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.I did an analysis of quadrature detectors and uploaded the results: https://drive.google.com/file/d/1FATlfDya1XrfG8i5vdSxRPbdJv5T-Gh7/view? usp=sharing Here is the readme file: Out of curiosity, I decided to investigate the delay discriminator. Here are the results. 4D620E45 ASC DBM Double Balanced Mixer Max Output The first task is to analyze the Double Balanced Mixer (DBM). Some believe if you drive it harder, you can increase the output. This is true, to an extent. Soon, you reach the point where it starts to saturate. The reason is the DBM acts like two diodes back-to-back. If you drive it harder, you are just pushing against the forward bias curve of a diode. 4D620F40 ASC DBM Delay Discriminator Here is the delay discriminator using a DBM showing the classic S-curve of a phase detector. The signal swings between 400 and 600 kHz. The reason the curve flattens is because the DBM saturates and cannot increase the output. Note the large filter capacitor, C1, needed to smooth the output ripple. This shows the DBM may be useful in a lab setting in a low bandwidth application, but not in an instrument application requiring wide bandwidth. 4D622643 ASC XOR Delay Discriminator An XOR gate can be used as a discriminator, but the sensitivity is much lower. Here the frequency swing is from 300 to 700 kHz, with about 2 V p-p output. 4D627281 ASC MC4044 Delay Discriminator Phase detector #2 in the MC4044 is also a quadrature detector. Here the frequency swing is 400 to 600 kHz, with an output of about 500 mV p-p. Conclusion The delay discriminator can be useful in a lab setting, but the filtering required to reduce the output ripple restricts the application to low bandwidth applications.
wideband FM demodulator
Started by ●October 31, 2018
Reply by ●November 2, 20182018-11-02
Reply by ●November 3, 20182018-11-03
On Friday, November 2, 2018 at 8:36:00 AM UTC-7, John Larkin wrote:> It's not characterized as a delay line. It's apparently intended to > provide a 90 degree phase shift that's independent of frequency. Not > the basis of an FM discriminator.Heh, good point. If you want a voltage proportional to frequency deviation you probably shouldn't start with an allpass network. -- john, KE5FX
Reply by ●November 3, 20182018-11-03
On 11/02/2018 02:16 PM, John Larkin wrote:> On Fri, 2 Nov 2018 07:58:34 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > >> On Thursday, November 1, 2018 at 4:37:31 PM UTC-4, John Larkin wrote: >>> On Thu, 1 Nov 2018 12:25:10 -0700 (PDT), >>> bloggs.fredbloggs.fred@gmail.com wrote: >>> >>>> On Wednesday, October 31, 2018 at 12:52:08 AM UTC-4, 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. >>>> >>>> 7 bucks https://www.minicircuits.com/pdfs/QBA-07+.pdf >>> >>> How would I use that? >> >> Quadrature signals are mixed, and then lowpass of product is the modulating signal. The linearity is a function of ATN(k) being approximately equal to k, so the smaller the relatively deviation the better. May be better to use 1GHz carrier for 5% deviation. >> > > Mixing fixed 90 degree sine waves makes zero. The Minicircuits part is > designed for minimum phase shift vs frequency. > ><https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700000010.pdf>
Reply by ●November 3, 20182018-11-03
On 11/03/2018 04:56 PM, bitrex wrote:> On 11/02/2018 02:16 PM, John Larkin wrote: >> On Fri, 2 Nov 2018 07:58:34 -0700 (PDT), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >>> On Thursday, November 1, 2018 at 4:37:31 PM UTC-4, John Larkin wrote: >>>> On Thu, 1 Nov 2018 12:25:10 -0700 (PDT), >>>> bloggs.fredbloggs.fred@gmail.com wrote: >>>> >>>>> On Wednesday, October 31, 2018 at 12:52:08 AM UTC-4, 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. >>>>> >>>>> 7 bucks https://www.minicircuits.com/pdfs/QBA-07+.pdf >>>> >>>> How would I use that? >>> >>> Quadrature signals are mixed, and then lowpass of product is the >>> modulating signal. The linearity is a function of ATN(k) being >>> approximately equal to k, so the smaller the relatively deviation the >>> better. May be better to use 1GHz carrier for 5% deviation. >>> >> >> Mixing fixed 90 degree sine waves makes zero. The Minicircuits part is >> designed for minimum phase shift vs frequency. >> >> > > <https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700000010.pdf><https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740000098.pdf>
Reply by ●November 20, 20182018-11-20
