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+- 90 phase shifter revisited

Discussion in 'Electronic Design' started by greysky, Jun 22, 2013.

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  1. greysky

    greysky Guest

    You guys had a lot of great ideas to my original post, but I realized I
    probably didn't give enough information concerning the application. In a
    block diagram, the phase shifter has 2 inputs, one is for the 1MHz sine wave
    and the other is for a control voltage, probably a ramp generated by a 16
    bit DAC. The output is the phase shifted sine wave. The ramp causes the sine
    wave to be continuously shifted up to +- 90 degrees. There will also be a
    feedback circuit which will stop the ramp at the appropriate voltage level.
    The sine is being generated by a very low noise ocxo, -110Dbc @ 1 hz from
    center, and the phase shifter needs to not mess this up. Thanks in advance
    for any ideas you may have.
     
  2. Phil Allison

    Phil Allison Guest

    "greysky"
    ** Think you need to consider a PLL used as a phase modulator.

    BTW:

    Are you the same guy trying to do weird shit using the AM band ?


    .... Phil
     
  3. Bill Sloman

    Bill Sloman Guest

    So you could use - as Phil Allison said - a voltage-controlled oscillator to produce an equally low noise 1MHz sine wave, frequency locked to the first, but phase shifted.

    Voltage-controlled crystal oscillators do exist - they use a varactor to pull the crystal frequency. The varactor can't pull it very far, so you'd need to start off with two well-matched 1MHz crystals.

    Some digital frequency synthesis chips can produce a reasonably clean pair of sine waves with any phase relationship you want to program in.

    The noise on the synthesised output will be low level high order harmonics.If your master oscillator is clean and stable, the synthesised waveforms won't have any more noise 1kHz away from the centre frequency than the divided down master oscillator frequency.

    Analog devices have lots of application notes for their - not all that cheap - DDS chips.

    http://www.analog.com/en/content/glp_dds/fca.html?gclid=CPub-tSZ97cCFQkVpQodBjwATg

    You'd have to digitise your phase-shifting voltage to get a digital number to control your phase shift, but that's no big deal.
     
  4. Greysky

    Greysky Guest

    I always thought serrodyne frequency translation took worked with
    microwave frequencies. I would think a frequency of only 1 Mhz, and
    phase translation measured in single Hz is a no-go for this method. If
    I'm wrong, I'd appreciate a link pointing me to relevant literature. Thanks.
    G-
     
  5. Greysky

    Greysky Guest

    Pretty accurate, unfortunately. It all comes down to working within
    fractions of a hertz at exactly 1 megacycle.The basic idea comes down to
    being able to make the output waveform match the frequency, waveform,
    and amplitude of an external non-connected target signal.
     
  6. miso

    miso Guest

    Pretty accurate, unfortunately. It all comes down to working within
    Given the latest revelation here, I don't think you need a phase shifter
    at all because this won't do what you want it to do. How will an ocxo
    ever match some random frequency? If there is no frequency lock, you
    will be phase shifting for ever, but you will run out of range
    eventually. Either that or I don't understand the problem. [Wouldn't be
    the first time.]

    Well at least we have a frequency.
     
  7. Greysky

    Greysky Guest

    :)

    The target frequency is known. So it is not really a matter of hunting
    for a random frequency, just matching one you already know about.
     
  8. Jamie

    Jamie Guest

    Then you need a PLL circuit.

    Jamie
     
  9. miso

    miso Guest

    Well at least we have a frequency.
    My comment was regarding the first posting of this project, where no
    frequency was given.

    Here it is again:
    "Anyone know how to make a phase shifter that will shift a sine wave +-
    90 degrees without distorting it in the process?
    Thanks."

    Is there a reason you just don't use a vxco and make a phase lock loop?
     
  10. miso

    miso Guest

    The problem is 1MHz is nominal. This requires a PLL using a vcxo. That
    design is everywhere. Colorburst lock for example. Actually locking to
    the colorburst is a harder problem.

    Even very precise telco schemes use justification bits to account for
    frequency difference.
     
  11. Phil Allison

    Phil Allison Guest

    "greysky"
    ** A troll called "George" posted here in September last year asking about
    *un-tuned* ferrite loop antennas for the AM band for a special app he
    refused to describe.

    He was very concerned about the "phase response" of the antenna.

    I think George and "greysky" are the same troll.



