"Ralph A. Schmid, DK5RAS" <dk5ras@dk5ras.de> writes:> Randy Yates <yates@ieee.org> wrote: > >>Seriously, what possesses you to make such claims? Is it just a joke? >>It doesn't seem like you're joking. > > Maybe I just dod not make the point clear.Perhaps not.>>Usually people make these types of claims when they don't understand >>digital. When an analog signal is properly dithered before converting >>to digital, the result is EXACTLY the same as an analog signal in >>noise - e.g., resolution increases with narrowing bandwidth. > > I never said that was not true. The problem with digital radio > communications is, in case of fading and at the edge of the coverage > short dropouts render the signal almost unreadable in digital system, > because of the voice codec and its compression algo. Some bits are > missing, and large portions of the message can not be understood any > more.Oh, well you've gone largely off-topic then. This about demodulating an analog FM signal. In the case I'm interested in, it's a digital demodulator, but the signal itself is analog FM. But..., if the dropouts you refer to are typical and the digital signal is unreadable, then the communications engineer/signal designer didn't do their jobs right.> An anloge transmission fades out, the noise increases, and short > interruptions are not a problem, due to the redundancy of human > speech. This redundancy is what the bandwidth efficient voice codecs > use to reduce the bandwidth, and so this redundancy gets lost.But channel coding puts redundancy back in. So, as I stated above, if typical use-case scenarios severely undermine the use of the communication system, then the system designer didn't do his job correctly.> It is a fact that for example a narrowband voice channel of 12.5KHz > gives better coverage in analogue than in digital voice. Try it out!Whether narrowband or wideband, digital (done right) is always better. That is because the advantages that can be taken through the proper application of communication, information, and coding theory will always outstrip any simple analog communication technique. -- % Randy Yates % "How's life on earth? %% Fuquay-Varina, NC % ... What is it worth?" %%% 919-577-9882 % 'Mission (A World Record)', %%%% <yates@ieee.org> % *A New World Record*, ELO http://home.earthlink.net/~yatescr
FM Demodulation
Started by ●January 17, 2007
Reply by ●January 20, 20072007-01-20
Reply by ●January 20, 20072007-01-20
Randy Yates wrote:> "Ralph A. Schmid, DK5RAS" <dk5ras@dk5ras.de> writes: > >> Vladimir Vassilevsky <antispam_bogus@hotmail.com> wrote: >> >>> Yes, of course. Pretty much any good algorithm of the frequency >>> estimation can be used. It will make the FM demodulator which performs >>> better then the PLL. Also, the statistics of the audio signal can be >>> exploited... However the radical solution will be encoding the audio >>> into MP3 and transmitting it digitally. No analog solution can beat that. >> Only with strong signals, when you are getting to the edge, digital >> systems usually fail. >> >> The best FM receiver I ever have seen uses a DSP for demodulating the >> last IF; but in this radio FM is only a side effect, it is designed >> for completely digital voice transmission. In static environment >> digital and analog mode are comparable in maximum range, with better >> audi in digital mode, but in a dynamic environment digital just sucks, >> and only analog FM gives audio one can understand :) > > Them's fightin' words around here, Ralph! It's not nice to tease the > natives. > > Seriously, what possesses you to make such claims? Is it just a joke? > It doesn't seem like you're joking. > > Usually people make these types of claims when they don't understand > digital. When an analog signal is properly dithered before converting > to digital, the result is EXACTLY the same as an analog signal in > noise - e.g., resolution increases with narrowing bandwidth.We're talking noise on the carrier, Randy, not noise in the audio. I don't see how your comment applies. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●January 20, 20072007-01-20
Vladimir Vassilevsky <antispam_bogus@hotmail.com> writes:> Randy Yates wrote: > > >> Do you (or anyone else) know of other techniques that can push the >> threshold extension even further down than a PLL? > > Yes, of course. Pretty much any good algorithm of the frequency > estimation can be used. It will make the FM demodulator which performs > better then the PLL.Hi Vladimir, Your assertion sounds enticing, but I'm having a hard time going from your words to having any idea of how such an implementation would be done. Do you have an example? -- % Randy Yates % "Watching all the days go by... %% Fuquay-Varina, NC % Who are you and who am I?" %%% 919-577-9882 % 'Mission (A World Record)', %%%% <yates@ieee.org> % *A New World Record*, ELO http://home.earthlink.net/~yatescr
