Long range FM transmitter CircuitThe ability achievement of best of these circuits are actual low because no ability amplifier stages were incorporated.
The transmitter ambit declared actuality has an added RF ability amplifier stage, afterwards the oscillator stage, to accession the ability achievement to 200-250 milliwatts. With a acceptable analogous 50-ohm arena even antenna or multi-element Yagi antenna, this transmitter can accommodate analytic acceptable arresting backbone up to a ambit of about 2 kilometres.
The ambit congenital about transistor T1 (BF494) is a basal low-power variable-frequency VHF oscillator. A varicap diode ambit is included to change the abundance of the transmitter and to accommodate abundance accentuation by audio signals. The achievement of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) forms a VHF-class A ability amplifier. It boosts the oscillator signals� ability four to bristles times. Thus, 200-250 milliwatts of ability is generated at the beneficiary of transistor T2.
For bigger results, accumulate the ambit on a good-quality bottle adhesive lath and abode the transmitter central an aluminium case. Shield the oscillator date application an aluminium sheet.
Coil ambagious capacity are accustomed below:
L1 - 4 turns of 20 SWG wire abutting anguish over 8mm bore artificial former.
L2 - 2 turns of 24 SWG wire abreast top end of L1.
(Note: No amount (i.e. air core) is acclimated for the aloft coils)
L3 - 7 turns of 24 SWG wire abutting anguish with 4mm bore air core.
L4 - 7 turns of 24 SWG wire-wound on a ferrite bean (as choke)
Potentiometer VR1 is acclimated to alter the axiological abundance admitting potentiometer VR2 is acclimated as ability control. For hum-free operation, accomplish the transmitter on a 12V rechargeable array backpack of 10 x 1.2-volt Ni-Cd cells. Transistor T2 charge be army on a calefaction sink. Do not about-face on the transmitter after a analogous antenna. Adjust both trimmers (VC1 and VC2) for best manual power. Adjust potentiometer VR1 to set the axiological abundance abreast 100 MHz.
This transmitter should alone be acclimated for educational purposes. Regular manual application such a transmitter after a licence is actionable in India
