HardySpicer wrote: ...> Phase modulation is just FM but without the integrator on the > baseband.That's one way to look at it. You might say that frequency modulation is just PM without the differentiator in the baseband. Both statements are based on unwarranted assumptions. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Generating phase modulation.
Started by ●December 7, 2009
Reply by ●December 8, 20092009-12-08
Reply by ●December 9, 20092009-12-09
On Dec 9, 9:23�am, Jerry Avins <j...@ieee.org> wrote:> HardySpicer wrote: > > � �... > > > Phase modulation is just FM but without the integrator on the > > baseband. > > That's one way to look at it. You might say that frequency modulation is > just PM without the differentiator in the baseband. Both statements are > based on unwarranted assumptions. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Interesting to note that when we apply emphasis-de-emphasis that these circuits are integrator/differentiator types.(over a limited freq band ie +/- 20dB/decade slopes) Therefore at transmission we transmit FM and reception PM! Hardy
Reply by ●December 9, 20092009-12-09
HardySpicer wrote:> On Dec 9, 9:23 am, Jerry Avins <j...@ieee.org> wrote: >> HardySpicer wrote: >> >> ... >> >>> Phase modulation is just FM but without the integrator on the >>> baseband. >> That's one way to look at it. You might say that frequency modulation is >> just PM without the differentiator in the baseband. Both statements are >> based on unwarranted assumptions. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Interesting to note that when we apply emphasis-de-emphasis that these > circuits are integrator/differentiator types.(over a limited freq band > ie +/- 20dB/decade slopes) > Therefore at transmission we transmit FM and reception PM!Since preemphasis is applied only to the upper part of the audio spectrum, you can say that what is broadcast is partly FM and partly PM. It is often far easier to describe things than to categorize them. Loki knew that when he insisted "All of my head and none of my neck!" Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 9, 20092009-12-09
>On Dec 9, 9:23=A0am, Jerry Avins <j...@ieee.org> wrote: >> HardySpicer wrote: >> >> =A0 =A0... >> >> > Phase modulation is just FM but without the integrator on the >> > baseband. >> >> That's one way to look at it. You might say that frequency modulationis>> just PM without the differentiator in the baseband. Both statementsare>> based on unwarranted assumptions. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you canget.>>=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=>=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= >=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF > >Interesting to note that when we apply emphasis-de-emphasis that these >circuits are integrator/differentiator types.(over a limited freq band >ie +/- 20dB/decade slopes) >Therefore at transmission we transmit FM and reception PM!Its only really frequency modulation when the baseband goes down to DC (e.g. FSK). Without the DC component the long term number of cycles of the signal must equate to the cycles of the carrier over the same period, so you are only really juggling the phase. Steve
Reply by ●December 9, 20092009-12-09
steveu wrote:>> On Dec 9, 9:23=A0am, Jerry Avins <j...@ieee.org> wrote: >>> HardySpicer wrote: >>> >>> =A0 =A0... >>> >>>> Phase modulation is just FM but without the integrator on the >>>> baseband. >>> That's one way to look at it. You might say that frequency modulation > is >>> just PM without the differentiator in the baseband. Both statements > are >>> based on unwarranted assumptions. >>> >> >> Interesting to note that when we apply emphasis-de-emphasis that these >> circuits are integrator/differentiator types.(over a limited freq band >> ie +/- 20dB/decade slopes) >> Therefore at transmission we transmit FM and reception PM! > > Its only really frequency modulation when the baseband goes down to DC > (e.g. FSK). Without the DC component the long term number of cycles of the > signal must equate to the cycles of the carrier over the same period, so > you are only really juggling the phase.How low must the modulating frequency go to qualify as FM? one cycle/min? /hour? /day? /year? Suppose there was an FM-capable system, but the modulation was (in this case) capacitively coupled? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 9, 20092009-12-09
