Looking for FM receiver

[sobazz]

Why is it so hard to find a FM receiver projekt on the internet? I've have only found one, and it didn't look very interesting. Do any of you guys know a construction worth building?

[CheffDeGaar]

Feel the same. Hard to find....
Which project did you find ?

I found this one , which looks quit interesting. I want to give it a try, and began to draw a PCB, but some details still puzzle me... Tried to e-mail the author, but he's unreachable. Have someone here built this project, or part of ?

[jackinnj]

there is a FM Tuner newsgroup on yahoo at:
http://groups.yahoo.com Yahoo is a pain to work with, too cumbersome, too many ads.

there seems to be a lack of willingness to get fingers dirty for most audio DIY'rs with a project like this, but it certainly isn't out of the realm of ham radio types who build 144MHz receivers and tuners all the time. I think that one of the best approaches would be to cannibalize an FM3 with a new front end.

most "off the shelf" multiplexer chips are out of production.

jack

[miguel2]

That article seems to be a bit complex. Aren't there any chips that one can use to make a good FM receiver without so many parts?

I once have looked for schematics too and found just a bunch of 'toy' radios...

Miguel

[AuroraB]

RF circuit design contitutes skills and knowledge quite different from even high end audio design. Furthermore the PCB layout often requires experience not found in books, often to be learned the hard way...even if your circuit is perfect, a bad PCB design can yield a totally nogo result, struggling with stray capacitance, signal crosstalk etc.

A top notch receiver requires a RF gain of 100-110 dB before the demodulator. Getting a stable design is difficult at best, - but of course, there are ways.....

Then the design adresses contradicting requests,- a very good mixer must produce well controlled 2nd harmonics, and nothing more in terms of higher order harmonics, the RF amplifiers should produce no harmonics, - of course....
The local oscillator should be frequency stable, and as pure as possible,- no phase noise etc.etc ( something for the CD clock bunch..) and so on and so forth.......

I have been reading both RF and audio mags for more than 30 years, and FM receivers have been rare, - good ones even rarer...
I have found only a couple of very good ones in total,- on in Ham Radio mag " UKW Berichte" in the early 70s, and two in Elektor in the late 80s and early 90s, all of them using parts I strongly suspect is no longer available, - including the frequency synth chips used in the latter two.

Working professionally if RF and instrumentation, and with audio as a long time hobby, the design referred by Cheff is a rather average one,- if a circuit board can be made. Except for the kicks of building radio circuits, which I fully understand, any 100-200 $ tuner in the shop will give rather similar quality, soundwise....and quite frankly, - listening to the radio stations in my corner of the world does not require anything better qualitywise..

[CheffDeGaar]

Miguel2,
Philips' SA602 and SA604, along with Application Note AN1993 could make a good starting point. But browse their website, you may find something interesting...

AuroraB,
Glad to have at last an expert advice about Ryder's design. For a dummy head like me, what makes you qualify it as "average" ?
I've too noticed Elektor's designs, but I'm absolutely not qualified to say they're good or not... Will try to dig in my old issues of the magazine, just to check we're talking about the same designs...

By any chance, do you have a copy of the Ham Mag article ? Should be nice...

[AuroraB]

Cheff......

I took time to read through the referred article once again, this time more thoroughly...

This time, I also recognized Wayne Ryder's name from my earlier subsriptions to various ham radio magazines, with several excellent articles............and a closer look probably says that this design is not bad at all, - albeit incomplete as a project, as it lacks the both stereo decoder and the control CPU to drive the frequency synthesizer. What mr.Ryder does here, is to address some of the problems I described, with conflicting demands on a.o. the RF front end. He also points to the importance of linear phase and group delay in the MF filters, here by using a Murata filter I don't know. Most average receivers will indeed use Murata ( or Toko ) filters of lower quality, price appx. 1$ or less piece. If you look to the Elektor designs, they use two rather expensive crystal filters from Toyocom ( as did the UKW article ). 15 years ago, I could still get hold of these for appx. 40-50$ apiece, --nowadays I don't have clue...have tried sarching but no luck....
He also addresses the problems of detector linearity andS/N by seemingly very careful component selection...

For the "UKW Berichte" article, I should have a bad copy somewhere, but it is very close to the later of the Elektor designs, except for the synthesizer, which of course is "Flintstone tech", by comparison......

To sum up,- by closer inspection, this article could be the basis of a very good kit, if complete. With the current state of affairs, it is a true "research project"

BTW- the Elektor designs should still be managable, if you can find the parts, filters and synth chips in particular. And- I guess you would have to write your own program, - I don't think Elektor still delivers the EPROMS ??? If I can be of any help,-ask away.....

