The circuit shown depicts a wide band FM wireless microphone. Its power and range are similar to the commonly known circuits, which use bipolar transistors. The simplicity of the design means it is certain to work first time. One gate circuit of the MOSFET is a self excited RF oscillator, and the other gate circuit acts to bias the device and also as a microphone pre-amp and modulator.

Tuning can be effected by making Ct a trimmer/padder capacitor, or alternatively if this is a fixed value, then expanding compressing the coil should give some variation in frequency. Almost any dual-gate N-Channel MOSFET should work; suitable types are 40673, 40822, BF900, BF988 . A 9V battery is used as a power supply

This project is a miniature VHF-FM (Broadband) Wireless Microphone transmitter of the type commonly referred to as BUG's. Note that the "bug" is illegal, but "Wide-Band Wireless Microphones frequency modulation (WBFMWMs) are not so many people have told me (including the RSGB). In addition, the sensitivity of the AF-Channel prevent bugs spreading gutters ! Personally, I would start with one of these WBFMWMs RF platform to my headphones, so I "earwig" QSO's and networks in sitting on the toilet, dishwasher coal, etc., I know from experience that this project can be used to stimulate ' Radio interest older children, and was also one of the projects for which a group of boy scouts and girl guides to build. Surprisingly, the girls have found a better job of sealing kids! The circuit is very simple and not require any explanation for the building, while children orientation of the weld.


The coil version uses a 1/4" (4mm) diameter coil wound on a drill bit, although the PCB version has the coil fabricated on the PCB itself. A simple piece of insulated wire about 60 cm (2 feet) was fine for the antenna, and is connected to a 1-turn tapping of the coil. Use tinned copper wire for the tuning coil and not the enameled wire for kids to build. It is much easier for them to solder the antenna, without "mashing-up" the coil, whilst trying to remove the enamel. The PCB version is ideal for the kits as there is no coil to wind, see the photographs on this page.

Note:
Since the antenna is right on the pulse of the track coil, the last frequency of the oscillator, when the antenna or the battery is affected. This may seem a small stable. This is a normal feature of this type of track. To avoid this, you must have a buffer of antenna / amplifier, but only for the complex - is not ideal for beginners. My FM Wireless microphone V5, if you have a stable.


If the bug (sorry!) FM wireless headphones with a microphone platform HF, and then remove the resistance of 4K7 (and vice versa 1uF capacitor). The circuit is a "electret" condenser microphone. The issuer must be received by May VHF-FM radio, the radio, but I was the bag house free Weetabix box until a few years ago. The device must have a minimum distance of 100 meters (250 feet), but the increase of 220 ohms of resistance against the issuer of 1 km to reduce (if you believe that too little Johnny planting in you and your wife a room bed). Here is a table to give a performance of the bugs (sorry! Order, as I said!) Microphone Wireless FM Transmitter:

Emitter Resistor	Supply current	Range (approx)
100R	30 mA	500metres
220R	11 mA	120metres
330R	8 mA	100metres
1K0	5 mA	50metres