamic range. Most are > barely 8 bit machines. They can, probably do, put a switchable > attenuator ahead of the FM isolation link.True, but that has nothing to do with your application.
Reply by ●November 1, 20182018-11-01
On 2018-10-31 22:44, Steve Wilson wrote:> John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> On Wed, 31 Oct 2018 06:22:49 GMT, Steve Wilson <no@spam.com> wrote: > >>> John Larkin <jjlarkin@highlandtechnology.com> wrote: > >>>> We're thinking of sending a wideband (say, dc to 50 MHz) signal using >>>> FM. The carrier could be in the 500 MHz to 1 GHz range maybe. > >>>> I can get the VCO. What's a good way to do the FM discriminator these >>>> days? > >>>> I could homebrew a quadrature detector, with some resonator and an XOR >>>> gate or a mixer, but there must be some easier way to do it. Not being >>>> an RF type, I'd appreciate suggestions. > >>> You have a scope with an isolated ground. Take it apart and find out how >>> it works. >Often that's just synchronous AM. Which may also be doable in John's case but hard to say without knowing dynamic range specs and stuff.>> There's probably a patent somewhere. > > If you understand patent claims, you can easily find a way around them. > There are probably many patents for transferring information across a > barrier. Even a slight difference constitutes a different invention. This > is how pharmaceutical companies get new patents on virtually identical > products. Your application is different, therefore most existing patents > won't apply. >Most patents these days are broad grab attempts along the lines of "Let's throw all these spaghetti at the wall and see which ones stick". It is assumed that litigation will weed out bad claims or maybe whole patents.>> But scopes don't need a lot of linearity or dynamic range. Most are >> barely 8 bit machines. They can, probably do, put a switchable >> attenuator ahead of the FM isolation link. > > True, but that has nothing to do with your application. >I may be wrong but I doubt that they have an FM link. -- Regards, Joerg http://www.analogconsultants.com/