>steveu wrote: >>> On Dec 9, 9:23=A0am, Jerry Avins <j...@ieee.org> wrote: >>>> HardySpicer wrote: >>>> >>>> =A0 =A0... >>>> >>>>> Phase modulation is just FM but without the integrator on the >>>>> baseband. >>>> That's one way to look at it. You might say that frequencymodulation>> is >>>> just PM without the differentiator in the baseband. Both statements >> are >>>> based on unwarranted assumptions. >>>> >>> >>> Interesting to note that when we apply emphasis-de-emphasis thatthese>>> circuits are integrator/differentiator types.(over a limited freqband>>> ie +/- 20dB/decade slopes) >>> Therefore at transmission we transmit FM and reception PM! >> >> Its only really frequency modulation when the baseband goes down to DC >> (e.g. FSK). Without the DC component the long term number of cycles ofthe>> signal must equate to the cycles of the carrier over the same period,so>> you are only really juggling the phase. > >How low must the modulating frequency go to qualify as FM? one >cycle/min? /hour? /day? /year? Suppose there was an FM-capable system, >but the modulation was (in this case) capacitively coupled?Even most FSK transmitters were capacitively coupled until the end of the 80s. Most early paging transmitters, for example. Most paging receivers (in what remains of that industry) are still capacitively coupled. Clean DC capable FM transmitters had to wait until DSP based modulators become economically viable. Its all a horrible fudge, and it does cost in performance, as the codes make to attempt to approach DC balance. Steve
Reply by ●December 10, 20092009-12-10
steveu wrote:> Even most FSK transmitters were capacitively coupled until the end of the > 80s. Most early paging transmitters, for example. Most paging receivers (in > what remains of that industry) are still capacitively coupled. Clean DC > capable FM transmitters had to wait until DSP based modulators become > economically viable. Its all a horrible fudge, and it does cost in > performance, as the codes make to attempt to approach DC balance.Early paging transmitters used direct DC coupled modulation of the crystal, which was multiplied and frequency shifted then. Synthesized transmitters used to modulate both reference crystal (DC coupled) and VCO (AC coupled); there was special adjustment to match deviations. The performance was indeed affected by that adjustment. If a frequency standard was used as a reference, which was impossible to modulate directly, I did forward/backward phase rotation using 7486, 7404 and 7474. PLL smoothed phase jerks :)))) That was before DSPs. On the receive side, big problem was DC offset due to carrier frequency mismatch and discriminator zero drift. The receiver had to be AC coupled to cancel that offset. Good cure for lost DC was Schmitt comparator at the input. In POCSAG/FLEX/ERMES, there was no attempt to make codes DC-balanced. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●December 10, 20092009-12-10
> > >steveu wrote: > > >> Even most FSK transmitters were capacitively coupled until the end ofthe>> 80s. Most early paging transmitters, for example. Most paging receivers(in>> what remains of that industry) are still capacitively coupled. CleanDC>> capable FM transmitters had to wait until DSP based modulators become >> economically viable. Its all a horrible fudge, and it does cost in >> performance, as the codes make to attempt to approach DC balance. > >Early paging transmitters used direct DC coupled modulation of the >crystal, which was multiplied and frequency shifted then. Synthesized >transmitters used to modulate both reference crystal (DC coupled) and >VCO (AC coupled); there was special adjustment to match deviations. The >performance was indeed affected by that adjustment. >If a frequency standard was used as a reference, which was impossible to>modulate directly, I did forward/backward phase rotation using 7486, >7404 and 7474. PLL smoothed phase jerks :)))) That was before DSPs. >On the receive side, big problem was DC offset due to carrier frequency >mismatch and discriminator zero drift. The receiver had to be AC coupled>to cancel that offset. Good cure for lost DC was Schmitt comparator at >the input. >In POCSAG/FLEX/ERMES, there was no attempt to make codes DC-balanced. > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.comSome POCSAG transmitters with ovenised references used a variety of tricks to get DC modulation, but usually with a variety of side effects. People did things like switching the n or m value in an n/m PLL, which had horrible side effects. Most transmitters, including some major brands, made no attempt at DC modulation at all. The first totally clean modulation I ever saw from a paging transmitter was the from the first one with a DSP modulator. Steve
Reply by ●December 10, 20092009-12-10
