Portable VHF-FM radio microphone
In the Radio Amateur magazine published a description and diagram of the portable FM wireless microphones. In my opinion, it has a large size, and the supply voltage it is also too large. In addition, the range of this device that uses radio range should be 250 meters (which is not bad for an Amateur design is obviously too much), five or six times less. Then there will be a sufficient guarantee that this device will not prevent listeners УLW-band.
Offer design FM wireless microphones on the same frequency. The device has a minimum weight and dimensions. If desired, it can even be attached to the lapel of his jacket. Makes this minibardaki and low current consumption. which is also important for maintaining stability of the frequency due to a sharp reduction in the supply voltage. The range of the wireless microphones - 40 meters. "Care" of the oscillator frequency is relatively small, and at room temperature is almost imperceptible.
Scheme of wireless microphones (figure 1) includes only two transistors. First, VT1, is used as an amplifier small selectednode microphone. The modulating signal is fed through the coils LI, L2 of the variable capacitor and the transistor VT2. in the purpose of a header which contains the loop L3. C4 is tuned to the frequency of the radiation. The capacitor C5 achieve an acceptable level of frequency deviation. The antenna is cut short, 20-30 cm, soft, stranded wire.
Coils L1 and L2 wound on the ferrite size KB in size and contains 30 turns of wire sew-0,2. Coil L3 frameless, has 5-7 turns of silver coated wire 0.5 mm, wound on a mandrel with a diameter of 7 mm. Nearby are two turns of the coil connection L4 to the same wire. Power wireless microphones composed of two small disk batteries type D-0,06. The establishment of the transmitter is to rebuild the capacitors C4 and C5 to capture the signal УSW FM receiver. The housing and the arrangement of the elements can be very different. Only need to adhere to the known requirements of the installation УSW equipment.
I. SHCHERBAKOV, Alma-ATA