On 2021-06-06, Cursitor Doom <cd@nowhere.com> wrote:> On Sun, 6 Jun 2021 04:26:51 -0700 (PDT), Bill Sloman ><bill.sloman@ieee.org> wrote: > >>On Sunday, June 6, 2021 at 6:47:00 PM UTC+10, Cursitor Doom wrote: >>> On Sat, 5 Jun 2021 17:33:52 -0700 (PDT), Harry Dudley-Bestow >>> <harry.dud...@gmail.com> wrote: >>> >>> >On Saturday, June 5, 2021 at 5:26:32 PM UTC-7, palli...@gmail.com wrote: >>> >> harry.dud...@gmail.com wrote: >>> >> ========================== >>> >> > Looking to build a sensible FM radio transmit/receive pair, designed for short range (10s of meters) and excellent audio quality. >>> >> >>> >> ** Just one system ? Mono or stereo ? AC or battery powered ? >>> >> > Making for personal use, so very flexible on operating frequency, BOM cost etc. >>> >> ** You are are aware of wireless mic systems for musical performances ? >>> >> Most are variable frequency, wide band FM with "twin diversity" receivers on UHF. >>> >> The latter is very important as single receivers work poorly indoors due to standing wave self cancellations. >>> >> >>> >> Building your own one sounds absurd >>> >> >>> >Phil: >>> >I just want to build one system. I know some FM use a difference signal for stereo but that sounds too complicated for my first project, so I'll just build two systems and operate them of different bands for L/R. The system will be USB powered on the transmit side, and battery powered on the receive side (I'll drill a hole in my headphones and tap off the battery). >>> > >>> >You are of course correct that it is absurd to build my own setup if the goal is to just get a working setup. But this is a learning project and so the journey is the important thing, not the destination! I will look into 'twin diversity' receivers for FM radio. Do you think I could avoid standing wave problems if I just occupied a huge bandwidth (say the whole 902-928MHz band)? >>> >>> Alison knows sweet FA about RF and is one of the biggest trolls on this group - as yu'll find out if you continue your exchange with him. Just thought I'd give you a heads-up on that little fact. >> >>Cursitor Doom knows very little about anything, but he's just as ill-informed about the depth of his ignorance as he is about everything else. >> >>He's also an even worse troll than Phil Alison - mainly because Phil Alison knows quite a bit audio (which does include FM radio) and devotes some of his tine to telling people about it. >> >>Cursitor Doom's "heads up" is just one more reminder that Cursitor Doom's head is firmly up his own backside. > > The three worst trolls on this newsgroup are Bill Sloman (by some > margin) followed by Phil Alison and Destitutedrugabuser. I believe > they all come from Sydney, which no doubt goes a long way to > accounting for this phenomenon; Sydney's lingua franca being > outstanding in the English-speaking world for it's unashamed > courseness. There's not a lot to be said in favour of the rest of the > country, either, if the truth be told, but the Sydneyites are a > special breed indeed when it comes to getting attention by *any* > means.That can't possibly be true. John Doe says I am the greatest troll. -- Jasen.
FM radio design resources
Started by ●June 5, 2021
Reply by ●June 6, 20212021-06-06
Reply by ●June 6, 20212021-06-06
On 2021-06-06, Cursitor Doom <cd@nowhere.com> wrote:> On Sun, 6 Jun 2021 08:14:43 -0700 (PDT), Bill Sloman ><bill.sloman@ieee.org> wrote: > >>On Sunday, June 6, 2021 at 11:58:35 PM UTC+10, Cursitor Doom wrote: >>> On Sun, 6 Jun 2021 04:26:51 -0700 (PDT), Bill Sloman >>> <bill....@ieee.org> wrote: >>> >>> >On Sunday, June 6, 2021 at 6:47:00 PM UTC+10, Cursitor Doom wrote: >>> >> On Sat, 5 Jun 2021 17:33:52 -0700 (PDT), Harry Dudley-Bestow >>> >> <harry.dud...@gmail.com> wrote: >>> >> >>> >> >On Saturday, June 5, 2021 at 5:26:32 PM UTC-7, palli...@gmail.com wrote: >>> >> >> harry.dud...@gmail.com wrote: >> >><snip> >> >>> >Cursitor Doom knows very little about anything, but he's just as ill-informed about the depth of his ignorance as he is about everything else. >>> > >>> >He's also an even worse troll than Phil Alison - mainly because Phil Alison knows quite a bit audio (which does include FM radio) and devotes some of his tine to telling people about it. >>> > >>> >Cursitor Doom's "heads up" is just one more reminder that Cursitor Doom's head is firmly up his own backside. >>> >>> The three worst trolls on this newsgroup are Bill Sloman (by some margin) followed by Phil Alison and Destitutedrugabuser. I believe they all come from Sydney, which no doubt goes a long way to accounting for this phenomenon; Sydney's lingua franca being outstanding in the English-speaking world for it's