#One transistor fm radio portable#

Sound waves hitting the microphone induce a voltage that varies in time with the sound and this voltage is applied via C1 to the base of Q1, thereby frequency modulating the transmitter.ĮSR Meter / Capacitance / Inductance / Transistor Tester KitĮSR Meter kit is an amazing multimeter that measures ESR values, capacitance (100pF - 20,000uF), inductance, resistance (0.1 Ohm - 20 MOhm), tests many different types of transistors such as NPN, PNP, FETs, MOSFETs, Thyristors, SCRs, Triacs and many types of diodes. This capacitance, which is known as the 'junction capacitance', is not fixed but varies when the voltage on the base of the transistor varies. In particular, the capacitance between the base and the collector of Ql has a small but noticeable effect on the oscillation frequency. Although CV1 accounts for the major part of this capacitance, other parts of the circuit also make minor contributions. Some of the energy in the oscillating electric and magnetic fields of the tuned circuit is radiated as radio waves.īut how do sound waves arriving at the microphone vary the frequency of these waves? They can do this because the frequency of the oscillations depends on the TOTAL capacitance in the oscillator circuit. This makes the base-emitter current of the transistor vary at the oscillation frequency and hence current flowing in the tuned circuit and maintaining the oscillations. The oscillating current would very soon decay to nothing, but for the fact that the oscillating voltage is fed back via C4 to the emitter of Q1. is fairly delicate so avoid unnecessary adjustment. The Variable Tuning Capacitor- in the Radio Mic.

#One transistor fm radio portable#

it you are tuning on a car radio, or a portable with a vertical antenna the transmitter will probably work better if the antenna is hung vertically, Generally the transmitter antenna works better if it is in roughly the same plane as the receiver antenna eq. Try hanging the antenna straight up or down. A longer wire doesn't autornaticaliv work better. Try a length of wire attached to the antenna to see if that improves the periormance remember that there is a premium lenath for the antenna.

Move the aerial around to get the strongest signal.Ģ. Tune the receiver rather than the transmitter. Tune the approximate frequency to a clear part, of tile dial around 100 Mhz and try transmitting. Generally the wire antenna supplied is fine but extending and/or shortening the length of the antenna could be tried if reception is poor.ġ. Premium transmission often requires the antenna to be moved around to suit the location of the Receiver and other conditions. E transmitter antenna is a short piece of insulated wire and connected to the PCB by soldering to a Circuit-board Pin at the antenna point on the PCB.