Reply by ●January 20, 20072007-01-20
Jerry Avins <jya@ieee.org> writes:> Randy Yates wrote: >> "Ralph A. Schmid, DK5RAS" <dk5ras@dk5ras.de> writes: >> >>> Vladimir Vassilevsky <antispam_bogus@hotmail.com> wrote: >>> >>>> Yes, of course. Pretty much any good algorithm of the frequency >>>> estimation can be used. It will make the FM demodulator which >>>> performs better then the PLL. Also, the statistics of the audio >>>> signal can be exploited... However the radical solution will be >>>> encoding the audio into MP3 and transmitting it digitally. No >>>> analog solution can beat that. >>> Only with strong signals, when you are getting to the edge, digital >>> systems usually fail. >>> >>> The best FM receiver I ever have seen uses a DSP for demodulating the >>> last IF; but in this radio FM is only a side effect, it is designed >>> for completely digital voice transmission. In static environment >>> digital and analog mode are comparable in maximum range, with better >>> audi in digital mode, but in a dynamic environment digital just sucks, >>> and only analog FM gives audio one can understand :) >> Them's fightin' words around here, Ralph! It's not nice to tease the >> natives. >> Seriously, what possesses you to make such claims? Is it just a >> joke? It doesn't seem like you're joking. >> Usually people make these types of claims when they don't understand >> digital. When an analog signal is properly dithered before converting >> to digital, the result is EXACTLY the same as an analog signal in >> noise - e.g., resolution increases with narrowing bandwidth. > > We're talking noise on the carrier, Randy, not noise in the audio. I > don't see how your comment applies.My mistake - I did not read Ralph's comment in the correct context. -- % Randy Yates % "...the answer lies within your soul %% Fuquay-Varina, NC % 'cause no one knows which side %%% 919-577-9882 % the coin will fall." %%%% <yates@ieee.org> % 'Big Wheels', *Out of the Blue*, ELO http://home.earthlink.net/~yatescr
Reply by ●January 21, 20072007-01-21
Actually most modern analog FM receivers use what is called a quadrature detector which allows the use of a single tank circuit withoiut anytaps or secondaries etc. The performance it equivalnet to a ratio det or a discriminator but is easier to implement and tune..in fact moslty they are implemented with a ceramic or crystal resonantor so no tuning is needed... And re the discussion of analog vs digital, digital may have several dB advantage in a static situation near threshold like in a space system, but for a walkie talkie etc, the digital system cliff effect causes the audio to simply stop and due to the delay it is hard to move the radio around and find the good spot and avoid the bad spot,,,,in an anlog system as many have had the experience, when the voice starts to get noisy, you move the radio a little until it is clear... in a ditigal comm system it is harder to close this human feedvback loop without a good signal quality indicator... Mark
Reply by ●January 21, 20072007-01-21
Mark wrote:> Actually most modern analog FM receivers use what is called a > quadrature detector which allows the use of a single tank circuit > withoiut anytaps or secondaries etc. The performance it equivalnet to a > ratio det or a discriminator but is easier to implement and tune..in > fact moslty they are implemented with a ceramic or crystal resonantor > so no tuning is needed...This seems to be the case. I did a quick Google for some FM radio chips, and they all seem to have gone back from PLLs to quadrature detectors.> And re the discussion of analog vs digital, digital may have several dB > advantage in a static situation near threshold like in a space system, > but for a walkie talkie etc, the digital system cliff effect causes the > audio to simply stop and due to the delay it is hard to move the radio > around and find the good spot and avoid the bad spot,,,,in an anlog > system as many have had the experience, when the voice starts to get > noisy, you move the radio a little until it is clear... in a ditigal > comm system it is harder to close this human feedvback loop without a > good signal quality indicator...Well, I guess that's why all the cellular systems have changed from digital to analogue, and seen such a huge improvement in their quality of service. :-) Steve
Reply by ●January 21, 20072007-01-21