    .... Phil
     
  12. greysky

    greysky Guest

    "greysky" wrote in message
    You guys had a lot of great ideas to my original post, but I realized I
    probably didn't give enough information concerning the application. In a
    block diagram, the phase shifter has 2 inputs, one is for the 1MHz sine wave
    and the other is for a control voltage, probably a ramp generated by a 16
    bit DAC. The output is the phase shifted sine wave. The ramp causes the sine
    wave to be continuously shifted up to +- 90 degrees. There will also be a
    feedback circuit which will stop the ramp at the appropriate voltage level.
    The sine is being generated by a very low noise ocxo, -110Dbc @ 1 hz from
    center, and the phase shifter needs to not mess this up. Thanks in advance
    for any ideas you may have.
    +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    Again, I apologize for not describing the problem well enough. Even so,
    there are literally a ton of great ideas for me to look into, and I thank
    you all. Let me provide an overview of the problem and then maybe things'll
    be a bit clearer ( as mud, right...). This is an experiment in radio
    reception. The transmitter is an extremely low powered, unmodulated sine
    wave. Since the transmission frequency is known exactly, the receiver is
    built with fixed circuitry to specifically receive only that signal. Since
    there is no modulation (yet), the output of the mixer stage in the receiver
    is going to be the product of the phase difference between the received
    carrier and the local oscillator. I am looking for a way to manipulate the
    phase of the local oscillator to match the phase of the received carrier.
    When this happens, the phase output will be 0. I need a circuit to monitor
    the phase and change the L.O. such that it tracks the input signal and keep
    the output at 0. The lower noise, the better. Right now I am leaning towards
    a VCO scheme, but wanted to see if anyone has any better ideas. Once again,
    thanks.
     
  13. Greysky

    Greysky Guest


    Yep. :)

    Eventually I'm looking to construct a micro power radio using phase
    modulation. It seems a PLL / VCO feedback loop is still the way to go...
     
  14. miso

    miso Guest

    Also a lot of Sony portable shortwave radios have this feature. It is
    hard to do a really decent synchronous detector. The Sony radios "growl"
    at time since getting synch can cause low frequency audio. The Drake R-8
    (forget which rev) is a bit better. The AR7030 is very good. I never
    heard the Sherwood so I can't comment on it.

    Sychronous demod or lack thereof isn't a show stopper, but it is useful
    at times. Mostly if there is a strong interference, you can tune to the
    sideband furthest away.

    Most of the shortwave radio manufacturers left the business. Streaming
    put them out of business. XM used to have a cool world radio channel.
    They would switch around from DW, Radio Netherlands, etc. But they
    dropped the channel. They still have the BBC though.

    Getting the BBC on shortwave actually takes some gear these days. They
    dropped all their North American sites years ago.

    Radio Havana is worth a listen.
     
  15. Jamie

    Jamie Guest

    Today I went to the drive through at one of our local donut shops,
    when I got to the menu board I noticed the Face Book and Twitter logos. I
    know they have Wi-FI but I don't remember seeing those logos before..
    I asked the window attendant if they had camera's in the place, he said
    yes. I said oh that's just great, then I asked him if he was aware of
    facebook and twitter claiming rights to all video recorded? He didn't
    seem to know about that. Also as you know the FEDs, NSA etc have been
    using the social networks as a tool for watching people, they don't hide
    this if you read the fine print when you walk in on these eating places,
    but most people are to busy thinking about their stomach to read that
    crap and they know this.

    In any case, I told him that I will not be stopping at that location
    any more. I don't like the world watching me eat nor do I want them to
    see me driving through the pick up window. When I drove out of the lot
    I did notice a camera in the window pointing outwards at the main road
    where they can even capture non-customer cars.


    Jamie
     
  16. Just because they've got FB and Twit logos doesn't mean they're live
    streaming your mug over the internet from their security cameras.

    Those companies probably just want you to tweet about them and "like"
    them on FB, since "social media" is supposed to be the big thing.

    Just about every retail establishment has security cameras- mostly to
    watch for robberies by outside and inside perps.

    Hey, are you affected by all that H2O out there? Looks real bad from
    what I've seen. 8-(



    Best regards,
    Spehro Pefhany
     
  17. Greysky

    Greysky Guest

    Well, once the local oscillator matches the external frequency, it wont
    make sense to change that frequency. Once lock occurs, then I want to
    be able to compare the phase of the two waveforms. Wont a phase
    comparator work if the the inputs are the same frequency but out of
    phase by some amount?
     
  18. Ahh, Is the frequency known 'in theory' (like it's radio station 970 on the AM dial?) or exactly.. as in you are generating the signal bouncing it around and then detecting it again?
    (Why does this feel like twenty questions?)

    As others have said it sounds like a PLL... But you've gotta get the frequency set before worrying about the phase..

    George H.
     
  19. This all sounds so off-beat. Does the initial poster realize
    that frequency and phase are related? That the latter is the
    time integral of the former?

    Jeroen Belleman
     
  20. Bill Sloman

    Bill Sloman Guest

    You are being excessively stringent. If the phase-locked loop is fast enough to track the planned-for phase excursions, it can track larger phase excursions than +/-pi radians (or +/-180 degrees if you aren't a physicist).

    You need to have some mechanism to keep track of the more-than-one-cycle phase excursions, but that's what counters are for.

    Floyd M. Gardners's book "Phaselock techniques" talks about this at length, and what sort of tracking errors various order of phase-locked loop can be expected to show.
     
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