# FM transmitter main output frequency

please tell me the output frequency of this circuit,its work and has about 10 watt power with using C2101 as output stage,thanks

It's working,and has high power in so far as I turn it on close to my notebook it's hanging,Also it has a fixed frequency.With a sensible frequency meter in about 3 meter distance from the circuit,It indicates 80,000255 hz and it dosn't change even when I touch the coils,This frequency has about 1 Km range even without aerial antenna,To the best of my knowledge I think maybe its a harmonic and the main and stronger frequency must be something else with regard to the supply current and TRs efficiency.Of course maybe this is not .The primary circuit does not have a frequency stability and it was useless actually without using crystal .I combine primary circuit with this one,using Lm386 as an audio amplifire,.Excuse me for grammatical mistakes. Here is the components value.In my circuit these value have the maximum output power,I conclude that the output frequency is the same 80 mhz most likely.With aerial, range is about
35 km ,Well,It should be the main output frequency,But please explain how does it work If possible. Thanks!

• Where did you find the circuit diagram and why is it partially blue? What are the values for nearly all components? – jippie Jan 25 '14 at 12:22
• House fm transmitter 88-108MHz at 4 Watt on this page looks more like the original circuit and the input stage makes more sense too. The accompanying text is not particularly giving much useful information though. diagram – jippie Jan 25 '14 at 12:38
• It is good practice to tell us where you find your circuits. It saves us from having to analyze the circuit ourselves. Apart from that it is fair for the original website to get the credit. circuitdiagram.org/crystal-controlled-fm-transmitter.html Also please use capitals at the start of a sentence, your text is really hard to read. – jippie Jan 25 '14 at 22:46
• Please please please use the normal rules of English capitalization, punctuation, and spacing (like spaces after commas and periods) to make your question easier to read. – The Photon May 2 '14 at 17:17
• Also are you using comma as a decimal mark or a thousands separator? I can't tell if you're asking about 80.000255 Hz or 80,000,255 Hz. You only make it more confusing when you start talking about "mhz" (millihertz). – The Photon May 2 '14 at 17:18

The blue colored input stage in your version doesn't make much sense. It probably doesn't work as expected at all, unless you expect the circuit to generate an unmodulated carrier wave.

It has an output power of 4 Watts

The output frequency the transmitter is adjustable from 88 to 108 MHz which is the FM band that is used for radio broadcasting.

Here is a more descriptive article, complete with Bill Of Materials, specifications and a more appropriate input stage.

http://www.smartkit.gr/fm-transmitter-4w-m.html

• The OP's circuit looks FM modulated to me, I think the varactor (BB102) is being used to pull the frequency of the 40MHz crystal. Although now I look further I think you're right and it's two circuits put together and probably wouldn't work at all. – PeterJ Jan 25 '14 at 13:21
• @PeterJ I don't see how the crystal can do anything but sit there blocking the signal. It is not going into resonance by an audio signal and the capacity for the varactor is minute with respect to the crystal. – jippie Jan 25 '14 at 13:24
• Yes I think you're right, it doesn't have a feedback path. I've seen the varactor modulation used before though, it doesn't need to pull the crystal far to FM modulate audio (the idea would have been from a 40MHz FM transmitter). – PeterJ Jan 25 '14 at 13:27
• The OP's circuit won't oscillate at all, but in general, varactor+crystal based FM modulators rely on frequency multiplication (sometimes several stages of it) in order to get sufficient deviation at the transmit frequency. – Dave Tweed Jan 25 '14 at 15:58