Basic FM transmitter

[alec_t]

Power supply ripple of only 100uVpp will produce about 200kHz of frequency deviation

So presumably a 100uV drop in battery voltage would produce a similar frequency deviation. Assuming an approximately linear deviation of frequency with supply voltage then a 10mV drop (likely after only a short time of battery use, or even as temperature changes) would shift the frequency ~ 20MHz !!! Hardly a desirable feature (and of dubious legality)!

 

[audioguru]

So presumably a 100uV drop in battery voltage would produce a similar frequency deviation. Assuming an approximately linear deviation of frequency with supply voltage then a 10mV drop (likely after only a short time of battery use, or even as temperature changes) would shift the frequency ~ 20MHz !!! Hardly a desirable feature (and of dubious legality)!

His extremely poor quality FM transmitter is very simple and very cheap.
Adding a simple and inexpensive low-dropout voltage regulator IC like in my FM transmitter will make it much more stable.
Adding a simple and inexpensive RF amplifier to its output like in my FM transmitter will make its frequency stable when something moves toward or away from its antenna.
Adding pre-emphasis will make it sound much better for people with normal hearing (maybe he is deaf?).

He doesn't care if his FM transmitter is illegal. Maybe there are no laws about causing interference in his country?

 

[bloki]

alec_t, yes it's true. Because of that transmitter practically can not be used on PLL receivers but only on old type with continious change of receiver frequency.

 

[audioguru]

This FM transmitter is practicaly capable of only telephone voice quality. Thus it needs no pre emphasis so as all variants of this transmitter does not have it.
audioguru is exaggerating all the time and is well known by his arrogance.

Then why is he making a transmitter for the FM broadcast band when all he needs is muffled and tinny ham radio or AM broadcast band quality??

 

[bloki]

audioguru, your FM transmitter is only much more complicated nonsense and it is not legal allso. So better stop spaming.

 

[metal freak]

i want to transmit my stereo audio signal through fm band.......between two terminals.....either transmitter or receiver is optional....i mean i can buy one of them...........which is more fisible to make...transmitter or receiver??pls help out quickly!!with schematics if possible!

 

[KJ6EAD]

Metal freak, you should start a new thread instead of hijacking this one, even if it has degenerated into an entertaining argument.

The Indian Ministry of Communications and Information Technology, Department of Telecommunications, Wireless Planning & Coordination Wing requires a license for low power community non-commercial FM stations similar to the U.S.
**broken link removed**

 

[audioguru]

i want to transmit my stereo audio signal through fm band.......between two terminals.....either transmitter or receiver is optional....i mean i can buy one of them...........which is more fisible to make...transmitter or receiver??pls help out quickly!!with schematics if possible!

Radio parts are difficult to find today. You need to know how to layout and connect the parts so they work properly.
In the USA you can buy an excellent FM stereo transmitter kit from Ramsey. I posted its assembly instructions here yesterday.
In Australia and New Zealand you can buy an excellent low cost FM stereo transmitter Kit. Here is its schematic (Micromitter).

Unlike these guys in India who make junk toys I think you want pretty good quality.

I don't know any half-decent modern kit for an FM stereo radio. Buy a radio.

 

[Ziddik]

audioguru, we all hav normal hearing (maybe u r deaf?) and get a clear sound output from the transmitter(not like AM,telephone!) and this extremely simple circuit doesn't need ur"pre emphasis" and "Trouble boost", maybe ur transmitter sounds like an unstable AM radio or u must be deaf or cleaning ur ears may be solve ur "pre-emphasis" and "trouble boost" problems

 

[Ziddik]

the "HORRIBLE" stereo transmitter circuit he posted will not last more than 2 or 3 days as the 9v battery drains quickly (may be u might need buy battery everyday) and the output power will be very slow as there is not an rf amplifier in output,..the 7805 used in this circuit will waste voltage n its more complicated and u can't use a powersupply as it will generate hum and distortions, the easy and cheap way is use a normal well designed transmitter circuit.

 

[KJ6EAD]

Transmitters based on the ROHM BH1415 and BH1417 ICs are quite good.

 

[audioguru]

audioguru, we all hav normal hearing (maybe u r deaf?)

No. We all do not have normal hearing and I am not deaf since I hear up to about 16kHz (pretty good for a 65 years old).
Some members here were talking about making hearing aids. Colin55 who sold 30,000 FM transmitters without pre-emphasis mentioned that he is deaf and cannot hear high audio frequencies. His FM transmitters and his hearing aid circuit produce no high audio frequencies.