steveu wrote:>> >>steveu wrote: >> >> >> >>>Even most FSK transmitters were capacitively coupled until the end of > > the > >>>80s. Most early paging transmitters, for example. Most paging receivers > > (in > >>>what remains of that industry) are still capacitively coupled. Clean > > DC > >>>capable FM transmitters had to wait until DSP based modulators become >>>economically viable. Its all a horrible fudge, and it does cost in >>>performance, as the codes make to attempt to approach DC balance. >> >>Early paging transmitters used direct DC coupled modulation of the >>crystal, which was multiplied and frequency shifted then. Synthesized >>transmitters used to modulate both reference crystal (DC coupled) and >>VCO (AC coupled); there was special adjustment to match deviations. The >>performance was indeed affected by that adjustment. >>If a frequency standard was used as a reference, which was impossible to > > >>modulate directly, I did forward/backward phase rotation using 7486, >>7404 and 7474. PLL smoothed phase jerks :)))) That was before DSPs. >>On the receive side, big problem was DC offset due to carrier frequency >>mismatch and discriminator zero drift. The receiver had to be AC coupled > > >>to cancel that offset. Good cure for lost DC was Schmitt comparator at >>the input. >>In POCSAG/FLEX/ERMES, there was no attempt to make codes DC-balanced. >> > > Some POCSAG transmitters with ovenised references used a variety of tricks > to get DC modulation, but usually with a variety of side effects. People > did things like switching the n or m value in an n/m PLL, which had > horrible side effects.The PLL will be kicked out of lock, followed by nasty reacquisition process. When I designed paging transmitters, I dropped this idea.> Most transmitters, including some major brands, made > no attempt at DC modulation at all. The first totally clean modulation I > ever saw from a paging transmitter was the from the first one with a DSP > modulator.Yes, DSP modulation looks very nice; however the problem with DSP are different digital residuals showing up as out of band emmissions. BTW, AD makes DDS chips which can generate linear frequency ramps by themselves. I often have a sad feeling that with the technology of today it is possible to do a lot of things finally in the right way; like, say, optimal FM receivers. However, modern technologies are mainly used to breed idiotic monstrous solutions, like 8-VSB, Windows Vista, LTE, DAB, etc. which are nothing but a waste of resources. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●December 10, 20092009-12-10
> > >steveu wrote: > >>> >>>steveu wrote: >>> >>> >>> >>>>Even most FSK transmitters were capacitively coupled until the end of >> >> the >> >>>>80s. Most early paging transmitters, for example. Most pagingreceivers>> >> (in >> >>>>what remains of that industry) are still capacitively coupled. Clean >> >> DC >> >>>>capable FM transmitters had to wait until DSP based modulators become >>>>economically viable. Its all a horrible fudge, and it does cost in >>>>performance, as the codes make to attempt to approach DC balance. >>> >>>Early paging transmitters used direct DC coupled modulation of the >>>crystal, which was multiplied and frequency shifted then. Synthesized >>>transmitters used to modulate both reference crystal (DC coupled) and >>>VCO (AC coupled); there was special adjustment to match deviations. The>>>performance was indeed affected by that adjustment. >>>If a frequency standard was used as a reference, which was impossibleto>> >> >>>modulate directly, I did forward/backward phase rotation using 7486, >>>7404 and 7474. PLL smoothed phase jerks :)))) That was before DSPs. >>>On the receive side, big problem was DC offset due to carrier frequency>>>mismatch and discriminator zero drift. The receiver had to be ACcoupled>> >> >>>to cancel that offset. Good cure for lost DC was Schmitt comparator at>>>the input. >>>In POCSAG/FLEX/ERMES, there was no attempt to make codes DC-balanced. >>> >> >> Some POCSAG transmitters with ovenised references used a variety oftricks>> to get DC modulation, but usually with a variety of side effects.People>> did things like switching the n or m value in an n/m PLL, which had >> horrible side effects. > >The PLL will be kicked out of lock, followed by nasty reacquisition >process. When I designed paging transmitters, I dropped this idea.Wow! What did you do to make it that bad? That isn't the real problem. The real problem is the bias caused by the different loop update time between n/m having n set x and to x + 1. This makes the thing sensitive to the bit pattern, with significant wavering of the carrier frequency with specific patterns.>> Most transmitters, including some major brands, made >> no attempt at DC modulation at all. The first totally clean modulationI>> ever saw from a paging transmitter was the from the first one with aDSP>> modulator. > >Yes, DSP modulation looks very nice; however the problem with DSP are >different digital residuals showing up as out of band emmissions.Sure. Various intermod related mess is always a pain with digital modulation.>BTW, AD makes DDS chips which can generate linear frequency ramps by >themselves. I often have a sad feeling that with the technology of today>it is possible to do a lot of things finally in the right way; like, >say, optimal FM receivers. However, modern technologies are mainly used >to breed idiotic monstrous solutions, like 8-VSB, Windows Vista, LTE, >DAB, etc. which are nothing but a waste of resources.Regards, Steve