[jackinnj]

Originally posted by CheffDeGaar
Miguel2,
Philips' SA602 and SA604, along with Application Note AN1993 could make a good starting point. But browse their website, you may find something interesting...

AuroraB,
Glad to have at last an expert advice about Ryder's design. For a dummy head like me, what makes you qualify it as "average" ?
I've too noticed Elektor's designs, but I'm absolutely not qualified to say they're good or not... Will try to dig in my old issues of the magazine, just to check we're talking about the same designs...

By any chance, do you have a copy of the Ham Mag article ? Should be nice...

Everything is "critical" -- but there are circuit diagrams and PCB layouts for much lower noise 2 meter (and up) front ends all over the place., there are now DDS chips with eval boards readily available.

while we are at it, someone should also make a half-decent a.m. receiver again.

[CheffDeGaar]

Hello, Norway !
Nice place (been there 2 years ago), but expensive one

Originally posted by AuroraB
Cheff......

I took time to read through the referred article once again, this time more thoroughly...

This time, I also recognized Wayne Ryder's name from my earlier subsriptions to various ham radio magazines, with several excellent articles............and a closer look probably says that this design is not bad at all,

AuroraB...
(with the nice solar eruptions I was told we have these days, you should be glowing strong ) - Sorry, couln't resist- hope you don't mind

Thanks for taking the time to reread Mr Ryder's article ! A small search in the news groups shown me other people share your opinion. So it is worth a try...

- albeit incomplete as a project, as it lacks the both stereo decoder and the control CPU to drive the frequency synthesizer.

Well, that's a point, but not the major issue IMHO. If only I could have something working with basic implementations of such features, I should be happy... But this sure should be addressed, and solutions are somewhat numerous for this.

What mr.Ryder does here, is to address some of the problems I described, with conflicting demands on a.o. the RF front end. He also points to the importance of linear phase and group delay in the MF filters, here by using a Murata filter I don't know.

Specs are here. Do these specs sound good to you ? Prices are not too high, approx between 1 and 2 Euros...

Most average receivers will indeed use Murata ( or Toko ) filters of lower quality, price appx. 1$ or less piece. If you look to the Elektor designs, they use two rather expensive crystal filters from Toyocom ( as did the UKW article ). 15 years ago, I could still get hold of these for appx. 40-50$ apiece, --nowadays I don't have clue...have tried sarching but no luck....

Wow, not exactly cheap !!! I didn't have the time to check my Elektor issues, normally this WE...

He also addresses the problems of detector linearity andS/N by seemingly very careful component selection...

To sum up,- by closer inspection, this article could be the basis of a very good kit, if complete. With the current state of affairs, it is a true "research project"

I totally agree regarding component selection... I've already sourced the major part of he components, but I have some difficulties with the coils... The Toko coils (L6,L7,L9,L10,L12) can be sourced via Digikey for US or BEC (UK), but I could find neither the IF quad coil from Sumida (235S01 SNY-074-1919A) - no reference of it at Sumida's website -, nor the Toko equivalent given by Sanyo in the LA1235 datasheet (Part nr : Q228CEL-1077B). All I found is a toko quad coil (Q228CEL1064L on BEC's site. But I don't know if it can be used without problems.... Do you have any hint on sourcing the original Sumida coil, or if the last Toko quad coil would fit in the design ?

The other (and last ) main thing that puzzles me in this design concerns the input coil (L6 on the schematic) : as far as I know, the MC 120 coils don't have intermediate winding. And here, the RF input seems to enter the circuit through such an arrangement... Do I have to make it myself, calculating the impedance required to have 75 Ohms, and adding an entry point to the coil to get this input impedance, or is there any "logical" explanation ?

For the "UKW Berichte" article, I should have a bad copy somewhere, but it is very close to the later of the Elektor designs, except for the synthesizer, which of course is "Flintstone tech", by comparison......

BTW- the Elektor designs should still be managable, if you can find the parts, filters and synth chips in particular. And- I guess you would have to write your own program, - I don't think Elektor still delivers the EPROMS ???

Thanks a lot . If the German article is close to Elektor's, I will try to stick to the latter. The filters availability frightens me, but who knows... Will serach my papers this WE...

If I can be of any help,-ask away.....

Just look above . Thanks for being so helpful. And I'm sure we can manage to get something working, and of nice quality, despite the awful quality of the majority of FM broadcasts....

Cheers,