We are talking about miniature and low-power VHF transmitter that operates at a distance of only a few tens of meters. The contractor, using a wireless microphone, can move freely around the stage and even down the hall, not being tied to a long cable with amplifying equipment. Sent by the wireless microphone signals taking on a normal VHF radio range. Then, if necessary, enhance them with powerful uzch and reproduced through loudspeakers.
The scheme of this device was published in Bulgarian journal “Radio Electronics Tilesize”. It consists of a microphone amplifier (VT1), modulator (VT2) and a VHF FM transmitter (VT3). Antenna WA1 — cut insulated wire with a length of 30-50 cm Chokes L1, L2 comprise 30 turns of wire PEV 0,2, wound on a ferrite ring Ø 6 mm. Contour coil L3 — frameless, Ø 7 mm — consists of 5-7 turns of bare silver wire Ø 0,5 mm. At setting it compress or stretch. Coil connection L4 — 2 loop of the same wire.
Microphone ВМ1, battery type “Crown” and the circuit Board placed in a common plastic housing of cylindrical shape.