unashamed >>> courseness. >> >>Cursitor Doom is wrong a lot of the time. He's probably not the worst troll here - John Doe is even worse, and Flyguy isn't far behind. Nobody else is in the hunt. >> >>I'm not from Sydney - I might live in Sydney now, but I was born northern Tasmania, went to university in Melbourne, then spent 22 years in the UK and 19 more in the Netherlands. Decadent Linux User Numero Uno is an American - as is obvious to everybody except Cursitor Doom. >> >>I can't say that I've noticed that Sydney's lingua franca is particularly coarse - I do hang around with university professors and the like, so I might not hear the same sort of language that Cursitor Doom would if he visited here to further his criminal interests. >> >>> There's not a lot to be said in favour of the rest of the country, either, if the truth be told, but the Sydneyites are a special breed indeed when it comes to getting attention by *any* means. >> >>Queensland is worse. Look at Clive Palmer. >> >>https://en.wikipedia.org/wiki/Clive_Palmer >> >>Admittedly he was born in Victoria (in 1954) and wasn't moved to Queensland until 1963. > > Never heard of him. However, even your Wikipedia states: > > "In December 2012, on Christmas Day, Palmer hosted a buffet lunch for > 650 disadvantaged people, mostly children and their families." Among a > list of similar philanthropic activities, so he clearly doesn't > deserve your denigration. I suspect you only despise him for being a > conservative politician. As a Communist, you would naturally detest > anyone you percieve as 'counter-revolutionary' no matter how kind > hearted and charitable they may be.Just because he has a P.R. budget that doesn't make him a saint. -- Jasen.
Reply by ●June 6, 20212021-06-06
Right, so this is the block diagram that I have come up with so far: https://imgur.com/a/ZIbZz4y Not sure about the transmitter side - didn't find much in the way of clear explanations on the internet but the art of electronics says on the topic of FM transmission "it is often best to modulate at low deviation, then use frequency multiplication to increase the modulation index." (page 899, 2nd ed) so the block diagram does that. I don't know how I would go about multiplying all the way up to 915MHz, since a VCO based on op amps obviously won't go that high. I suppose I'll have to find and buy an off the shelf part for that step. I'm also no sure about the sidebands. I suppose I want a single sideband (SSB), but I have not quite figured out yet how to go about putting that in.
Reply by ●June 6, 20212021-06-06
harry.dud...@gmail.com wrote: ======================>> > > > Looking to build a sensible FM radio transmit/receive pair, designed for short range (10s of meters) and excellent audio quality. > > ** Just one system ? Mono or stereo ? AC or battery powered ? > > > Making for personal use, so very flexible on operating frequency, BOM cost etc. > > ** You are are aware of wireless mic systems for musical performances ? > > Most are variable frequency, wide band FM with "twin diversity" receivers on UHF. > > The latter is very important as single receivers work poorly indoors due to standing wave self cancellations. > > > > Building your own one sounds absurd > > > > Phil: > I just want to build one system.** ROTFL !> I know some FM use a difference signal for stereo but that sounds too complicated for my first project,** Really - you amaze me.> so I'll just build two systems and operate them of different bands for L/R.** Yeah -- that is real simple.> The system will be USB powered on the transmit side, and battery powered on the receive side > (I'll drill a hole in my headphones and tap off the battery).** Huh ? You have powered head phones ? > You are of course correct that it is absurd to build my own setup if the goal is to just get a working setup.> But this is a learning project** To learn what exactly ?> and so the journey is the important thing, not the destination!** So you regularly take random trips to nowhere ?>I will look into 'twin diversity' receivers for FM radio.** You need to do a *whole lot more* looking into than that.> Do you think I could avoid standing wave problems if I just occupied a huge bandwidth (say the whole 902-928MHz band)?** Depends where you a standing. You could try standing on you head for a start. Wot a raving lunatic...... ..... Phil
Reply by ●June 6, 20212021-06-06
