I would like to build an FM transmitter on my own and I found a nice circuit that acts as a USB sound card to transmit low power FM signals. http://tipok.org.ua/node/35

My plan is to add another amplification stage with an additional device, commonly called FM Booster / FM Amplifier. There's one around fmuser.org that claims to amplify input signals from 0.2 to 0.4W up to 30W.

Unfortunately the output of FM Stick is only up to 0.1W. They use a transistor circuit around BFG541.

I really would like to use of-the-shelve parts only (like FM Stick does). At the same time I know that this will limit the maximum output of the circuit. But to what extent? What's the maximum RF output possible if one sticks to readymade parts?

I could not find any other circuit in the interweb, that does not rely on handmade coils.

Thanks in advance & Regards, Hans

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    \$\begingroup\$ This question appears to be off-topic because it is about something that is illegal in most countries. \$\endgroup\$ Aug 19 '14 at 14:42
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    \$\begingroup\$ @LeonHeller: It is not against EE.SE policy to entertain such questions. The OP may have a perfectly legitimate reason for what he's doing, and may be appropriately licensed to do so. Feel free to point out the regulatory issues, if you must. \$\endgroup\$
    – Dave Tweed
    Aug 19 '14 at 15:05
  • \$\begingroup\$ @DaveTweed - in addition to the regulatory issue, it is off topic because it is about using poorly specified grey-market consumer gadgets and explicitly in the OP's request not about the engineering design of such systems. \$\endgroup\$ Aug 19 '14 at 15:21

Hans, I don't know what regulations are in place in Germany or surrounding parts of Europe, but in the USA we're severely limited (by the Federal Communications Commission) in the amount of power we can broadcast on any frequency. You might want to see what similar regulation exists in your area before you try to broadcast more than about 100mW.

Using off-the-shelf parts, it's POSSIBLE to broadcast hundreds, thousands, millions of watts.


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