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    If you want to be independent of the local radio stations for testing VHF receivers, you need a frequency-modulated oscillator that covers the range of 89.5 to 108 MHz — but building such an oscillator using discrete components is not that easy. Maxim now has available a series of five integrated oscillator building blocks in the MAX260x series which cover the frequency range between 45 and 650 MHz. The only other thing you need is a suitable external coil, dimensioned for the midrange frequency.

    The MAX2606 covers the VHF band, although the frequency can only be varied by approximately ±3 MHz around the midrange frequency set by the coil L. The inductance values shown in the table can serve as starting points for further experimenting.
    The SMD coils of the Stettner 5503 series are suitable for such oscillators. In Germany, they are available from Bürklin (www.buerklin.de), with values between 12 nH and 1200 nH. You can thus directly put together any desired value using two suitable coils. If you want to wind your own coils, try using 8 to 14 turns of 0.5-mm diameter silver-plated copper wire on a 5-mm mandrel. You can make fine adjustments to the inductance of the coil by slightly spreading or compressing the coil.

    MAX2606 FM transmitter circuit diagram

    max2606 fm trasmitter

    The circuit draws power from a 9-V battery. The BC238C stabilises the voltage to approximately 4 V. Although the MAX2606 can work with a supply voltage between +2.7 V and +5.5 V, a stabilised voltage improves the frequency stability of the free-running oscillator. The supply voltage connection Vcc (pin 5) and the TUNE voltage (pin 3) must be decoupled by 1-nF capacitors located as close as possible to the IC pins. The tuning voltage TUNE on pin 3 may lie between +0.4 V and +2.4 V. A symmetric output is provided by the OUT+ and OUT– pins. In the simplest case, the output can be used in a single-ended configuration. Pull-up resistors are connected to each of the outputs for this purpose. You can use a capacitor to tap off the radio signal from either one of these resistors. Several milliwatts of power are available. At the audio input, a signal amplitude of 10 to 20 mV is enough to generate the standard VHF frequency deviation of ±40 kHz.

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    6 Responses to "MAX2606 VHF FM Transmitter"

    1. Sir ! How much is it’s range ?
      In C 6 what is “p” ?
      and can i use this transmitter At 88-108 MHz. ?

      • Sudip UPreti says: on March 19, 2011 at 2:36 pm

        yes you can use the transmitter in 88-108 MHz by changing the value of inductance- L1 as mentioned below figure.

        p in c6 indicates pico farad,
        1pf=1000nf or 1000000 micro farad.

        it is highly frequency stability transmitter with range of about 200-500 meter.

    2. OLADIPO, MUMIN O. says: on October 25, 2011 at 1:45 pm

      tanx 4 d circuit but hw do I adjust the range n hw can i build my own reciever with a pll

    3. where do i connect the mic

    4. hi

      can i reduce its range??

      like upto 30m???

    5. Is it possible to use USB as power supply? What needs to be changed in that case?

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