in search of a FM STEREO transmitter

[audioguru2]

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

 

[audioguru2]

Search Google for FM stereo transmitter. On page 6 there is a free link to the whole Silicon Chip project. The IC is surface-mount!Here's the schematic:

View attachment 36524

 

[EnigmaOne]

Of all things, I had trouble locating the page for the article...I finally tried "stereo FM micromitter" as the search key. It comes up as the only hit.
I'll hoover the article, graphics and associated downloads and stuff 'em in a zip archive for those who are interested in it.

 

[EnigmaOne]

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.

 

[rasOfir]

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 !!

 

[trigger]

rasOfir,

You have to try especially you build by yourself. I think no one can guarantee the quality.....
If you require high quality sound.... then.... don't put too much expectations.

 

[audioguru2]

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. 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.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

Hi Ras,
I've put in caps the good and bad points of the two transmitters to help your choice. The "South African" kit is much better but costs more. There are two kits listed in Google in the Micromitter search, but I can't see how they can charge $50 and $64 for just a $3 IC but they have a very nice case.

 

[audioguru2]

Hi Guys,
A position in the list of a Google search keeps changing by the number of hits it gets. Searching for the Silicon Chip project by stereo FM Transmitter was on page 6 yesterday, today it's on page 1 thanks to us guys.
EnigmaOne is correct, it is much easier to find by searching for stereo FM Micromitter and links to two kits for it are also there.

 

[rasOfir]

the EDM transmitter seems very good.. BUT...
it have a Frequency Response of : 20Hz - 15kHz... thats no good
it means u lose the higher sounds.. it lacks 7kHz to fill up the range.
and..
its quite expensive...80$ are allot of bucks.

maybe someone will publish the schematic for this, so we can all DIY it.
;D ;D ;D

 

[audioguru2]

Hi Ras,
Stereo FM and TV audio is limited to 15KHz (AM radios are lucky to get to only about 4KHz and few do). Any frequencies higher are supposed to be sharply rolled-off to avoid beating with the 19KHz pilot tone and avoid aliasing noises in the stereo multiplexing. The pre-emphasis (treble boost) that is applied to the audio prior to the multiplexing makes good filtering of high frequency audio even more necessary.

Look at the frequency response of the Silicon Chip project (or maybe I saw it on the datasheet for the BH1417). You can see audio frequencies rising above about 3KHz due to pre-emphasis, but the simple filter in the IC starts its roll-off at only about 10KHz. 15KHz from a radio listening to it would be down quite a few decibels. At 19KHz, where the response should be zero, the response is still fairly strong, about where it would be without pre-emphasis.
The poor performance of those filters and the lack of a high-pass-filter for the stereo subcarrier sidebands causes the project's high distortion.
BTW, the pre-emphasis on the datasheet and in the Silicon Chip project is for the Australian, New Zealand and European standard of 50us. In North America, the standard is 75us (big mistake, but hey, it came first!) so the treble boost is even more and the project will produce even more distortion. If you don't change it, a North American radio listening to it would sound rather muffled.

The EDM (South African?) kit uses a microprocessor that of course needs a program to run. Copying their program without paying for it would classed as theft of their copyright. So forget about DIY.
How good is its frequency response? Nobody knows. They only say the frequencies without mentioning how far down in level they are!

 

[rasOfir]

in the datasheet of the BH1417F
(http://www.rohm.com/products/databook/audio/pdf/bh1417f.pdf)

there is a scheme on page 2.
could someone look at it and see if its any good?
maybe its better than Silicon Chip project ?

i would go fo the SiliconChip project if u were not talking about distortion all the time - it is frightening

 

[audioguru2]

Hi Ras,
There is hardly any difference between the circuits. There is nothing changed that would affect distortion.
About the only differences I can see is that Silicon Chip couldn't find a Soshin FM bandpass filter so made their own with a capacitor and a couple of coils, and they changed a few parts in the PLL.
Since Rohm doesn't show any spec's (you have to request for them and maybe pay), I trust that the Silicon Chip circuit is better but will also have high distortion.

