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in search of a FM STEREO transmitter


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i listen to music on the net but my hi-fi is to distant from my computer too run cables between !
so i want to build me a radio FM transmitter to plug into my sound card headphones jack !!!
i've found allot of schematics on the net, but..
due to my lack of knowledge in electronics i cant choose the best !!

PLEASE HELP ME and point me to the best project !!


i need no more than 50 meters of trasmission but it MUST be in very good quality .
the parts must be as common as possible with no hard-to find.
it should be operated by batteries.. best = 1.5v but also possible 3v and 9v.
of course it MUST be a stereo.
posibility to change "station" (=fm frequency).
with no frequency loss on the way = sound received must be exactly the same as "sound in"
no drifts of the frequency.
the complete hearing range (20k - 22m) must be transmitted.

oh yes.. it should be simple to build as i m only a hobbeist

thanx

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Hi rasOfir, and welcome.

You really need to know what you're doing to take on such a project.
I have made an FM stereo transmitter using the (BA1404) FM stereo transmitter IC, for the same reasons you want to, it does every think that you want, well almost. the transmitted sound quality is not all that flash, it was intended to transmit to my stereo about four metres away, my stereo must be very fussy on the signal it likes, keeps cutting in and out, however my clock radio that is at the other end of the house, has no problems picking up the signal, my car stereo does even better I can still hear music playing from my computer as I drive down the road, yet my stereo four metres away just won't have it.

There are better quality FM stereo transmitter IC available, I wouldn't recommend the one I tried using.

If I was going to have another go at making one of these stereo transmitters, I would go for a good quality kit.

You may have better luck than I did, but from my experience it isn't an easy thing to do.

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Good find rasOfir :D,

I'll have to take on that project as well, when I get the chants :).
There's a lot of FM transmitter projects out there, yes that can be difficult choosing the right one ???.

Have a look in the projects, you might find something to your liking( http://www.electronics-lab.com/projects/rf/index.html)

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Hi Guys,
The simple NJM2035 stereo encoder circuit is missing very important filters in its audio inputs that keep high frequency audio from beating with its 19KHz stereo pilot tone. The pre-emphasis amplifies the problem where the beats end up as interfering audio noises and messes-up the stereo 23KHz-53KHz stereo sidebands. Additional filters are needed for the stereo sidebands.
Simple filters have been shown (maybe by NJM) but they cause phase-shift which reduces stereo separation and are missing an important notch at 19KHz.
Search Google for FM Transmitter and you'll find many articles about it. One expert has reviewed many kits and has tweaked the NJM2035 to perform fairly well. He laughs at the BA1404 circuit Dazza used which is still available in many kits.

Don't use a simple "toy" FM transmitter circuit. They drift their frequency all over the place! If your receiver is digital, it will reject it by muting, that was probably Dazza's cutting problem.

In the Google articles you will find a report about an excellent FM stereo transmitter kit that uses a frequency synthesiser for stability, a tuned-frequency display and has all the required filtering. It is about $60.00US. I think it comes from South Africa.

In stores you'll find "adapters" that transmit MP3 players to car FM radios. There are some very good ones like Sony has but their range is short. Maybe the range can be extended by adding an antenna.
Watch the quality. My son bought a cheap Chinese one to use his MP3 player with his car radio. It turned out to be mono-only and sounds horrible!
Good luck with your search.

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Hi Ras,
Yes, FM stereo transmitters are complicated. :o
If you want the transmitter to drift all over the place and sound lousy, spend only a few bucks for a few parts.
If you want quality, build the $60.00US kit that is probably the least expensive quality FM stereo transmitter available. The little factory-made adapters are also expensive for quality ones but don't have enough range. ;D

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Hi Ras,
A search in Google for FM Transmitter showed hundreds of good inexpensive stereo FM transmitter kits, including a few that plug into a PC's PCI slot. Their frequency and power are programmed with the computer to cover your house or your whole community.
I couldn't find the South African one again, but it's there.
Google also showed many "cheap" transmitter kits that use the poor BA1404 and unfiltered NJM2035 ICs.
Look yourself, you'll find a nice one.

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Hi Ras,
I am sorry that I am not an expert on stereo FM transmitters to help you choose. I just read their spec's and reviews. (And rap or rhyme about them!) ;D
Since you don't know the very basic spec's of stereo FM radios or transmitters and are not a master, maybe you should just run some wires instead of becoming a broadcaster. ::)


Dazza already explained his bad experience with a BA1404 circuit and doesn't recommend it, and the article I posted has an expert laughing at it. :'(
I suggest that you think about it a bit, then maybe you'll realise that it is difficult to choose a good kit. (It does sound like rap, doesn't it?)

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how can i know the best one ?
not looking on the price but on the specs. of the kit...
what am i looking for ?


The South African kit audioguru is talking about.


for example:
what "Channel separation"?


In a transmitter?

Well I suppose if it's transmitting on more than one frequency, but normally this means the difference in frequency between two channels.


what "Input sensitivity"?


How well the transmitter responds to the input signal from the head phone jack.

You need to check it's simalar to the output of your system, 20mV p-p from a head phone jack into a system designed to accept 5V p-p from a speaker output will underdrive it and make it to quiet, 5V p-p into a system designed for 20mV will overload it causing distortion and possible damage.

Impedance is also a factor you should consider, a headphone jack will work with a load anywhere between 8 and 64ohms and a loud speaker output is ok for 4 to 16ohms. But as a general rule you should match the impedance as closely as possible.


what "s/n ratio"?


s/n stands for signal to noise ratio, its the ratio of the wanted signal to the unwanted noise in a system, basically the higher the number the better.

PLL or not ?

