fm transmitter for 500m

If you want to know how the circuit works, read your attachment. :lol:

As far as range is concerned, if you want optimum results, you must make sure the receiver is set to the exact same frequency as the transmitter. The farther you are away from the correct frequency, the less range you have, and possibly no range at all.

Also, try another frequency that no one else is using. You might get better results.

and check your battery power too.

Construction techniques matter at 100 mHz. Did you build this on a breadboard, PCB or by some other means? A breadboard would be a bad choice - compact PCB or other compact techniques are better.

I'd attempt to measure the input current to the final amplifier stage (T2) and see how it compares to the author's statement that the output is 200 mw. You'd expect to see somewhat more than 200 mw input to the amplifier in order to expect 200 mw output.

Keep the regulations regarding this type of transmitter in mind.

The second stage, the amplifier, should be operating in class C, not A.

Deleted.Sorry

did you include the caps that show up as blank spots in the schematic? i had to enlarge the schematic to 150-200% to see them.

also the construction method (as someone already mentioned) is critical at 100Mhz, as is the coil construction. you will also want some way to measure the RF at the antenna connector... a 100Mhz scope or an RF "sniffer" would work, and a frequency counter would be helpful.

returning to the construction method, an inch (2.5cm) of wire is 23.2 nh, which has a reactance of about 15 ohms at 100Mhz. that's quite a substantial amount of reactance. and that's not counting parasitic capacitances between components and wiring. at 100Mhz, a lot of people prefer to use "ugly construction" because it keeps wire lengths very short, but it does take a bit of practice to do it right (and not short several connections in the process)

The sensitivity of the FM radio makes a huge affect on the range.

A cheap radio might pick up the signal across the street (30m) and be overloaded when only 1m away. When a cheap radio is overloaded then the signal appears all across the dial with very poor range.
A good radio (home stereo or car radio) might produce a range of 2km.

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