Steve Underwood wrote:> Mark wrote: > > Actually most modern analog FM receivers use what is called a > > quadrature detector which allows the use of a single tank circuit > > withoiut anytaps or secondaries etc. The performance it equivalnet to a > > ratio det or a discriminator but is easier to implement and tune..in > > fact moslty they are implemented with a ceramic or crystal resonantor > > so no tuning is needed... > > This seems to be the case. I did a quick Google for some FM radio chips, > and they all seem to have gone back from PLLs to quadrature detectors. > > > And re the discussion of analog vs digital, digital may have several dB > > advantage in a static situation near threshold like in a space system, > > but for a walkie talkie etc, the digital system cliff effect causes the > > audio to simply stop and due to the delay it is hard to move the radio > > around and find the good spot and avoid the bad spot,,,,in an anlog > > system as many have had the experience, when the voice starts to get > > noisy, you move the radio a little until it is clear... in a ditigal > > comm system it is harder to close this human feedvback loop without a > > good signal quality indicator... > > Well, I guess that's why all the cellular systems have changed from > digital to analogue, and seen such a huge improvement in their quality > of service. :-) > > SteveFunny, its about money, the carriers can get more users on a given bandwidth with digital, the portable phone transmitters can use less power so the batteries last longer, digital does have some advantages for cell phones... but if you are ever in a weak signal situation and need to move the radio around to find a hot spot that works, its much easier to do with an analog link... Mark
Reply by ●January 21, 20072007-01-21
"Mark" <makolber@yahoo.com> writes:> [...] > And re the discussion of analog vs digital, digital may have several dB > advantage in a static situation near threshold like in a space system, > but for a walkie talkie etc, the digital system cliff effect causes the > audio to simply stopThat's true, but the edge of digital's cliff is quite a bit further away than the bottom of analog's hill. -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Shangri-La', *A New World Record*, ELO http://home.earthlink.net/~yatescr
Reply by ●January 21, 20072007-01-21
Mark wrote:> Actually most modern analog FM receivers use what is called a > quadrature detector which allows the use of a single tank circuit > withoiut anytaps or secondaries etc. The performance it equivalnet to a > ratio det or a discriminator but is easier to implement and tune..in > fact moslty they are implemented with a ceramic or crystal resonantor > so no tuning is needed...My cousin Jack invented that for use in TV receivers, back when they still used tubes. I had audio trouble with my set and a schematic with this weird (at that time) circuit that had to be the intercarrier sound detector. IF fed the control grid, a tank circuit hung on the screen grid, and audio seemed to come out of the plate. I sort of doped it out and thought of it as a flywheel detector. the tank gets going at the average carrier frequency in quadrature with the drive; that was the flywheel. The amount of DC that gets through is determined by the phase difference between the carrier and the tank, and viola! Audio! I figured Jack was the FM expert, so I went over to his house and asked him about the weird circuit. He took umbrage at the adjective, but seemed pleased that I had analyzed it correctly without using math. "You make it seem simple. I worked on those equations for a week." is how I found out it was his design. (I once explained to him without even waving my arms how phase-contrast microscopy works. It's that simple too.) ... Jerry P.S. Everybody knows the Foster-Seely discriminator. Somehow, "Avins-Seely" didn't stick to "ratio detector". Jack's first patent was the VTVM. -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●January 21, 20072007-01-21
Randy Yates wrote:> "Mark" <makolber@yahoo.com> writes: >> [...] >> And re the discussion of analog vs digital, digital may have several dB >> advantage in a static situation near threshold like in a space system, >> but for a walkie talkie etc, the digital system cliff effect causes the >> audio to simply stop > > That's true, but the edge of digital's cliff is quite a bit further > away than the bottom of analog's hill.That's not always a good trade. Riggers prefer a chain that yields at five tons and breaks at seven to one that snaps at ten without warning. Digital systems may be stronger, but they're brittle. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
