On Monday, June 14, 2021 at 2:57:23 AM UTC+10, Cursitor Doom wrote:> On Sun, 13 Jun 2021 06:37:43 -0700 (PDT), Bill Sloman > <bill....@ieee.org> wrote: > > >On Sunday, June 13, 2021 at 8:37:03 PM UTC+10, Cursitor Doom wrote: > >> On Tue, 8 Jun 2021 20:18:24 -0700 (PDT), Bill Sloman > >> <bill....@ieee.org> wrote: > >> >On Wednesday, June 9, 2021 at 9:30:07 AM UTC+10, Brian Gregory wrote: > >> >> On 05/06/2021 19:36, Harry Dudley-Bestow wrote: > >> >> > On Saturday, June 5, 2021 at 11:31:34 AM UTC-7, Ed Lee wrote: > >> >> >> On Saturday, June 5, 2021 at 11:14:09 AM UTC-7, 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. 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? > >> >> >> This should work: > >> >> >> > >> >> >> https://www.mouser.com/datasheet/2/268/microchip_technology_mchp-s-a0001247358-1-1738104.pdf > >> >> >> > >> >> >> But I haven't look too deeply into it. > >> > >> >> > Sorry Ed 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. > >> >> > >> >> Daft question about an almost impossible to do and almost impossible to > >> >> do legally project with more and more ludicrous restrictions being added > >> >> rapidly with each message posted. > >> >> > >> >> This is clearly a very nasty troll of just about the worst kind. > >> Eh??? > >> > > >> >Not really. More a classical dumb newbie, of the more than usually incompetent sort. Trolls are malicious. > >> > >> You of all people would know. > > > >You, Flyguy and John Larkin remind me of it more or less nonstop. Happily all of you are remarkably pathetic in your malice. Jim Thompson once claimed to have denounced me to the FBI which struck me as excessive. > > Oh really? THAT struck you as excessive, but your wish to see John and I hanged for disagreeing with you is perfectly reasonable??I don't recall that I've ever expressed a desire to see either of you hanged. Disagreeing with me doesn't strike me as a qualifying as a capital crime.> >> Couldn't resist a gratuitous put-down as usual. > > > >That put-down was well-earned, rather than gratuitous. > > No it wasn't. The OP's question - from a technical standpoint at any rate - was 100% on topic for this group.And your ideas about technical matters are worth expressing? In fact the problem was that he changed the specification as he went along.> >> Never miss up on an opportunity to throw in a supercillious slur, eh, Bill? > > > >It's hard to avoid being supercilious when confronted by people who offer a lot to be supercilious about. You'd be a prime example of somebody who must get that reaction frequently. > > As ever, you demonstrate a grandiose sense of self-worth. I believe I've already informed you of what that trait is symptomatic of.If I ever had a grandiose sense of self-worth, it would have been drained away by working with people who were just as smart as I am - and I worked at EMI Central Research for a couple of years, where they were thick on the ground. Grow up. -- Bill Sloman, Sydney
FM radio design resources
Started by ●June 5, 2021
Reply by ●June 13, 20212021-06-13
Reply by ●January 2, 20222022-01-02
Time has passed, and the circuit has been built: https://imgur.com/a/g9y31uO As it stands thought the output is 7.5MHz, 500mVpp centered at around 2V. It has sidelobes 18 dB down though :(, I was assured by the art of electronics that 60dB was the default!. I tried increasing C13 to reduce the feedback using the variable capacitor in the picture, but it did not seem to change much, only shifting the frequency slightly. What ideas do people have surrounding how to reduce the sidelobes?
Reply by ●January 3, 20222022-01-03
Harry Dudley-Bestow wrote:> Time has passed, and the circuit has been built: > https://imgur.com/a/g9y31uO As it stands thought the output is > 7.5MHz, 500mVpp centered at around 2V. It has sidelobes 18 dB down > though :(, I was assured by the art of electronics that 60dB was the > default!. I tried increasing C13 to reduce the feedback using the > variable capacitor in the picture, but it did not seem to change > much, only shifting the frequency slightly. What ideas do people have > surrounding how to reduce the sidelobes? >By 'sidelobes', do you mean harmonics, FM sidebands, or ....? Thanks 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 ●January 3, 20222022-01-03
On Monday, January 3, 2022 at 4:49:01 PM UTC-8, Phil Hobbs wrote:> Harry Dudley-Bestow wrote: > > Time has passed, and the circuit has been built: > > https://imgur.com/a/g9y31uO As it stands thought the output is > > 7.5MHz, 500mVpp centered at around 2V. It has sidelobes 18 dB down > > though :(, I was assured by the art of electronics that 60dB was the > > default!. I tried increasing C13 to reduce the feedback using the > > variable capacitor in the picture, but it did not seem to change > > much, only shifting the frequency slightly. What ideas do people have > > surrounding how to reduce the sidelobes? > > > By 'sidelobes', do you mean harmonics, FM sidebands, or ....? > > Thanks > 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.comMy bad. I mean that the output of the circuit with no modulation or any other input applied is not a particularly perfect sine wave. These pictures should clarify what I mean. It's the output of the circuit (which has a DIY 10:1 attenuator on it) https://photos.app.goo.gl/ayw8ERykW7cTUKv88 I assume this means that the sound will come out all wrong.
