Powerful microtransmitter that can cover 3km range. To amplify the signal, a 2N3866A transistor is used that can provide up to 1W with gain > 10dB (24Volt). In our case the output power is about 100mW depending on the input power of 10mW and 9V battery power supply. The transistor Q1 must be mounted with a heatsink, the heatsink must have small dimensions (cylindrical) in order not to increase the parasitic capacitance. The trimmer R2 serves to adjust the bias of the transistor, start with the trimmer fully open and close by measuring the current absorbed by the 9V, in my case you get 100mW at the output with a current of 50mA not increase this value as you only increase the absorption by heating the transistor without increasing output power, because the input power is too low. Clearly the 9V battery will be able to provide 50mA only for a few hours, if necessary have greater autonomy should be used a larger battery, but it is no longer a bug but simply an FM transmitter.
Build Accurate LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and reset function to make sure the readings are as accurate as possible ... [more]