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> Steve Wilson wrote: >> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >> [...] >> >>> You seen to be talking about a phase modulation (PM) system rather >>> than FM. That'll work, but it doesn't have FM's SNR advantage. >> >> I thought FM and PM were basically identical with the difference being >> the response to the modulation frequency. Audio equalization is used to >> compensate. > > They're both examples of _angle modulation_, but in practice are > completely different. The key distinguishing feature of FM over PM is > much wider deviation, leading to much better SNR for the same received > power. > > An angle modulator driven by a pure tone produces > > v = sin(2 pi f_0 t + M sin(2 pi f_mod t)). > > The modulation index M is the peak phase deviation in radians, and is > also the ratio of the RF and AF bandwidths. In the high-SNR limit, you > win SNR like 20 log M, so wideband is a big win. > > It's a lot more difficult to make a very wide-range, very linear phase > shifter than it is to make a good VCO.> Cheers> Phil HobbsVCO's are inherently nonlinear and drift due to temperature and time. This requires locking the vco to a crystal reference, which increases cost and complexity. It is difficult to correct for the nonlinearity. PM can use a crystal-controlled reference, eliminating drift. Bandwidth can be extended using frequency multiplication. Modern DSP techniques can produce any required type of modulation, for example the quadrature amplitude modulation (QAM)used in 802.11. This requires a crystal reference. SDR can modulate and demodulate any type of modulation, from AM, SSB, FM, PM, QAM, etc. This technology is rapidly overtaking the old conventional technologies and should be a focus for new studies in electronics and communications. -- The best designs occur in the theta state. - sw
Reply by ●June 6, 20212021-06-06
On Sunday, June 6, 2021 at 6:58:27 PM UTC-7, Steve Wilson wrote:> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > > > Steve Wilson wrote: > >> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > >> > >> [...] > >> > >>> You seen to be talking about a phase modulation (PM) system rather > >>> than FM. That'll work, but it doesn't have FM's SNR advantage. > >> > >> I thought FM and PM were basically identical with the difference being > >> the response to the modulation frequency. Audio equalization is used to > >> compensate. > > > > They're both examples of _angle modulation_, but in practice are > > completely different. The key distinguishing feature of FM over PM is > > much wider deviation, leading to much better SNR for the same received > > power. > > > > An angle modulator driven by a pure tone produces > > > > v = sin(2 pi f_0 t + M sin(2 pi f_mod t)). > > > > The modulation index M is the peak phase deviation in radians, and is > > also the ratio of the RF and AF bandwidths. In the high-SNR limit, you > > win SNR like 20 log M, so wideband is a big win. > > > > It's a lot more difficult to make a very wide-range, very linear phase > > shifter than it is to make a good VCO. > > > Cheers > > > Phil Hobbs > VCO's are inherently nonlinear and drift due to temperature and time. This > requires locking the vco to a crystal reference, which increases cost and > complexity. It is difficult to correct for the nonlinearity. > > PM can use a crystal-controlled reference, eliminating drift. Bandwidth can > be extended using frequency multiplication. > > Modern DSP techniques can produce any required type of modulation, for > example the quadrature amplitude modulation (QAM)used in 802.11. This > requires a crystal reference. > > SDR can modulate and demodulate any type of modulation, from AM, SSB, FM, > PM, QAM, etc. This technology is rapidly overtaking the old conventional > technologies and should be a focus for new studies in electronics and > communications. > -- > The best designs occur in the theta state. - swYep, but I am well familiar with digital techniques and the "haha let's just put it all in a computer" school of design and want to steer clear of it for this project. I'm not super worried about temperature drift since this is a personal project that won't be operated under a wide range of temperatures, but I did come across a crystal-stabilised design from Jim Williams here: https://www.analog.com/media/en/technical-documentation/application-notes/an14f.pdf that didn't seem *too* bad, so I'll do some back of the envelope calculations and see if it's likely to be a problem. Couldn't using the PLL on the receive side to lock into the incoming signal somehow also be used instead of temperature control, though? What is the difference between how the bandwidth is extended using frequency multiplication in a phase modulator as compared to how it needs to be extended in phase modulation? I thought they both used frequency multiplication (see diagram I posted).
