This is a DIY kit, you need to solder the components. This is an ideal project for the intermediate RSGB examination, or school project. A "Harvesting" circuit converts radio waves into DC to charge a rechargeable 1.5 volt battery or super capacitor. ( The battery is not supplied with the kit). You will also need to supply a pair of standard 3.5mm headphones (Not a crystal earpiece).
Frequency using the on board capacitor covers popular UK AM broadcasts. Extended frequency coverage can be achieved by connecting an external tuning capacitor.
The charging circuit can be tested by transmitting on a nearby handheld transmitter.
Full assembly instructions provided.
Price includes UK postage
Schools and Clubs if you want a particular number then I can list in multiples.
Circuit description Incoming RF signals are converted into DC and used to charge an external rechargable battery connected to the battery terminals.( use crocodile clips provided) Alternative an electolytic super capacitor could be used. The RF to DC circuit can be tested by moving the TEST/CHARGE switch to the test position and transmitting on a handheld radio nearby.The switch should normally be left in the charge position.
The radio is a TRF single tansistor 2 band radio covering some of the popular UK AM radio broardcasts.The transistor is a “Darlington” transistor and is two transistors in one package. The transistor is doing the detecting and amplification, note their is no detecting diode. For further Longwave coverage down to 500KHZ an external tuning capacitor can be connected to the external tune terminals, in the order of 140pF or greater. Alternativly you can for HF operation connect an external Inductor across the external tune connectors. There is no stop on the tuning capacitor and will rotate continuously from min to max and back to minimum.
The intermediate exam level requires the measurment of voltage and current.The battery voltage can be measured across the V terminals and the current link can be removed to measure the current in series on the mAmp range.
An external aerial can be connected via the BNC connector this is isolated from the radio aerial and used only to harvest radio waves for power. In most cases only an earth connection is require for the radio to funtion. If stronge signals are breaking through and selectivity is poor then remove the earth and connect an aerial to the Radio aerial pad, use the cocodile clip provided.
The harvester circuit is a germanium bridge rectifer with input and output filters.The radio works with modern low impedance general purpose earphones,power is not used if the earphones are disconnected and the radio is left switched on.
With normal background radio waves and low powered transmitters (5 watts and below)the battery cannot be over charged.The ideal working voltage for the radio is between 1and 1.5 volts.A 2.2v Zenner diode D5 ensures that overcharging does not take place.
The radio can be tested by applying 1.5 vots with a charged battery across the battery terminals.