model aircraft monitor

1111.4.4041111 Older, i.e., not using a computer, radio controlled model aircraft are highly vulnerable to breaks in radio com- munication, which can lead-to a crash or the model landing out of reach, or both. Owing to the allocated radio fre- quency range being usurped by pirates, its is essential for every model flyer to make sure that the channel to be used is free. Even if it is, it is advisable to continue monitoring it. In combination with a short-wave receiver, the circuit presented here enables monitoring the 27 MHz radio control band. The aerial signal is filtered (26...41 MHz) and applied to the input of differential amplifier T1-T2. Since the current source of this stage consists Of an oscillator, the amplifier functions as a mixer. The crystal oscillator can operate with almost any crystal between 2 and 32 MHz. The output circuit, L4-05-C6, is tuned to about 27.2 MHz. This fre- quency is inversely proportional to the values of the coil and capacitors. The values of the...