Reply by ●June 7, 20212021-06-07
On Monday, June 7, 2021 at 11:58:27 AM UTC+10, Steve Wilson wrote:> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > > > Steve Wilson wrote: > >> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > >> > >> [...] > >> > >>> You seen to be talking about a phase modulation (PM) system rather > >>> than FM. That'll work, but it doesn't have FM's SNR advantage. > >> > >> I thought FM and PM were basically identical with the difference being > >> the response to the modulation frequency. Audio equalization is used to > >> compensate. > > > > They're both examples of _angle modulation_, but in practice are > > completely different. The key distinguishing feature of FM over PM is > > much wider deviation, leading to much better SNR for the same received > > power. > > > > An angle modulator driven by a pure tone produces > > > > v = sin(2 pi f_0 t + M sin(2 pi f_mod t)). > > > > The modulation index M is the peak phase deviation in radians, and is > > also the ratio of the RF and AF bandwidths. In the high-SNR limit, you > > win SNR like 20 log M, so wideband is a big win. > > > > It's a lot more difficult to make a very wide-range, very linear phase > > shifter than it is to make a good VCO. > > VCO's are inherently nonlinear and drift due to temperature and time.Not necessarily. Real components do age and have some temperature dependence.> This requires locking the vco to a crystal reference, which increases cost and > complexity. It is difficult to correct for the non-linearity.Locking an oscillator to a crystal reference can reduce some forms of drift. If you don't know what non-linearity you have to correct for, it's obviously going to be difficult to engineer a correction.> PM can use a crystal-controlled reference, eliminating drift.Crystal-controlled references still drift. https://en.wikipedia.org/wiki/Caesium_standard> Bandwidth can be extended using frequency multiplication.Only in the sense that if you multiply up a frequency range, it covers a wider bandwidth.> Modern DSP techniques can produce any required type of modulation, for > example the quadrature amplitude modulation (QAM)used in 802.11. This > requires a crystal reference.Quadrature amplitude modulation refers to the way the signal is constructed, not it's frequency stability. You probably wouldn't bother with such a complicated scheme if you didn't have a stable frequency source, but it isn't any kind of requirement.> SDR can modulate and demodulate any type of modulation, from AM, SSB, FM, PM, QAM, etc.Software defined radio may be able to do all of this, and lots more besides, but it needs an analog front end to convert the incoming signal into something that can be digitised and processed, or turn the digital bit stream being generated into a bandwidth limited signal without lots of higher harmonics. A D/A converter does produce a stair-case waveform, unless you get very subtle.> This technology is rapidly overtaking the old conventional technologies and should be a focus for new studies in electronics and communications.In some areas. Software does run on hardware, though programmers don't like to admit it. -- Bill Sloman, Sydney
Reply by ●June 7, 20212021-06-07
"Harry Dudley-Bestow" <harry.dudleybestow@gmail.com> wrote in message news:669bc2aa-92e8-4290-a91b-6b3f34bff7bbn@googlegroups.com...>Looking to build a sensible FM radio transmit/receive pair, designed for >short range (10s of meters) and excellent audio quality. Making for >personal use, so very flexible on operating frequency, BOM cost etc.>Had a look in my go-to Art of Electronics (not enough detail) and tried to >find an app note or something on the subject, no dice. Designs on the >internet have no explanations alongside them and are far too optimised for >low BOM count at expense quality of output.>Anyone got recommendations for design resources on the subject?"Looking to build a sensible FM radio transmit/receive pair, designed for short range (10s of meters) and excellent audio quality. Making for personal use," "The project needs to be RF because I've arbitrarily decided to do an RF project :)" "the idea of this project was a fun and educational thing, not necessarily a practical one." "would like to have a high quality audio signal." "and is it possible to get audio that is more or less indistinguishable to the kind you get over a copper cable?" "I don't know what the efficiency of a FM radio transmitter is" "Discrete PLL's can apparently be a bit tricky to do in discrete components" "but I am well familiar with digital techniques" "I just want to build one system" "I'll drill a hole in my headphones and tap off the battery" "Do you think I could avoid standing wave problems if I just occupied a huge bandwidth" "I'm also no sure about the sidebands. I suppose I want a single sideband (SSB), but I have not quite figured out yet how to go about putting that in." "I failed to specify that my project must be designed using only classic RF components like our forefathers used, no all-in-one IC's allowed." Now that we have a full requirement specification I think one of these would be most suitable for use in the receiver: http://www.r-type.org/exhib/aaa1272.htm I've always wanted to use one but never have. It looks way more fun that a dual gate mosfet. There are some practical circuits here: https://www.radiomuseum.org/forum/fm_demodulation_weniger_bekannte_verfahren_1.html It shouldn't be hard to make a low power transmitter. for example: https://www.electroschematics.com/low-power-fm-transmitter/ But if I wanted high quality audio over a distance of 10s of meters I'd consider longitudinal pressure waves sent through the air, assuming it didn't disturb anyone else. Suitable transmitters are readily available and you've already got a receiver or two.
