steveu wrote:> 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.The m/n is essentially open loop gain. The x/x+1 variation would be 1e-4 or even less then that. Why would such small variation of the open loop gain cause significant wavering of the carrier? VLV
Generating phase modulation.
Started by ●December 7, 2009
Reply by ●December 10, 20092009-12-10
Reply by ●December 10, 20092009-12-10
> > >steveu wrote: > >> 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 timebetween>> n/m having n set x and to x + 1. This makes the thing sensitive to thebit>> pattern, with significant wavering of the carrier frequency withspecific>> patterns. > >The m/n is essentially open loop gain. The x/x+1 variation would be >1e-4 or even less then that. Why would such small variation of the open >loop gain cause significant wavering of the carrier?That sounds just like the kind of argument that lead to the funky designs I had to sort out about 20 years ago. :-) Steve
Reply by ●December 11, 20092009-12-11
On Dec 10, 1:30�pm, "steveu" <ste...@coppice.org> 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. > > >> Jerry > >> -- > >> Engineering is the art of making what you want from things you can > get. > > =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. > > SteveYes by the textbooks. This is a bit like looking at an op-amp without feedback. Is it a pure integrator? Well it is flat up to maybe 20Hz before it drops off. Is that an integrator? Hardy
Reply by ●December 11, 20092009-12-11
Wow, I thought this thread had died out. Sorry I didn't keep up with it. So, to the original question, what methods can I use if I want to implement this digitally? I guess what it ends up being is a time varying filterbank, with the filterbank interpretation of the DFT... Any thoughts?
Reply by ●December 11, 20092009-12-11
Demus wrote:> Wow, I thought this thread had died out. Sorry I didn't keep up with it. > So, to the original question, what methods can I use if I want to implement > this digitally? I guess what it ends up being is a time varying filterbank, > with the filterbank interpretation of the DFT... > > Any thoughts?Split the carrier into I and Q components (sine and cosine, or two copies at 90 degrees phase difference). Multiply one component with sine of the desired modulation angle and the other with cosine of the desired modulation angle, add results together. Math is left as homework. For frequency modulation, step the modulation angle by a constant at each sample. Math is part 2 of homework. -- Tauno Voipio tauno voipio (at) iki fi
Reply by ●December 11, 20092009-12-11
> 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 VassilevskyThis is so true in the 2 way radio field. With todays IC's we could make really reliable, small, low power, agile FM transcievers...but no instead the industry has adopted digital modulation and the result is bigger heavier much more complex radios that provide less reliable communications. Its all about the $ Mark
Reply by ●December 12, 20092009-12-12
On 12/11/2009 7:17 PM, Mark wrote:>> 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 > > This is so true in the 2 way radio field. With todays IC's we could > make really reliable, small, low power, agile FM transcievers...but > no instead the industry has adopted digital modulation and the result > is bigger heavier much more complex radios that provide less reliable > communications. Its all about the $ > > MarkI wouldn't go that far. There's a difference between understanding different modulations and their capabilities and building some monstrosity out of them. How does one transmit digital data without using a digital modulation? PSK and QAM have better capacities than comparable FSK modulations, or did you mean something different? -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
Reply by ●December 12, 20092009-12-12
Eric Jacobsen wrote:> On 12/11/2009 7:17 PM, Mark wrote: > >>> 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 >> >> >> This is so true in the 2 way radio field. With todays IC's we could >> make really reliable, small, low power, agile FM transcievers...but >> no instead the industry has adopted digital modulation and the result >> is bigger heavier much more complex radios that provide less reliable >> communications. Its all about the $ >> >> Mark > > > I wouldn't go that far. There's a difference between understanding > different modulations and their capabilities and building some > monstrosity out of them. How does one transmit digital data without > using a digital modulation? PSK and QAM have better capacities than > comparable FSK modulations, or did you mean something different?I think it is about DMR vs conventional analog FM 2-way radio. Mark has a point. BTW, trivial 800MHz analog cordless phone works better and has several times of battery life compared to those spread spectrum things. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●December 12, 20092009-12-12
On 12/11/2009 10:59 PM, Vladimir Vassilevsky wrote:> > > Eric Jacobsen wrote: > >> On 12/11/2009 7:17 PM, Mark wrote: >> >>>> 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 >>> >>> >>> This is so true in the 2 way radio field. With todays IC's we could >>> make really reliable, small, low power, agile FM transcievers...but >>> no instead the industry has adopted digital modulation and the result >>> is bigger heavier much more complex radios that provide less reliable >>> communications. Its all about the $ >>> >>> Mark >> >> >> I wouldn't go that far. There's a difference between understanding >> different modulations and their capabilities and building some >> monstrosity out of them. How does one transmit digital data without >> using a digital modulation? PSK and QAM have better capacities than >> comparable FSK modulations, or did you mean something different? > > I think it is about DMR vs conventional analog FM 2-way radio. Mark has > a point. BTW, trivial 800MHz analog cordless phone works better and has > several times of battery life compared to those spread spectrum things. > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultant > http://www.abvolt.comThere's no question the electronics required to do analog FM are far simpler and more power efficient than most digital systems. As far as squeezing the most performance out of the signal for the transmitted power level, though, you'll always be better off with a well-engineered digital system than the most efficient FM system. When it comes down to analog voice and the ability of a human to pick out information in a noisy or weak signal, though, it becomes too subjective to compare. The brain does have a really good decoder for human speech (usually), and that may help a link work in some places where a digital system might lose lock. But for transporting bits, I don't there's much contest. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
Reply by ●December 12, 20092009-12-12
Eric Jacobsen wrote:> On 12/11/2009 10:59 PM, Vladimir Vassilevsky wrote: >> >> >> Eric Jacobsen wrote: >> >>> On 12/11/2009 7:17 PM, Mark wrote: >>> >>>>> 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 >>>> >>>> >>>> This is so true in the 2 way radio field. With todays IC's we could >>>> make really reliable, small, low power, agile FM transcievers...but >>>> no instead the industry has adopted digital modulation and the result >>>> is bigger heavier much more complex radios that provide less reliable >>>> communications. Its all about the $ >>>> >>>> Mark >>> >>> >>> I wouldn't go that far. There's a difference between understanding >>> different modulations and their capabilities and building some >>> monstrosity out of them. How does one transmit digital data without >>> using a digital modulation? PSK and QAM have better capacities than >>> comparable FSK modulations, or did you mean something different? >> >> I think it is about DMR vs conventional analog FM 2-way radio. Mark has >> a point. BTW, trivial 800MHz analog cordless phone works better and has >> several times of battery life compared to those spread spectrum things. >> >> Vladimir Vassilevsky >> DSP and Mixed Signal Design Consultant >> http://www.abvolt.com > > There's no question the electronics required to do analog FM are far > simpler and more power efficient than most digital systems. As far as > squeezing the most performance out of the signal for the transmitted > power level, though, you'll always be better off with a well-engineered > digital system than the most efficient FM system. > > When it comes down to analog voice and the ability of a human to pick > out information in a noisy or weak signal, though, it becomes too > subjective to compare. The brain does have a really good decoder for > human speech (usually), and that may help a link work in some places > where a digital system might lose lock. > > But for transporting bits, I don't there's much contest.Digital comms may be too good. There's no gradual degradation; they're either perfect or they quit, usually without warning. Low SNR digital TV breaks up or freezes where analog TV would be full of snow but usable. IIRC,at least one urban fire department went back to analog walkie-talkies. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
