FM radio design resources

Why not use an infra-red diode pair to transmit / receive? No legal problems.

This should work:

But I haven't look too deeply into it.

Yep I have considered that, was thinking of using a huge IR LED bounced off the ceiling, and receiver on my headphones. There are a bunch of bands that are OK for radios though, should be able to just use one of those I would think. The project needs to be RF because I've arbitrarily decided to do an RF project :) I did consider blasting a massive IR LED at the ceiling, but I already have some experience with optical stuff and besides, I am not sure how I would go about getting low noise for the audio signal. Background noise would be a problem and I don't know that a high power LED would have enough bandwidth to upconvert to a reasonable frequency or not.

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.

Youtube

There have been COTS "infrared headphones". The downside is, of course, line of sight (step "around the corner" and the dropoff is monumental!)

Finally a purist! Welcome aboard!

Thanks for the recommendation amdx, I'll check it out.

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?

good DIY FM transmitters and receivers was difficult in the old days and it still is. You can Google pirate FM, Pirate radio and so on, because that's what they are.

snipped-for-privacy@gmail.com wrote: ==========================

** Just one system ? Mono or stereo ? AC or battery powered ? ** 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

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 you'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 = Shit for Brains Usenet Criminal.

==========================================

** ROTFL !!!

Been dealing with it, hobby and professional, very much hands on, all my life.

The OP is a trolling, know nothing f****it.

You are such an hee hawing ass you can't possibly tell the difference.

..... Phil

In the old days before quadrature and PLL detectors some descrete "pulse count" discriminators were used at low-ish intermediate frequencies for high quality audio reproduction with fewer parts. Should be some 1960s designs online.

I think you will find building the hifi micro-power transmitter will be much easier than building the matching receiver.

piglet

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.

Warum sagst du das, klein Piglet?

I rest my case.

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.

Thanks for the advice about pulse counting receivers piglet. I had heard of them, but they sounded like a newfangled digital thing rather than a ye olde device. I will look into that too.