FM radio design resources

On Monday, June 7, 2021 at 8:51:51 AM UTC+10, Cursitor Doom wrote:
> On Sun, 6 Jun 2021 08:14:43 -0700 (PDT), Bill Sloman
> <bill....@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.

That's just getting attention by "any means".

> I suspect you only despise him for being a  conservative politician.

Actually he is a crooked business-man,  who got into politics because he didn't have enough money bribe his way out of the hole his incompetence had dug him into.

>  As a Communist, you would naturally detest  anyone you perceive as 'counter-revolutionary' no matter how kind -hearted and charitable they may be.

Clive Palmer is neither kind-hearted nor charitable. He's not all that convincing when he tries to act as if he is - maybe convincing enough to fool you, which is a pretty low bar.

And I'm not the last surviving Communist in the western world - that species became extinct here quite a while ago. Any time now you will be calling me a Tasmanian Tiger (or thylacine) which is no less extinct. You really don't have any grasp of reality, do you.

-- 
Bill Sloman, Sydney

On Monday, June 7, 2021 at 6:40:33 AM UTC-7, Phil Hobbs wrote:
> 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
Ah, I think I was messing up my modulations. Was looking at Art of Electronics 2nd ed page 898:
https://imgur.com/a/pLAUnOQ
I suppose at this point going through the maths would be a good idea. Sound more fun than trying to find models to get all this into LTSpice, anyway...
I guess that means I can proceed with putting in components for the block diagram I put down before:
https://imgur.com/a/ZIbZz4y
although it looks like I will need an integrated IC since apparently using a mixer to upconvert FM to 915MHz may not be a thing.Perhaps the maths will elucidate...

In article <a5a46160-48f1-4207-82bc-7f09f548cdb1n@googlegroups.com>,
Harry Dudley-Bestow  <harry.dudleybestow@gmail.com> wrote:
>From looking around it looks like my main choices are quadrature detector and PLL demodulation on the receive side. For my taste the quadrature
>detection is better since it is made out of discrete inductor + capacitor to get the phase delay rather than a newfangled IC, but I can't seem to find
>out if it's possible to get good quality audio out of it.

>Naively it seems to me that a large signal bandwidth compared to the IF would be the limiting factor, since that would push the phase shift out of the
>linear sin(x) = x region. Is my intuition correct here, and is it possible to get audio that is more or less indistinguishable to the kind you get
>over a copper cable?

IC-based quadrature detector ICs for FM stereo have to deal with a
signal bandwidth of 60 kHz or more (and an IF bandwidth of more than
that, per Carson's Rule).  Quite a few well-spoken-of commercial FM
tuners and receivers use these ICs.  So, if all you need is mono audio
with a 20 kHz frequency range, I don't think you'd be pushing the
envelope.

The quadrature coils ("transformers" although they aren't, really)
usually have a swamping/damping resistor in parallel with each LC
tuned circuit, to reduce the Q and thus increase the width of the
linear range.  For example, the LA1235 data sheet calls out a couple
of different models of quad-coil can (one Toko, one Sumiko) and the
damping-resistor values are different (I presume to compensate for
different impedances of the LC circuit components).  [Both of these
particular coils are essentially unobtanium now - I can't even find
data sheets for them - so you may have to wind your own quad-coil (or
add a cap to a standard single-coil can) and do some
experimentation to tweak the design.]

For what it's worth: some years ago I helped debug an audio-quality
problem in a commercially-build amateur-radio repeater (2-meter band)
which uses a quadrature detector.  The audio was distorting, and then
clipping, on normal voice-speaking IF deviations... the distortion was
bad enough that DTMF tones couldn't control the repeater properly.  We
tracked the problem down to the quad coil - the manufacturer had
changed coil types when the original model went out of production, and
hadn't realized that the new coil's higher Q required more damping
(smaller R in parallel).  A simple change to this resistor changed the
audio from harsh, to clean and pristine.  We notified the manufacturer
and they changed their next production run, with very happy results.

You might want to skim through some of the FM stereo tuner
descriptions at fmtunerinfo.com, look for models that mention
quadrature detection and discrete components, and look at the
schematics for inspiration.  Green and Bourque's "The Theory and
Servicing of AM, FM, and FM Stereo Receivers" might also be useful,
although they give scant coverage to quadrature IF detectors.