Earlier you were worried about frequency response and I replied that it starts rolling-off at 10KHz. I looked again and discovered that it is worse, the roll-off begins cutting only 6KHZ and 15KHz is down about 5dB, and using North America's pre-emphasis will be worse:

View attachment 36531

 

[rasOfir]

any chance to eliminate this d :-Xamn distortion somehow

 

[audioguru2]

Hi RAS,
As the expert explained, Rohm didn't use over-sampling to round-off the square waves of the multiplexing. Adding your own very complicated analog filters would reduce the distortion and of course switching off the stereo somehow and transmit in mono would eliminate most distortion.

 

[rasOfir]

i wasnt able tp reach the article..
maybe u can...

what about this one ?? :
http://www.siliconchip.com.au/cms/A_102010/article.html

 

[audioguru2]

Hi Ras,
Please don't underline your shortcut or it doesn't link.
If you enter Minimitter in a Google search, the project's link is on the 1st page and you can get the whole article for free!

As you can see by its spec's, this project also has high distortion that might be more when it transmits a higher level (they don't say how much modulation makes 200mV and 3% distortion).
The BA1404 is Rohm's 1st transmitter, the one everybody is laughing about:
1) It doesn't have a crystal nor PPL for its radio part so drifts its radio frequency all over the place. If your receiver doesn't have AFC and good receivers don't because radio stations don't drift, you will have to keep re-tuning. If your receiver is digital, you can't re-tune it and the transmitter's signal will come and go.
2) The square waves of the multiplexing aren't filtered so they interfere with its radio part.
3) The input audio frequencies aren't filtered so the high ones interfere with the 19KHz pilot. If you say the letter "S" into a microphone and transmit it through this circuit, your receiver will probably drop into mono. With music, it will keep switching between mono and stereo.
4) High distortion.
5) Etc.
Luckily, it isn't made anymore but lots of kits still have it.

 

[rasOfir]

hello again,
i m about to build this circuit, and i live in ISRAEL !
in another topic u wrote :
"The Micromitter is designed for Australia's 10mW RF power limit and uses their and Europe's 50us pre-emphasis standard. Check to see what your country's standards are"

could those be "wrong" ? i mean, if those standarts here in Israel are different should i make any chages to the circuit ?

does the "power limit" determines the transmission range ? if 10mW gives 20 meters does 100mW give 200 meters ? if so ... 10mW is enough for me as i want this transmitter only for in-house use !

i asked an expert here and he dont know of any pre-emphasis standart ! what difference does this "pre-emphasis" do ?

 

[audioguru2]

Hi Ras,
I hope that you like the Micromitter. Please let us lnow what it sounds like.

For the short distance between rooms of your house (you don't have a mansion?), its 10mW should be fine, it will probably go about 100m outside to a good FM receiver. 100mW will probably go 400m, 1W maybe 800m. Because the radiation is in a hemisphere, a single receiving direction gets very little and most of its power goes in the other directions.

I don't know Israel, you should find out its standards. Phone a radio station and ask their techie:
1) Is the FM broadcast band from 88MHz to 108MHz?
2) Do they use odd-numbered frequencies like 87.7-88.9MHz and 106.7-107.9MHz?
3) Do they use 50us pre-emphasis like Australia and Europe or 75us like North America?

If Israel uses different RF frequencies then the Micromitter won't work there, unless you have a 88MHz to 108MHz analog-tuned radio or a digital one where you can program the required frequencies.

Pre-emphasis is the treble boost that FM radio and TV stations use when transmitting. FM radios and TVs have the same exact treble cut to make the sound proper and reduce hiss. If Israel uses North America's 75us standard then the Micromitter's received sound will have too much treble. I think the article says what to change in the circuit to make it correct.

 

[Bryan11]

Hiya Guys,
The forum won't let me upload the zip file for the micromitter project as it's over a meg in size. but if anybody wants a copy of the siliconchip article then pm me and I can send it to you. I think it's a ripoff to charge just to look at an article from years ago. The kit is available from www.jaycar.com.au for $49.95 OZ.


Cheers Bryan1 ;D

 

[audioguru2]

Hi Bryan,
You don't need to upload Silicon Chip's article or pay for it. Just enter Stereo Micromitter (or Millimitter for the very old one) into Google and you are linked to the entire article for free. ;D