PLL stands for Phase Locked Loop - a method for producing an exact frequency or allowing a receiver to lock on to a signal. PLL transmitters and receivers are better than normal ones.

See this link for more info on PLL: http://www.uoguelph.ca/~antoon/gadgets/pll/pll.html

ba1404 or not


The BA1404 is the stereo FM transmitter IC used in many kits.

how can i know GOOD QUALITY ??


By reading the specfication, hopefully I've given you a few hints as to how to interpret it.
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Hi Alun,
Channel separation in a stereo transmitter refers to the maximum dB difference between the left and right audio channels. The necessary filters reduce the separation so a left channel sound would also be heard on the right and usually sounds very distorted on the wrong channel, reduced by the amount of separation, and vice-versa. High-tech stereo transmitters use over-sampling by Digital-Signal-Processing (DSP) to filter very sharply, accurately and without phase-shifts. Therefore they have excellent stereo separation (about 60dB). The lower the spec'd dB separation number, the closer the sound is to mono with a lot more distortion.

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Hi Guys,
I found what I think is the "South African" stereo FM transmitter kit on Google. Their description and spec's of this product is detailed (many pages) and good. I'm curious that I can't find their address anywhere on their website, but they mention shipping by US-postal service. Their website ends with ".ZA" which is the country of Zambia, isn't it? http://home.global.co.za/~edm1/

Rohm Corp., the manufacturer of the lousy BA1404 stereo FM transmitter IC has some new ones that correct problems with that old one. Their BH1417 has a Phase-Locked-Loop for solid frequency stability. Silicon Chip (Australian magazine for electronic hobbiests) has a project for it showing a DIP IC. Rohm's website says it is surface-mount only. Go figure!
The expert that I mentioned before tested it and reports that its stability is excellent but its distortion is very high.
Silicon Chip's project:
http://www.siliconchip.com.au/cms/A_30378/article.html

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Hi Alun,
Channel separation in a stereo transmitter refers to the maximum dB difference between the left and right audio channels. The necessary filters reduce the separation so a left channel sound would also be heard on the right and usually sounds very distorted on the wrong channel, reduced by the amount of separation, and vice-versa. High-tech stereo transmitters use over-sampling by Digital-Signal-Processing (DSP) to filter very sharply, accurately and without phase-shifts. Therefore they have excellent stereo separation (about 60dB). The lower the spec'd dB separation number, the closer the sound is to mono with a lot more distortion.


Of course!

I feel a bit stupid now,:D channel separation is also a specification of op-amp chips with more than one op-amp - it's basically a measure of cross talk.
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Hi Guys,
I found what I think is the "South African" stereo FM transmitter kit on Google. Their description and spec's of this product is detailed (many pages) and good. I'm curious that I can't find their address anywhere on their website, but they mention shipping by US-postal service. Their website ends with ".ZA" which is the country of Zambia, isn't it? http://home.global.co.za/~edm1/


Zaire is sticking in my mind as the country for the tld "ZA" but I certainly could be wrong on that count.

Anyway...The order processing is routed through edmdesign.com, so you can:

[email protected][example.user]# whois edmdesign.com

Whois Server Version 1.3
   Domain Name: EDMDESIGN.COM
   Registrar: DOMAINDISCOVER
   Whois Server: whois.domaindiscover.com
   Referral URL: http://www.domaindiscover.com
   Name Server: NS1.DOMAINDISCOVER.COM
   Name Server: NS2.DOMAINDISCOVER.COM
   Status: ACTIVE
   Updated Date: 02-sep-2004
   Creation Date: 02-sep-2004
   Expiration Date: 02-sep-2005

>>> Last update of whois database: Tue, 1 Feb 2005 07:49:08 EST <<<

The Registry database contains ONLY .COM, .NET, .EDU domains and
Registrars.

Registrant:
   D.Maree
   27834 Canyon Hills Way
   Murrieta, CA 92563
   US

   Domain Name: EDMDESIGN.COM

   Administrative Contact, Technical Contact, Zone Contact:
      D.Maree
      27834 Canyon Hills Way
      Murrieta, CA 92563
      US
      951-600-9922
      http://www.emailaddressprotection.com [email]

   Domain created on 01-Sep-2004
   Domain expires on 01-Sep-2006
   Last updated on 01-Sep-2004

   Domain servers in listed order:

      URL1.BUYDOMAINS.COM
      URL2.BUYDOMAINS.COM

and that should give you the contact information you crave.

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Sorry about Silicon Chip asking for money to see their project. I don't know how but I got in through Google for free and read the whole thing! I should have copied it 'cause now other forums are also asking about it. :-[

What was Zaire called when I went to school? Belgian Congo? Zambia was probably called Northern Rhodesia. ???
He, he. Most countries over there changed their name as they became independent. ;D

Somebody e-mail EDM Design to see if that transmitter kit is made in Africa or California. Who, me? I don't need one, I still have the FM transmitter I made more than 40 years ago with germanium transistors! ;D

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Somebody e-mail EDM Design to see if that transmitter kit is made in Africa or California. Who, me? I don't need one, I still have the FM transmitter I made more than 40 years ago with germanium transistors! ;D

Lucky guy...my germainum plant died a few years back. Can't do nuttin' with it.

I tried uploading the zip archive (only 2MB) but the board is fussin' at me about it. Anyway, if'n you want the article in its entirety (downloads and all), let me know.
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are you talking about this :
http://www.siliconchip.com.au/cms/A_30378/article.html

is this the experts recommendation ??
should i try and build this one ?
did any one tried it ?
is it up to me standarts (see the first post on this subject) ?
is the 'south african' better then this ?

sound quality is very important to me, i dont want ANY drifts/distortion/hearing-leftside-on-rightside !!

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