Hello, As I understand it, phase/frequency modulation is usually achieved by generating by directly modifying the argument of a sinusoid. However, if the task was to frequency modulate an existing signal which itself we don't generate, is there a standard way doing so, e.g. by superposing a modulating signal (probably a piecewise continuous signal) on the existing signal? In my case, phase modulation might be the more proper term. Thanks in advance!
Generating phase modulation.
Started by ●December 7, 2009
Reply by ●December 7, 20092009-12-07
Demus <sodemus@hotmail.com> wrote:>Hello,>As I understand it, phase/frequency modulation is usually achieved by >generating by directly modifying the argument of a sinusoid.>However, if the task was to frequency modulate an existing signal which >itself we don't generate, is there a standard way doing so, e.g. by >superposing a modulating signal (probably a piecewise continuous signal) on >the existing signal?You can feed an existing carrier into an balanced modulator and modulate it with a complex baseband signal containing all the desired components and sidebands of the target frequency-modulated signal. Or in some cases, you can lock onto the existing carrier and frequency-modulate a replica of it. Steve
Reply by ●December 7, 20092009-12-07
Demus wrote:> Hello, > > As I understand it, phase/frequency modulation is usually achieved by > generating by directly modifying the argument of a sinusoid. > > However, if the task was to frequency modulate an existing signal which > itself we don't generate, is there a standard way doing so, e.g. by > superposing a modulating signal (probably a piecewise continuous signal) on > the existing signal? > > In my case, phase modulation might be the more proper term.There is 1001 method for doing that, depending on what is available and how deep and how accurate should be the modulation. Perhaps the simplest is passing the signal through variable phase shifter. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●December 7, 20092009-12-07
>Demus <sodemus@hotmail.com> wrote: > >>Hello, > >>As I understand it, phase/frequency modulation is usually achieved by >>generating by directly modifying the argument of a sinusoid. > >>However, if the task was to frequency modulate an existing signal which >>itself we don't generate, is there a standard way doing so, e.g. by >>superposing a modulating signal (probably a piecewise continuous signal)on>>the existing signal? > >You can feed an existing carrier into an balanced modulator and modulate >it with a complex baseband signal containing all the desired components >and sidebands of the target frequency-modulated signal. > >Or in some cases, you can lock onto the existing carrier and >frequency-modulate a replica of it. > >Steve >Thanks for your swift reply! Ok, so if I have a signal consisting of let's say 100 sinusoids, is there then a way to adjust their respective phases so that their instantaneous phases match a prescribed set of phases at a particular time instant? Can this be done with the balanced modulator you mentioned above? In that case, do you have any particular place you can recommend for reading about this?
Reply by ●December 7, 20092009-12-07
Vladimir Vassilevsky wrote:> > > Demus wrote: > >> Hello, >> >> As I understand it, phase/frequency modulation is usually achieved by >> generating by directly modifying the argument of a sinusoid. >> >> However, if the task was to frequency modulate an existing signal which >> itself we don't generate, is there a standard way doing so, e.g. by >> superposing a modulating signal (probably a piecewise continuous >> signal) on >> the existing signal? >> In my case, phase modulation might be the more proper term. > > There is 1001 method for doing that, depending on what is available and > how deep and how accurate should be the modulation. Perhaps the simplest > is passing the signal through variable phase shifter.One night in 1951, I had worked late on the CCNY ham transmitter, W2HJ, when I found that I was locked into the building. I had the modulator apart and I didn't know Morse well enough to trust keying the final, so I soldered tin can bottoms to adjacent turns of the output tank. The final was a an Eimac 304TH with a KW input, so getting too close would have zapped me good. I arranges a piece of grounded screen wire between me and the improvised capacitor plates and shouted, The resulting phase modulation was enough to get through to a kind soul who phoned the police who, in turn, got Buildings and Grounds to let me out. I had no ticket, but nobody blinked when I used the station's call letters. A slope detector is frequency sensitive, so a phase modulator comes through with a 6 dB/octave slope, but it's still intelligible. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 7, 20092009-12-07
> >There is 1001 method for doing that, depending on what is available and >how deep and how accurate should be the modulation. Perhaps the simplest>is passing the signal through variable phase shifter. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com > >Thanks for your reply, I didn't find anything online about variable phase shifters. Are they usually implemented as a variable all-pass filter? Do you know of any references I can turn to?