We get a clear sound output from the transmitter(not like AM,telephone!) and this extremely simple circuit doesn't need ur"pre emphasis" and "Trouble boost", maybe ur transmitter sounds like an unstable AM radio or u must be deaf or cleaning ur ears may be solve ur "pre-emphasis" and "trouble boost" problems

I guess you never learned anything about FM broadcast band radio. In Google there are many sites that explain about pre-emphasis in all FM broadcast band radio transmitters and de-emphasis in all half-decent FM radios. Maybe you have a cheap FM radio that does not have de-emphasis.

Here is a good explanation but the demo without pre-emphasis has an error: https://www.claessonedwards.com/index.php?option=com_content&view=article&id=72&Itemid=89 The demo without pre-emphasis also is without de-emphasis in the receiver.

In North America FM radio stations and radios use 75us emphasis which begins at 2133Hz. Without pre-emphasis then a radio with de-emphasis will produce 2133Hz at -3dB, 4266Hz will be -6dB, 8532Hz will be -12dB and 17kHz will be -18dB just like or worse than a treble tone control turned all the way down. This is worse than a telephone and about the same as a cheap AM radio.

Since your FM transmitter does not have pre-emphasis then its sound played on a normal FM radio that has de-emphasis will sound like your stereo with its treble tone control turned all the way downn, very muffled with high audio frequencies attenuated.

 

[mvs sarma]

Radio parts are difficult to find today. You need to know how to layout and connect the parts so they work properly.
In the USA you can buy an excellent FM stereo transmitter kit from Ramsey. I posted its assembly instructions here yesterday.
In Australia and New Zealand you can buy an excellent low cost FM stereo transmitter Kit. Here is its schematic (Micromitter).

Unlike these guys in India who make junk toys I think you want pretty good quality.

I don't know any half-decent modern kit for an FM stereo radio. Buy a radio.

hi A G,
one person called 'AN920" has analyzed this Silicon chip design, based in application note of BH1417F, and did suggest few mods. Perhaps you too would remember that as it it was from another site, where we were all members. perhaps they are worth consideration and these kit sellers could have a better kit thoroughly checked by eminent persons like you. i stiil have a copy of those mods. as th site was damaged most of its stuff.

 

[audioguru]

Hi Sarma,
I didn't save the mods to The Micromitter because it is now fairly old and I will never build one since I don't need one. If I ever do need one then I will buy one of the many excellent FM stereo transmitters available for transmitting an MP3 to a car radio.

 

[carbonzit]

In this thread we have the ignorant (Ziddik) battling the arrogant (Audio McDuck).

Faced with this choice, I think I'll side with the arrogant. At least he knows from whereof he speaks.

Other than to say that, I'm outta here.

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

By the bye, regarding the legality issue that keeps rearing its ugly head here:

It's pretty much a moot point. (Well, so long as Ziddik's little toy transmitters don't cause interference to other people's broadcast band radios.)

Yesterday I helped a friend install a sound system, including a wireless microphone. We basically set up a small FM transmitter/receiver. This is no more illegal than a wireless telephone, again assuming that it causes no interference with anyone else's enjoyment of the FM band. So please let's drop the phony legal/illegal stuff.

 

[4pyros]

How about this one?
**broken link removed**
The chips are still avalible!
Andy

 

[4pyros]

look here;
https://www.electro-tech-online.com/threads/fm-transmitter-please-help-me.113346/
From almost a year ago and still going.

 

[4pyros]

Here are the mods-
https://www.electronics-lab.com/forum/index.php?PHPSESSID=g2pnq88gcrs3fv4hpvafd76nm3&topic=11519.0

 

[carbonzit]

The LTspice sub-thread

cz,
Look at this extract from the web page link.
**broken link removed**

Its explains the use of the 'maximum time step' and what it means.

Eric, with all due respect, it explains something about how to use the time step. It does not, however, explain what the timestep means. I still don't know exactly what this parameter does. What that tutorial says, basically, is "play with the step parameter until it works for you". Not good enough. I'd like to know what it does and how it works so I can tweak it in an educated manner, rather than just throwing darts at the dartboard.

Isn't there any better documentation of this very useful piece of software anywhere out there on the web?

 

[Ziddik]

u r the most ignorant person here after AG, u both have never made an fm transmitter(finally i have to think so) because u both talk like u failed many times to make an fm transmitter! learn the basic sides of fm transmission first and babble of it will make a sense, and AG he thinks we are all deaf like him (maybe the cheapest radio he using not have a quality speaker! Or he got subwoofer output through his cheap radio speaker?) and his poor quality fm transmitter (he owns a"preemphasis" and "trouble boost") is more complicated with a bunch of unusual componets! Its natural that he is jealous of my circuit as it works well without his "preemphasis" and "trouble boost," and carbonzit u better make a transmitter before posting sensless and racial comments! And dont NEVER forget to add Audioguru's "Holy " "PREEMPHASIS AND TROUBLE BOOST" in it!