A friend of mine (now in his early 80s) did a college project which
involved building an FM receiver... this was back in the tube era.  If
I recall correctly he designed and built a tube-based pulse-count FM
detector, and wowed his instructor with clean reception from an FM
station about 40 miles away (he described it as "sounding as if it was
wired").  He's been threatening to dig through his attic to see if he
still has the board; I'd love to see it, if so.

My impression is that getting really-low-distortion FM is a harder
problem on the transmitter side than the receiver side.  Most
modulators use varactors, and their response isn't surpremely linear.
You might want to take a look at the schematic for the venerable Sound
Technology 1000A FM alignment generator - they managed to do an
impressive job with a varactor-and-single-transistor RF oscillator.

Dave Platt wrote:
> In article <a5a46160-48f1-4207-82bc-7f09f548cdb1n@googlegroups.com>, 
> Harry Dudley-Bestow  <harry.dudleybestow@gmail.com> wrote:
>> From looking around it looks like my main choices are quadrature
>> detector and PLL demodulation on the receive side. For my taste the
>> quadrature detection is better since it is made out of discrete
>> inductor + capacitor to get the phase delay rather than a
>> newfangled IC, but I can't seem to find out if it's possible to get
>> good quality audio out of it.
> 
>> Naively it seems to me that a large signal bandwidth compared to
>> the IF would be the limiting factor, since that would push the
>> phase shift out of the linear sin(x) = x region. Is my intuition
>> correct here, and is it possible to get audio that is more or less
>> indistinguishable to the kind you get over a copper cable?

<sniiip>
> 
> My impression is that getting really-low-distortion FM is a harder 
> problem on the transmitter side than the receiver side.  Most 
> modulators use varactors, and their response isn't surpremely
> linear. You might want to take a look at the schematic for the
> venerable Sound Technology 1000A FM alignment generator - they
> managed to do an impressive job with a varactor-and-single-transistor
> RF oscillator.
> 

A wide-range VCO built with a hyperabrupt varactor has pretty nearly 
linear tuning, and as I noted upthread it can be linearized further by 
using series and parallel inductors.

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

On Sun, 6 Jun 2021 17:07:28 -0700 (PDT), Harry Dudley-Bestow
<harry.dudleybestow@gmail.com> 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.

What I used to do IIRC (and I'm going back a hell of a way here) is to
take a crystal oscillator's output and pass it through a Schmidt
Trigger (or whatever you can find that switches very fast). That gives
an output that's rich in harmonics. You then make a filter for the
highest stable harmonic to pass on to your power amplification
stage(s).

On Mon, 7 Jun 2021 07:30:50 -0700 (PDT), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Monday, June 7, 2021 at 8:51:51 AM UTC+10, Cursitor Doom wrote:
>> On Sun, 6 Jun 2021 08:14:43 -0700 (PDT), Bill Sloman
>> <bill....@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.
>
>That's just getting attention by "any means".
>
>> I suspect you only despise him for being a  conservative politician.
>
>Actually he is a crooked business-man,  who got into politics because he didn't have enough money bribe his way out of the hole his incompetence had dug him into.
>
>>  As a Communist, you would naturally detest  anyone you perceive as 'counter-revolutionary' no matter how kind -hearted and charitable they may be.
>
>Clive Palmer is neither kind-hearted nor charitable. He's not all that convincing when he tries to act as if he is - maybe convincing enough to fool you, which is a pretty low bar.

So your wonderful Wikipedia is wrong, then? Whoever wrote the article
about him was fooled and Wikipedia published a falsehood! Just imagine
that...
Yet no doubt you'll still be citing from it in future like it's a
trustworthy source LOL!

On Mon, 07 Jun 2021 01:04:45 +0300, LM <sala.nimi@mail.com> wrote:

>On Sat, 5 Jun 2021 11:14:05 -0700 (PDT), Harry Dudley-Bestow
><harry.dudleybestow@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?
>You should search one transistor FM (transmitter)

It's ingenious how they do all that with just one transistor in some
designs. I think they use a BJT with a suitable BC junction
capacitance and apply the audio control voltage to it. Saves using a
varactor diode!

On Mon, 7 Jun 2021 09:29:30 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>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.

On that subject (forgive me if it's already been suggested) the
Chinese sell cheap but powerful lasers and just a 50 cent 5mW one
ought to be able to convey a modulated signal over 20 meters or so
that the OP requires, surely?

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.

killfile it.

-- 
Brian Gregory (in England).

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. 

Not really. More a classical dumb newbie, of the more than usually incompetent sort. Trolls are malicious.

> killfile it. 

Just ignore it.

-- 
Bill Sloman, Sydney