Forums

wideband FM demodulator

Started by John Larkin October 31, 2018

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.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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. Cheers Phil Hobbs s -- 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
On 2018-10-31, 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.
SDR -- When I tried casting out nines I made a hash of it.
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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.
> Cheers
> Phil Hobbs
How do you get down to DC with a delay discriminator?
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.
On 10/31/2018 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. > >
So long as your analog signal chain bandwith is sufficient to pass the carrier frequency + /- modulation index you can undersample it to recover the modulated signal directly. Alternatively if you lock a PLL to the frequency modulated carrier signal then your demodulated baseband signal is just whatever the instantaneous VCO control voltage give or take a phase offset Both of these should work down to DC
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.
Probably a Tek TPS2000. I would expect a pll demodulator. Not hard to do with today's ic's.
On 31.10.18 07:57, Steve Wilson wrote:
> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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. > >> Cheers > >> Phil Hobbs > > How do you get down to DC with a delay discriminator?
A ring mixer can go down to DC on its low-frequency port. When the delay is 90 degrees, the output will be zero. -- -TV
On 31.10.18 07:45, Jasen Betts wrote:
> On 2018-10-31, 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. > > SDR >
Computing arctangents at John's bandwidth will be sweaty, and it's the way to detect angle modulation (FM/PM) on a SDR. -- -TV
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.