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FM Transmitter

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ivancho

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I would like to learn more about FM transmitters. All I can find are circuits that do not explain much on how stuff actually works. Anyone knows of any good sites that explains in detail how FM transmition works using a schematic perhaps. I've used google but I have not found anything, after hours of searching around useless websites.

Any good sites or books will be appreciated. Also the legality of making an FM transmitter for the 88Mhz range, low power in the US.

Thanks
 
FM is one of many modes used by amateur radio operators. American Radio Relay League (ARRL) publications cover that in detail. One of the Radio Amateur's Handbooks might contain what you need. Radio Society of Great Britain is another source of publications. I would like to think that a "radio engineering" handbook exists though the explanations may be hard to understand.

You might try the FCC website for info on transmitters. All of my publications contain text right from FCC however the publications are tailored to amateur radio. You will likely find that the transmitter power is very limited as will be the antenna, among other things. In general, I'd expect the limitations will keep the signal within the confines of a very small area.
 
If you get caught transmitting on the FM broadcast band in the US, first they torture you. Then they chop off your head. So don't. (Don't get caught.):D
 
Hours of searching? The first four search results for Frequency Modulation on google answer every basic question you could ask about FM modulation. Broadcasting radio frequency signals on any frequency at any power level on home made hardware or modifying consumer equipment is illegal unless you have a HAM license (morse code free nowdays) which require only basic RF and electronics understanding, though you're still limited to the frequencies and power levels if you're a HAM.
 
Just a couple of comments -

A. I think that in the US you can broadcast on some frequencies within some fairly severe limits. If you don't understand the limits don't do it. As a general rule those limits would keep the range to a few hundred feet. I don't think you are restricted to commercially built equipment.

B. As mentioned, it's illegal to modify commercially made consumer transmitting (and some receiving) equipment. Modification can be the addition of antennas or more involved changes. The stuff was approved for use as sold. Adding a home-brew antenna to a cell phone or wi-fy is not allowed. Modifying a scanner that's cell phone blocked so that it's no longer blocked is also illegal.

C. While the FCC does some monitoring it is more likely that illegal transmissions will bother someone else who will eventually track you down. Many commercial, government and hobby entities rely on radio transmissions and can be disrupted by inappropriate transmissions.
 
The websites that come up searching Frequency Modulation in google sure tells you how it works. But it is different from telling you how to buid a circuit that uses a PPL, or what to look for to tune it, etc. Perhaps someone can save me some time by recommending a site or book that goes a little bit more into detail on the actual design, and practical real life circuits than:

"Quote from Google search">>

Frequency modulation - Wikipedia, the free encyclopediaFrequency modulation (FM) is a form of modulation which represents information ... Frequency modulation is also more robust against simple signal amplitude ...
en.wikipedia.org/wiki/Frequency_modulation - 32k - Cached - Similar pages

Modified Frequency Modulation - Wikipedia, the free encyclopediaModified Frequency Modulation, commonly MFM, is a line code used by most ... MFM is a modification to the original FM (frequency modulation) scheme for ...
en.wikipedia.org/wiki/Modified_Frequency_Modulation - 15k - Cached - Similar pages
[ More results from en.wikipedia.org ]

FMIn frequency modulation the amplitude is kept constant and the frequency is ... Applet below shows a modulating signal in orange, the FM signal in red, ...
cnyack.homestead.com/files/modulation/modfm.htm - 3k - Cached - Similar pages

Frequency ModulationKnow the relationship of carrier frequency, modulation frequency and modulation ... FM radio uses frequency modulation, of course. The frequency band for FM ...
 
I googled on 'reactance modulator' and the first hit was **broken link removed**

Unless you knew quite a bit about FM you would not know to have done this so no criticism intended.

The internet/websites are a great thing but finding comprehensive collections of knowledge or instruction can be a challenge. The stuff that I think you would like is probably to be found in publications that have to be purchased or borrowed from a library, club, freind, etc. The site that I mentioned is clearly the result of some hard work that someone did for the benefit of others. Sometimes you get lucky and find that stuff. Sometimes you get what you got - a ton of hits and you can only sort thru so much of it.

A book that I'd recommend is one of the ARRL Radio Amateur's Handbooks. In there and other ARRL publications you'll find information on the theory. You'll also find some projects that have been completed by others. The problem - the stuff it tailored to amateur radio. Still, it will likely help you advance your knowledge of the subject.
 
Stevez,

Thaks you for the website, it has some really good information and in the way that I am looking for. I will try to check out the books, to see if I can gain some useful information.


Thanks,
 
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