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help > FM Audio Transmitter Receiver modules

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GertJL

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Hi Group,
I am a new subscriber to this forum. I have read some of the articles and find the
info quite informative for me as a non-rf person. My background is digital design etc.

I have a requirement to transmit&receive audio (eg mp3/cd-player output)
over a distance of ~200m. I am thinking of using FM wireless technology because of Audio transmission quality, preferably tunable beyond the normal broadcast freq 88-108mhz.
My hands-on knowledge of RF is rather poor, so I am looking for 'glue-on' modules for both the Transmitter and Receiver. I believe nowadays the latest receivers make use of PLL to
ensure better tuning stability etc? Stereo transmission is not required.
Yes, I know one can buy commercial out-of-the box units like WireLess MicroPhones as a complete unit etc, however, I would like to use 'glue-on' modules which I can integrate into my own electronics for my application development. It is required that the Transmitter/Receiver set does not require re-tuning in the field, if possible. Further it will be good to have preset channels eg A,B,C. If the Receiver/Transmitter has an uProc Interface to assist with the tuning/ setup of the units, it will be great.

If the FM Receiver has an integrated Audio Amp ~3-5W built-in, even better.
Yes, I realise that one can buy commercial FM Radios of the shelf, however, I wish to source
modular solutions which I can integrate into my application.

Operating Voltage, well, I don't know, 3.6-10Vdc?

I am not sure whether this is poor question : What RF power rating should the FM Transmitter
be to reach definitely 200m omni-direction distance. Any particular spec for the sensitivity and tuning stability-repeatability from power-recycle of the Receiver / Transmitter?

If modular-sets like this is not economical available, I would like to investigate what current state of the art type FM Transmitter/Receiver ICs are available to build-up from scratch, to minimize my RF 'tuning' and experimentation, with low Inductor-count, since I do not have RF R&D Equipment.

Can any of you assist, recommend or want to supply modules like this?
It is low volume though.

I may not have given enough info due to my lack of knowledge, so, please feel
free to ask relevant questions pertaining to this matter.

Thanks for reading, I appreciate your sensible comments and feedback.

Regards,
Gerhard
Cape Town
South Africa
 
Hi Gerhard,
welcome to the forums

depending on the what the path is like over that ~ 200 metres somewhere ~ 50 to 100mW should be ample to ensure a good signal
and that low power level would keep you below the requirements to have to get an operating licence. ( dependant on the specific rules in SA.

So what would the general path be like ? lots of trees? lots of buildings ? or predominantly line of sight? or a good mixture ?

There are some good low power units that you could use as a starting point like the ones that can transmit you MP3 player to the car 88-108MHz band receiver. These are usually just a few milliWatts and have a PLL/Synthesised transmitter for stability. With the addition of a small amplifier you could bring their output up to ~ 100mW quite easily with a minimum of construction, knowledge there of or fancy test equip. All with fall into your abilities of not being a RF person :)

A GALI-39 or a GALI-84 MMIC will fit that requirement :)

Dave
 
Hi Dave,
Thank you very much for welcoming me and your valued input. I looked at the Mp3 player FM transmitters,
however, I would rather like to source tx/rcv modules which I can plug-in, glue-on my my application,
which will be low volume production of equipment used in an industrial market. So, I had a quick look
at the your recommended components. I contacted a company Mini-circuits for more info.
As I have indicated, I would prefer to buy-out units at this time. Re geographic deployment it, will be deployed in
an around a factory-perimeter, mostly outsid, oopen air, thus partly open space, as as you pointed out, mixed geography. I would like to be able to set the operating frequency beyond the 88-108Mhz.
Many thanks for your valued input.
Regards,
Gerhard
Cape Town, South Africa
 
Hi Dave,
Thank you very much for welcoming me and your valued input. I looked at the Mp3 player FM transmitters,
however, I would rather like to source tx/rcv modules which I can plug-in, glue-on my my application,
which will be low volume production of equipment used in an industrial market. So, I had a quick look
at the your recommended components. I contacted a company Mini-circuits for more info.
As I have indicated, I would prefer to buy-out units at this time. Re geographic deployment it, will be deployed in
an around a factory-perimeter, mostly outsid, oopen air, thus partly open space, as as you pointed out, mixed geography. I would like to be able to set the operating frequency beyond the 88-108Mhz.

So how long do you expect to stay in business manufacturing illegal equipment?. And presumably your users will take legal action against you when they are prosecuted.

I would STRONGLY suggest you contact the authorities in your country before you decide to break what are serious laws in most civilised countries.
 
I am not sure whether this is poor question : What RF power rating should the FM Transmitter
be to reach definitely 200m omni-direction distance. Any particular spec for the sensitivity and tuning stability-repeatability from power-recycle of the Receiver / Transmitter?
Depending on the local environment, a few 10s of milliwatts would be plenty.


If modular-sets like this is not economical available,
I have never seen for sale a "radio voice module" in the same sense that a "radio data module" is available as an off the shelf component.


I would like to investigate what current state of the art type FM Transmitter/Receiver ICs are available to build-up from scratch, to minimize my RF 'tuning' and experimentation, with low Inductor-count, since I do not have RF R&D Equipment.
Not a good idea to just pick some radio technology and adapt it for some other purpose.
RF spectrum is highly regulated for very good reasons which may not be immediately obvious to the casual observer.

Nigels words in the post above may sound a bit harsh, but they are the truth.

JimB
 
Hi JimB,
Thank you for your valuable input.

I am up to date with the current RF regulations in my country.
There are manufacturers, in Canada, which have commercial 433Mhz fm audio components (tx,rcv)
however, at quite a pretty penny.

Regards,
Gerhard
 
Hi JimB,
Thank you for your valuable input.

I am up to date with the current RF regulations in my country.
There are manufacturers, in Canada, which have commercial 433Mhz fm audio components (tx,rcv)
however, at quite a pretty penny.

Regards,
Gerhard

I would be a bit wary of that too Gerhard,
the 433MHz allocation is for intermittant transmission low power data transmitters and receivers and not for higher power contineous voice/music transmissions. 433MHz is also almost at the bottom end of the amateur radio 70cm band allocation and those guys would not be impressed with a 433MHz music signal screwing up their repeaters etc.
There is another band in the 300MHz area, not sure if thats like the 433MHz one for data only or not, it may be worth exploring.

I suspect tho that your only choice would be within the 88 - 108 MHz band where music transmissions are already allowed by low power unlicenced units. If you havent already, you would need to consult your local authorities to see what the max power level is allowable before a licence is required.
Moving just up from 108 MHz and you have the aviation freqs and they go right through to ~ 135 MHz then you have weather satellite downlinks.

you are probably going to find it quite difficult finding off the shelf gear (modules) to purchase which is why I was suggesting the path I did

cheers
Dave
 
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