Small Radio Transmitters

Posted on Feb 4, 2014

Information about building a small radio transmitter, which has a PCB 1. 75` x 2. 5` (45mm x 68 mm) and has a range of about 30 yards or so. The documentation with the circuit says the freq range is 100-108 MHz, but I have found it to be more like 85-100 MHz. The circuit is (of course) only mono, and accepts an audio input from either a mic

Small Radio Transmitters
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rophone or other source. The input impedance is 1Mohm. The input sensitivity is 5mV and the max input signal is 10mV. The transmitted signal can be picked up on a FM radio. The circuit can be used for short-range transmission, eg. for wireless microphones. The actual circuit comes from a `Kit`, available from Veleman electronics (USA distributor is Tapto Corp. , PO Box 1339, CLAREMONT NH-03743-US. UK distributor is High-Q Electronics, 382 Edgware Road, London, W2 1EB). The kit number is K1771. It is a very good transmitter. I bought the kit, and made the circuit, which worked very well. I wanted two transmitters, so I made my own `copy` PCB and built the circuit, and in fact my home-made version seems to work better than the original! So there is no need to buy the kit really, as it is quite a simple circuit, and is the best `home-made` transmitter I have seen. PCBPLAN. GIF shows the PCB layout from above (components shown). PCBPLAN. GIF is an accurate layout, scanned from the instruction sheet. I have used * to mark one corner for reference. TRACKS. GIF shows the track layout on the soldering side of the board. This is NOT a very accurate layout. This is because I didn`t actually have a plan of the track layout. To get TRACKS. GIF, I put a bit of OHP film onto the bottom of the PCB, and traced the tracks with an OHP pen. I then scanned this in. I have marked the component leg holes (approximately) with white blobs. Then...

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