stereo Transmitter

[MNA]

http://home.telkomsa.net/jeanward/fm_stereo.htm
can this stereo encoder be connected to audioguru fm tx?..... Why?..what's the theory?...

 

[audioguru2]

http://home.telkomsa.net/jeanward/fm_stereo.htm
can this stereo encoder be connected to audioguru fm tx?..... Why?..what's the theory?...

My FM transmitter doesn't have a wide enough audio bandwidth for stereo. Its audio response drops at around 15kHz but stereo needs a response up to 53kHz.

The circuit you have is basically copying what is inside an inexpensive BH1415 Rohm transmitter IC. But your circuit uses an inaccurate 555 oscillator instead of the necessary crystal oscillator in all other stereo transmitters. It also uses a separate RF transmitting section.
The BH1415's RF frequency drifts all over the place but their BH1417 FM stereo IC transmitter fixes it with a crystal controlled frequency synthesizer circuit.
In Google, you can search for and see Silicon Chip magazine's Micromitter project that uses Rohm's BH1417 IC. If you need more range then you can remove its output attenuator and/or add an RF amplifier transistor.

 

[chief11]

The google trick with Silicon Chip doesn't work for me anymore, I think they may have fixed the bug.  :-[

I do have a subscription to the mag, but it was nice to get past articles from before I started my subscription.

 

[MNA]

Hi audio,
I think before moving on ....I should see the datasheet of BH1415.....I tried on google but surprisingly didn't get to one....If u have found it's datasheet plz supply me the link....
Silicon Micromitter IC is surface mount ....

I know using IC will make it easy,but I think that not using IC will help in understanding many concepts.....as you know I am new to the subject....Anyway, I would like to see the BH1415 dataheet....
thanx

 

[MNA]

As far as the datasheet is concerned, I have found it....

 

[audioguru2]

Here is a pretty good article about the theory of FM stereo with some links at the bottom about Rohm's older ICs:
http://members.tripod.com/~transmitters/stereo.htm

 

[MNA]

thanx Audio..I am going through the article...it's good.
you said The BH1415's RF frequency drifts all over the place ...What does this mean??

 

[audioguru2]

you said The BH1415's RF frequency drifts all over the place ...What does this mean??

The RF frequency is not stable, like "toy" FM transmitters and changes with temperature change, supply voltage change and when something gets near its antenna.

The web has nasty stories about cheap kits that use Rohm's BH1404 FM transmitter IC that also drifts. Some countries do not allow FM transmitters that do not have their RF frequency crystal controlled.

Many "digital" FM tuners do not detect an RF frequency that is drifting.

 

[MNA]

Audio,I'm really not getting what is going on.....where's the problem??....Is this due to 555......Is there something to be done with PLL???......what to do and what not.....Explain me plz :-\

 

[audioguru2]

Audio,I'm really not getting what is going on.....where's the problem??....Is this due to 555......Is there something to be done with PLL???......what to do and what not.....Explain me plz :-\

A 555 is not anywhere near accurate enough as the 76kHz stereo oscillator for a BH1415. The datasheet for the BH1415 mentions using a very accurate 76kHz crystal instead of a 555.
The stability of the RF section of the BH1415 is also poor.
The newer BH1417 uses its crystal's accuracy for both.

 

[MNA]

Sir,I m confused....1) U r talking about RF section..do u mean FM transmitter section or any section in the stereo encoder?.....2) I think that 555 timer can be replaced without any difficulty,am I right?...3) I don't have BH1417 datasheet with it's internal diagram....

 

[MNA]

I was searching about the stereo encoders and got this ....Well it uses the crystal.....About RF section,I'm absolutely not clear about what u r pointing at.......It is giving MPX output ,Is it going to be connected to the previous fm transmitter crkt  or something else would have to be done?.......thanx.
I was unable to attach the crkt..
http://renaud.cerrato.free.fr/download.html
I'm talking about the stereocoder on this link at the bottom...
I'm sorry for the inconvenience but i can't attach it and u know the reason...

 

[audioguru2]

I am also confused about Rohm's new FM stereo transmitter ICs because their datasheets don't have any details. They all appear to use a 7.6MHz crystal with a PLL as a very accurate RF frequency synthesizer and the crystal's frequency is divided for very accurate stereo frequencies.

The stereo encoder circuit that you posted from Telkomsa has an inaccurate 555 oscillator, is missing pre-emphasis (treble boost) for both inputs and very sharp lowpass filters. Rohm's new ICs have them.

Your latest post at Renaud is for an RDS encoder. I didn't see a stereo encoder there.

 

[MNA]

Hi Audio,
I found the Stereo coder at the bottom....I've attached it...

STEREO_schema.zip

 

[MNA]

Well Audio, I was reading some articles to understand the functioning....

"Oscillator Types:

1. VFO (Variable Frequency Oscillator) - An oscillator whose output frequency can be changed by adjusting a variable inductor or variable capacitor.

2. VCO (Voltage Controlled Oscillator) - An oscillator whose output frequency is controlled or changed by an application of external voltage. VCO uses varicap diode that changes the capacitance as different levels of voltage are applied.

3. PLL (Phase Locked Loop) - A circuit that synchronizes a frequency of VCO with a frequency of a reference oscillator by using a comparison of phase between the two signals. PLL takes a frequency of VCO, divides it into a lower frequency which can be compared with a stable reference oscillator. Then amplifiers are used to send an appropriate voltage back to the VCO to keep the desired frequency stable.

4. Crystal Oscillator - Oscillator that uses a crystal to generate a frequency."

1.Which one is preferred in which conditions.......(i.e. voice fm tx,stereo fm tx....)?

2. If I'm right the transmitter crkt is based on VCO....and u r saying it should be crystal oscillator??? Is this crkt going to give me nothing or is it worth trying?

3. as far as stereo encoder is concerned,the second one looks to me better,as it is using crystal...what do u say ?

4. Can I transmit voice with a stereo transmitter???...by grounding L????

I started this topic without any knowledge about transmitters...but it seems to me that I'm getting some.Thanx for you helping.

 

[audioguru2]

The stereo coder uses a lot of parts, doesn't it?

 

[MNA]

yeah it is...but the previous one uses 555.....and I didn't get any other crkt....apart from parts what else r your views about the crkt....Actually,I know it will be a lot easier to use Bh1417 ic....but I m trying to get it in the other way....ok not using ic will not produce good results,but I think atleast something will be produced at the end????? It will help in understandings much....

 

[MNA]

Audio,many questions coming in my mind....so I'm just posting them from time to time...hope u or anyone else will reply them at his convenience.....If a crystal controlled transmitter may be used,then will it get better? ..... the problem is I don't know which transmitter can be used as the circuit page  mentions about some input ....

 

[MNA]

I've referenced the first  circuit from which I started the topic,in my previous post.....I thought my previous post  was a little confusing ...