L1 is 0.112uH (this tunes to the middle of the FM band, 98 MHz, with VC1 at its centre value of 33pF). L1 is 5 turns of 22 swg enamelled copper wire close-wound on a 5mm (3/16") diameter former. Alternatively, you can have a fixed 33pF cap instead of VC1 and have L1 as an adjustable molded coil (eg UF64U from Maplin). VC1 will give you a tuning range of 85 - 125 MHz, and a possible choice is the Philips type polypropylene film trimmer (Maplin code WL72P). Two sets of oscillator bias resistors are given, the ones in the brackets give about 20% more RF power. Mike is our favourite Omnidirectional sub-mini electret (Maplin code FS43W). Ant is a (lambda / 4) whip monopole (eg 76 cms of 22 swg copper wire). Q1 is configured as a Clapp oscillator. Frequency modulation results from the audio voltage changing the transistor's base-emitter capacitance.
R7 3K9 (2K7)
R8 120R (82R)
All resistors except R8 are at least 0.25W rated. R8 is at least 0.5W rated
(the 0.6W metal film M-series from Maplin can be used for R1-R8).
author: Kamran Ahmed - UK