Reply by ●January 3, 20222022-01-03
Harry Dudley-Bestow wrote:> On Monday, January 3, 2022 at 4:49:01 PM UTC-8, Phil Hobbs wrote: >> Harry Dudley-Bestow wrote: >>> Time has passed, and the circuit has been built: >>> https://imgur.com/a/g9y31uO As it stands thought the output is >>> 7.5MHz, 500mVpp centered at around 2V. It has sidelobes 18 dB >>> down though :(, I was assured by the art of electronics that 60dB >>> was the default!. I tried increasing C13 to reduce the feedback >>> using the variable capacitor in the picture, but it did not seem >>> to change much, only shifting the frequency slightly. What ideas >>> do people have surrounding how to reduce the sidelobes? >>> >> By 'sidelobes', do you mean harmonics, FM sidebands, or ....?>> http://electrooptical.net http://hobbs-eo.com > My bad. I mean that the output of the circuit with no modulation or > any other input applied is not a particularly perfect sine wave. > These pictures should clarify what I mean. It's the output of the > circuit (which has a DIY 10:1 attenuator on it) > https://photos.app.goo.gl/ayw8ERykW7cTUKv88 > > I assume this means that the sound will come out all wrong.Not necessarily. You can put an FM signal through a frequency multiplier, for instance, and get perfectly good sound nonetheless. Thing is, the waveform is an amplitude thing, whereas the modulation is a phase thing. 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 ●January 3, 20222022-01-03
> Not necessarily. You can put an FM signal through a frequency > multiplier, for instance, and get perfectly good sound nonetheless. > > Thing is, the waveform is an amplitude thing, whereas the modulation is > a phase thing. > > 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.comInteresting! In that case, I shall proceed onwards with constructing the receiver, and deal with new problems as they arise.
Reply by ●July 22, 20222022-07-22
Well time has gone by and I have got the PLL working! Input to a VCO is green, output from the PLL control signal is blue: https://photos.app.goo.gl/WtgUkvxBuhWBNv9k6 It locks from between about 10-11MHz and can be used to demodulate FM audio just fine. For the final "productionised" version I would like to remove the negative rail I am using for my loop filter amplifier. Currently the loop filter is a simple two transistor diff amp: https://photos.app.goo.gl/7hiqrjRzVVpj3TqC6 However in order for the input to go to 0V, this requires a negative voltages source which for a battery powered device is not ideal. My question is: What is the simplest possible amplifier where the input can go to the negative rail? From some reading in the "Design of Analog CMOS Integrated Circuits" I understand that something may be possible with a pmos diff pair, but I cannot get anything to work in simulation. @Phil Hobbs any ideas?
Reply by ●July 23, 20222022-07-23
Harry Dudley-Bestow wrote:> Well time has gone by and I have got the PLL working! Input to a VCO > is green, output from the PLL control signal is blue: > https://photos.app.goo.gl/WtgUkvxBuhWBNv9k6Nice.> > It locks from between about 10-11MHz and can be used to demodulate FM > audio just fine. For the final "productionised" version I would like > to remove the negative rail I am using for my loop filter amplifier. > Currently the loop filter is a simple two transistor diff amp: > https://photos.app.goo.gl/7hiqrjRzVVpj3TqC6 However in order for the > input to go to 0V, this requires a negative voltages source which for > a battery powered device is not ideal. > > My question is: What is the simplest possible amplifier where the > input can go to the negative rail? > > From some reading in the "Design of Analog CMOS Integrated Circuits" > I understand that something may be possible with a pmos diff pair, > but I cannot get anything to work in simulation. @Phil Hobbs any > ideas? >Well, there are lots of RRIO CMOS op amps out there, e.g. . If you want something discrete, a PNP diff pair with a resisitive pulldown would work, and be a lot quieter than discrete small-signal PFETs, which are pretty scarce nowadays anyway. Something like that obviously won't pull down very strongly near ground, but then all you're driving is a varactor, right? 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 ●July 23, 20222022-07-23
Harry - there are numerous op amps that allow the input below the negative rail. I can't recall a specific number though. The rail to rail devices Phil mentions might be a good starting point for a search. These have, I believe, both p & n channel devices on the input. The ones I vaguely rember were input from below negative to within 2 volts of positive. Hul Harry Dudley-Bestow <harry.dudleybestow@gmail.com> wrote:> Well time has gone by and I have got the PLL working! > Input to a VCO is green, output from the PLL control signal is blue: > https://photos.app.goo.gl/WtgUkvxBuhWBNv9k6> It locks from between about 10-11MHz and can be used to demodulate FM audio just fine. > For the final "productionised" version I would like to remove the negative rail I am using for my loop filter amplifier. > Currently the loop filter is a simple two transistor diff amp: > https://photos.app.goo.gl/7hiqrjRzVVpj3TqC6 > However in order for the input to go to 0V, this requires a negative voltages source which for a battery powered device is not ideal.> My question is: What is the simplest possible amplifier where the input can go to the negative rail?> From some reading in the "Design of Analog CMOS Integrated Circuits" I understand that something may be possible with a pmos diff pair, but I cannot get anything to work in simulation. @Phil Hobbs any ideas?
Reply by ●July 23, 20222022-07-23
Thanks for the input. Hul I am aware of rail to rail input amps :). What I would like to do for my project is make something using discrete components. I will try out the PNP diff pair and see how it goes. I am not so sure where this "resistive pulldown is supposed to go but all will become clear, I'm sure.
