In urban terrain and in the presence of various shielding objects such as concrete walls, metal structures, etc., difficult to get the maximum range and efficiency of use of radio microphones, in the current direction of the development of machinery there is an increasing use of transmitters at higher frequencies.
So for example, if the same power at a frequency of 430-470 MHz radio waves to enter through these obstacles several times better than on the frequency of "civilian" range, but to use such devices, for playback requires a remand or receivers domestic purposes, supplemented with appropriate converters.
One of the best simple and effective designs wireless microphones shown in the figure. The signal from the microphone VM through the amplifier 3H VT1 passes to the input of the RF generator, made by the scheme of capacitive treatacne. The output circuit of the generator L1C5 tuned to the frequency of 235 MHz. Further, the output RF signal is amplified by a cascade transistor VT3, the circuit L2,C10,C11, which is tuned to the frequency of 470 MHz, which can change the capacitor C10.
The repetition scheme, the findings of the details you need to make as short as possible, the coils L1 and L2 positioned on the circuit Board perpendicular to each other. All stages must be screened from each other by the copper walls.
Coil L1 consists of 4 turns of wire PEL - 0.68 mm, wound on a mandrel with a diameter of 3 mm. the length of the winding L2 is 4 mm. contains 2 turns of silver coated wire with a diameter of 0.8 mm, wound on a mandrel with a diameter of 3 mm. Antenna - a piece of stranded wire with a length of 150 mm.
The current consumption of the RM is 12...15 mA, with a range of up to 300...500 meters.