On Saturday, November 3, 2018 at 6:46:08 AM UTC+11, Tauno Voipio wrote:> On 2.11.18 20:16, John Larkin wrote: > > On Fri, 2 Nov 2018 07:58:34 -0700 (PDT), > > bloggs.fredbloggs.fred@gmail.com wrote: > > > >> On Thursday, November 1, 2018 at 4:37:31 PM UTC-4, John Larkin wrote: > >>> On Thu, 1 Nov 2018 12:25:10 -0700 (PDT), > >>> bloggs.fredbloggs.fred@gmail.com wrote: > >>> > >>>> On Wednesday, October 31, 2018 at 12:52:08 AM UTC-4, 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. > >>>> > >>>> 7 bucks https://www.minicircuits.com/pdfs/QBA-07+.pdf > >>> > >>> How would I use that? > >> > >> Quadrature signals are mixed, and then lowpass of product is the modulating signal. The linearity is a function of ATN(k) being approximately equal to k, so the smaller the relatively deviation the better. May be better to use 1GHz carrier for 5% deviation. > >> > > > > Mixing fixed 90 degree sine waves makes zero. The Minicircuits part is > > designed for minimum phase shift vs frequency. > > > At frequencies from 500 MHz to 1 GHz the delay is easiest with > just a piece of transmission line. A full wave of 1 GHz will be > about 8 inches of cable. A quarter wave is short enough to be > made of stripline on the PC board.Buried stripline in the PC board is non-dispersive and thus preferred over microstrip on the surface of the PC board. Semi-rigid coaxial cable is nice, but not cheap, and the connectors to get the signal out of the PC board and back in again are even more expensive. The electric constant of the insulator - and thus the delay through the delay line - is temperature dependent and thus variable. Semi-rigid coax uses Teflon/PTFE as it's dielectric, where the effect is small and predictable. https://ieeexplore.ieee.org/document/7508671 I've used alumina-loaded Teflon as a printed circuit board substrate https://www.rogerscorp.com/documents/726/acs/RO4000-Laminates-RO4003C-and-RO4350BData-Sheet.pdf It looks as if you could buy stuff that would go the other way. -- Bill Sloman, Sydney
Reply by ●November 20, 20182018-11-20
On Saturday, November 3, 2018 at 7:04:50 AM UTC+11, George Herold wrote:> On Friday, November 2, 2018 at 3:12:35 PM UTC-4, Phil Hobbs wrote: > > On 11/2/18 11:35 AM, John Larkin wrote: > > > On Thu, 1 Nov 2018 15:11:32 -0700 (PDT), "John Miles, KE5FX" > > > <jmiles@gmail.com> wrote: > > > > > >> On Thursday, November 1, 2018 at 1:37:31 PM UTC-7, John Larkin > > >> wrote: > > >>> On Thu, 1 Nov 2018 12:25:10 -0700 (PDT), > > >>> bloggs.fredbloggs.fred@gmail.com wrote: > > >>> > > >>>> On Wednesday, October 31, 2018 at 12:52:08 AM UTC-4, 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. > > >>>> > > >>>> 7 bucks https://www.minicircuits.com/pdfs/QBA-07+.pdf > > >>> > > >>> How would I use that? > > >> > > >> > > >> That'd be your delay line, used with a mixer to recover the > > >> modulated signal. It'll work but I'd be surprised if it's very > > >> stable. > > > > > > It's not characterized as a delay line. It's apparently intended to > > > provide a 90 degree phase shift that's independent of frequency. Not > > > the basis of an FM discriminator. > > > > > >> > > >> For the case you're describing, straight FM isn't all that common. > > >> I used an MC13155D for something similar at one point but it's gone > > >> the way of the 12AX7 (oh, wait, you can still get those). I wonder > > >> if there's a QAM chipset available with similar bandwidth? > > >> Something comparable to a cable or DSL modem, but without all the > > >> DOCSIS baggage. > > > > > > We've been playing with pushing maybe DC-100 MHz of analog signal > > > over a telecom-type fiber link. I was thinking of using FM, but that > > > might become a nightmare. > > > > Especially in the presence of facet reflections, which cause phase > > nonlinearities just like multipath distortion in radio. If you use > > FC-APC (angled physical contact) connectors, you can get the reflection > > down to ~1% or a bit less, which helps, but if the fibre delay is up > > near your deviation bandwidth there'll be nonlinearity. > > > > > > > Brute force (merely apply money) is an ADC at one end, 8B10B coding, > > > a 6 Gbps fiber link, and a DAC at the far end. Sampling at 300 MHz, > > > 1.5x Nyquist, makes the filtering reasonable. > > > > > > I can buy pretty good VCOs for the transmit end, but their typical > > > modulation bandwidths are low. Then there is the receiver problem. > > > > > > Oh well, back to connecting bricks. > > > > One of our main customers just blew up three lasers that we sent them. > Three!? that takes a special talent. Usually when you fry one you stop > and think about what you are doing.No special talent. Just put a senior manager in the room and everything blows up. In physics it is called the Pauli Effect. http://ffden-2.phys.uaf.edu/211_fall2013.web.dir/kasie_baker/page4.html Apparently his mere presence in the same town (at the railway station in Gottingen) was sufficient. In practice, the pressure to make something happen does seem to be the mechanism. -- Bill Sloman, Sydney
