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Colpitts
oscillator. Its frequency depends on the capacitance of the vary
cap diode. The center frequency is changed by varying the biasing
voltage of the vary cap through the 47K pot. You can use a 75cm
telescopic antenna or simply a length of hook-up wire. Mine worked
fine with a 6cm hook-up wire and gave a range of 100m with a good
FM receiver. The approx. cost of the circuit is around Rs.35
Coil Details (Print on the
PCB itself)
The coil shown below can be
constructed on the PCB itself as PCB track. Just transfer the
dimensions on a copper board and etch it. If the 1mm spacing is
difficult use a sharp blade to remove unwanted copper.
You can also use a copper wire and construct a square spiral of
the dimensions shown below. Please note that a small deviation
from the given dimensions is permissible.
Note: You can even try a coil made of 18SWG copper wire of 5
turns and 5mm dia with air core. The center tap can then be taken
at the 2nd or 3rd turn.( I have'nt tried it tell me if it works
well)
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