Reply by ●December 7, 20092009-12-07
Demus wrote:>> Demus <sodemus@hotmail.com> wrote: >> >>> Hello, >>> As I understand it, phase/frequency modulation is usually achieved by >>> generating by directly modifying the argument of a sinusoid. >>> However, if the task was to frequency modulate an existing signal which >>> itself we don't generate, is there a standard way doing so, e.g. by >>> superposing a modulating signal (probably a piecewise continuous signal) > on >>> the existing signal? >> You can feed an existing carrier into an balanced modulator and modulate >> it with a complex baseband signal containing all the desired components >> and sidebands of the target frequency-modulated signal. >> >> Or in some cases, you can lock onto the existing carrier and >> frequency-modulate a replica of it. >> >> Steve >> > Thanks for your swift reply! Ok, so if I have a signal consisting of let's > say 100 sinusoids, is there then a way to adjust their respective phases so > that their instantaneous phases match a prescribed set of phases at a > particular time instant? Can this be done with the balanced modulator you > mentioned above? In that case, do you have any particular place you can > recommend for reading about this?Do I understand correctly that you want to shift the phase of individual sinusoids sepatately? Is each one constant? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 7, 20092009-12-07
>Demus wrote: >>> Demus <sodemus@hotmail.com> wrote: >>> >>>> Hello, >>>> As I understand it, phase/frequency modulation is usually achievedby>>>> generating by directly modifying the argument of a sinusoid. >>>> However, if the task was to frequency modulate an existing signalwhich>>>> itself we don't generate, is there a standard way doing so, e.g. by >>>> superposing a modulating signal (probably a piecewise continuoussignal)>> on >>>> the existing signal? >>> You can feed an existing carrier into an balanced modulator andmodulate>>> it with a complex baseband signal containing all the desiredcomponents>>> and sidebands of the target frequency-modulated signal. >>> >>> Or in some cases, you can lock onto the existing carrier and >>> frequency-modulate a replica of it. >>> >>> Steve >>> >> Thanks for your swift reply! Ok, so if I have a signal consisting oflet's>> say 100 sinusoids, is there then a way to adjust their respectivephases so>> that their instantaneous phases match a prescribed set of phases at a >> particular time instant? Can this be done with the balanced modulatoryou>> mentioned above? In that case, do you have any particular place youcan>> recommend for reading about this? > >Do I understand correctly that you want to shift the phase of individual>sinusoids sepatately? Is each one constant? > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >Yes, each sinusoid separately. And constant... I guess I'm not sure what you mean but the sinusoids are just (presumably) stationary sinusoids described by a DFT. Am I sensing a upcoming mockery? =) Perhaps I'm going about this the wrong way altogether, the chirplet transform have crossed my mind and might be more appropriate. The DFT might just be computationally more appealing.
Reply by ●December 7, 20092009-12-07
Reply by ●December 7, 20092009-12-07
Demus wrote: ... I wrote:>> Do I understand correctly that you want to shift the phase of individual > >> sinusoids sepatately? Is each one constant?> Yes, each sinusoid separately. And constant... I guess I'm not sure what > you mean but the sinusoids are just (presumably) stationary sinusoids > described by a DFT. Am I sensing a upcoming mockery? =)Not at all. Puzzlement, perhaps.> Perhaps I'm going about this the wrong way altogether, the chirplet > transform have crossed my mind and might be more appropriate. The DFT might > just be computationally more appealing.I'm not sure what "it" is. You have a bunch of sinusoids whose phase you want to adjust individually. Neither their frequencies nor their amplitudes, nor their phases relative to some reference change with time. Why not build a network for each frequency that alters its phase to your liking? If it affects amplitude, you can restore that with a multiplicative constant. That's simple enough so that I'm puzzled that you ask. If it's not that, I'm puzzled about what you want. Note that phase is defined only for frequencies that are exactly equal. Although we use the term loosely in other contexts, the meaning has to be explicitly defined for each context. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
