AM RADIO

INSTRUCTION SHEET

Price - Stock No 170

Check your kit 

Schematic Diagram

PCB Layout

Viewed from the component side

The MK 484

THE BC 337

Check Your Kit

• Components

1. Make  a  visual check of the P.C.Board to ensure no damage has happened in transit.  Continuity of the tracks can be  checked  with  a  multimeter  or an electronic Circuit Tester.  Any breaks can be bridged with solder.
2. Identify the resistors either by their colour bands, or with a multimeter.  Bend the legs to match their holes and assemble them.   It is a good idea to solder progressively as 4 or 5 components are mounted to the board.  
3. The 5K trimpot will fit the three holes in the board. Push the legs right down.
4. There are two 0.1uF and one 0.01uF capacitors.  Mount the capacitors in their correct positions and solder in place.
5. Nine pins are in the kit.  These are soldered into the four inductor connection points, one antenna point, two for the battery points and two for the jack socket. 
6. Insert the tuning capacitor and solder.
7. The  BC 337 and the MK 484 must be insert in the correct orientation.  The component and PCB diagrams above will assist.  Caution should be exercised when soldering these components.  Excess heat may damage these components however, sufficient heat from your soldering iron should be applied to make sound connections.
8. Solder the jack socket to it's PCB pins.
9. Connect the battery holder - Black to 0 V, Red to + 1.5 V.
10. Connect the antenna (hook up wire).
11. Connect the four leads of the inductor.  These are colour coded and caution should be taken to identify and correctly connect them.
12. Your AM radio is now complete and ready for a battery and testing.

Circuit description and tuning notes

The heart of this circuit is the MK 484.  It is a purpose built AM radio.  The radio station is tuned with the variable capacitor, which in conjunction with the inductor isolates a frequency on the AM radio spectrum.  The information (talking / music) on this frequency is delivered to the MK 484 at it's input - leg 2.  The output, which is quite low level is then coupled (via a capacitor) to the base of the BC 337.  The BC 337 amplifies the information to a level that can be heard through an earpiece.

The output of the MK 484 will vary according to the signal strength of a particular radio station.  A radio station transmitting from an antenna in your locality will generally have a higher strength than one 100 km away.  To allow for this, provision is made to change the sensitivity of the MK 484 through the 5 K trimpot.  (You can make an analogy to a volume control).  On a high strength radio station, you may need to adjust the trimpot to eliminate any distortion (the signal is too strong).  On a low strength radio station, you may need to adjust in the opposite direction to increase sensitivity (volume) to an acceptable level. 

TROUBLESHOOTING

If the AM Radio doesn't work check the following:

• The trimpot is in a central location - ready to be adjusted when the desired radio station is found.
• The BC 337 ank MK 484 are inserted correctly.  
• The four resistor values are as the diagram shows.
• The inductor and battery wires are connected correctly.  
• Check  all  soldering.  Re-solder  any joints that look suspicious, making sure that the solder takes to the track as well as to the legs.

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