Reply by ●June 7, 20212021-06-07
Steve Wilson wrote:> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Steve Wilson wrote: >>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>> [...] >>> >>>> You seen to be talking about a phase modulation (PM) system rather >>>> than FM. That'll work, but it doesn't have FM's SNR advantage. >>> >>> I thought FM and PM were basically identical with the difference being >>> the response to the modulation frequency. Audio equalization is used to >>> compensate. >> >> They're both examples of _angle modulation_, but in practice are >> completely different. The key distinguishing feature of FM over PM is >> much wider deviation, leading to much better SNR for the same received >> power. >> >> An angle modulator driven by a pure tone produces >> >> v = sin(2 pi f_0 t + M sin(2 pi f_mod t)). >> >> The modulation index M is the peak phase deviation in radians, and is >> also the ratio of the RF and AF bandwidths. In the high-SNR limit, you >> win SNR like 20 log M, so wideband is a big win. >> >> It's a lot more difficult to make a very wide-range, very linear phase >> shifter than it is to make a good VCO.> > VCO's are inherently nonlinear and drift due to temperature and time. This > requires locking the vco to a crystal reference, which increases cost and > complexity. It is difficult to correct for the nonlinearity.Nonsense. You can phase lock to even rapidly drifting signals. Old timey entertainment radios use AFC, i.e. they dork the LO slightly to keep the signal centred in the IF passband. That's an example of a frequency-locked loop (FLL). And making linear VCOs isn't as hard as all that. You can use an integrator/Schmitt trigger oscillator, which can get down to ~0.1% nonlinearity (the ancient LM331 does this, but it can be done much faster). Alternatively you can use an LC linearized using an off-stage resonance. (series and parallel inductors plus a dual varactor).> > PM can use a crystal-controlled reference, eliminating drift. Bandwidth can > be extended using frequency multiplication.Deviation can be extended, not modulation bandwidth. But you're complaining about ordinary VCOs being nonlinear, and still suggesting a _VCXO_? Frying pan, fire, etc.> > Modern DSP techniques can produce any required type of modulation, for > example the quadrature amplitude modulation (QAM)used in 802.11. This > requires a crystal reference.All true, but pretty droll when the OP thinks that there might be such a thing as single-sideband FM.> SDR can modulate and demodulate any type of modulation, from AM, SSB, FM, > PM, QAM, etc. This technology is rapidly overtaking the old conventional > technologies and should be a focus for new studies in electronics and > communications.Depends for what. The OP is probably not going to be using direct digitization at 900 MHz for a battery-powerd hobby project, and I'm not going to be using $20k worth of lithium niobate modulators to put FM sidebands on my diode laser, even if they worked at my wavelength. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●June 7, 20212021-06-07
Harry Dudley-Bestow wrote:> Right, so this is the block diagram that I have come up with so far: > https://imgur.com/a/ZIbZz4y > > Not sure about the transmitter side - didn't find much in the way of > clear explanations on the internet but the art of electronics says > on the topic of FM transmission "it is often best to modulate at low > deviation, then use frequency multiplication to increase the > modulation index." (page 899, 2nd ed) so the block diagram does > that. I don't know how I would go about multiplying all the way up to > 915MHz, since a VCO based on op amps obviously won't go that high. I > suppose I'll have to find and buy an off the shelf part for that > step. I'm also no sure about the sidebands. I suppose I want a single > sideband (SSB), but I have not quite figured out yet how to go about > putting that in. >Ain't no such animal as SSB FM. For an educational project, it's worth going through the derivation of the FM spectrum. You'll need Wolfram Alpha or a copy of Abramowitz & Stegun to get the Bessel function expansion, but it's about a third-year undergraduate problem. When you do it, you find that the FM spectrum is made up op of a forest of sidebands. The nth-order sideband amplitude is proportional to J_n(m), where m is the modulation index (see one of my earlier posts). The math is not difficult, and it's really quite pretty. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
