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INTERMEDIATE LESSON 30

LEARNING OBJECTIVES -

Practical skills

This section summarises the practical skills that candidates for the examination have to demonstrate. Here are some brief notes just to remind you, but it is best to practice these before the examination.

10d.1 *Read the colour code bands on a number of different resistors and confirm their value by measurement.	Go back to the last lesson (lesson 29) to remind yourself how to read the value of a resistor from the colour code.
10d.2 *Demonstrate the ability to make good soldered joints.	Remember the order for soldering a joint is: Turn on the soldering iron and let it get to temperature Clean the tip on a wet sponge to remove oxide Tin the tip with some solder containing flux Apply the soldering iron to the joint to be soldered Apply the solder and when it has formed a covering of solder remove the iron Do not move the joint Inspect to check you haven't produced a dry joint.
10d.3 Construct a simple circuit containing a battery, resistor, LED, lamp and switch. 10d.4 Measure potential differences and currents in a simple circuit. 10d.5 *Demonstrate that a diode will only conduct in one direction in a simple DC circuit 1. Close the switch. Note what happens 2. Turn the diode round so that it is connected the other way round. Note what happens. Explain you observations 3. Measure the potential difference across these parts using a multimeter: the 9V battery when the switch is open the 9V battery when the switch is clods The 1k Ohm resistor when the switch is closed The lamp when the switch is closed The LED when the switch is closed Explain you observations 4. Measure the current at points: A B C D Explain your observations	The circuit should look like this:
10d.6 *Demonstrate that a transistor can be used as a switch in a simple DC circuit. In this circuit a small current can be used to switch on something taking a larger current. Here the application of 5V to the base will cause a small current to pass from base to emitter. This will cause a larger current to flow from collector to emitter. This could be used to switch on a relay in the collector circuit. The relay switch could then be used to switch on an even higher current. A low power device could be activated with just the current flowing from the +12V line to the collector.
10d.7 *Fit a suitable RF connector (PL259, BNC or N-type) to a piece of coaxial cable. To fit a PL259 to coax Select a PL259 plug that has a coupling ring to match the size of coax you are using. Cut the coax to the required length. Unscrew the coupling ring from the plug and put it onto the coax with the threaded end nearest to the cut end of the cable. Remove 30mm of the black plastic on the outside of the coax with a sharp knife, but avoid cutting the braid Apply molten solder to the braid Cut off the soldered braid , at 11mm from the end of the braid. Remove the dialectric from the tip for 9mm. Roughen the edge of the hole in the PL259 with a file so that it takes solder Srew the plug onto the coax making sure the central core fits into the hole in the plug. Solder the central wire to the plug and cut off any protruding wire. Solder the braid through the hole. You will need a high wattage soldering iron. Screw the coupling ring to the plug Check with a multimeter that the inner and braid are not shorted together. Check the centre pin is connected to the coax centre.	This video shows you different mothods for fitting a PL259 plug to coax: http://www.youtube.com/watch?v=8ecfu7s8rPw
10d.8 Fit a 13A plug to a piece of three-core mains cable.	See Foundation Lesson 15 for instructions on wiring a plug.
Construction 10e.1 * Construct a simple amateur radio related project (e.g. direct conversion receiver, crystal calibrator, ‘grid’ dip meter, ATU and SWR meter, Morse oscillator, audio amplifier) either from a pre-prepared kit or from a published or personal design. Construction may be carried out either within a course or elsewhere, but the assessor must be satisfied that the bulk of the work is that of the candidate.	There are a lot of simple kits on the market that will include a printed circuit board, components and often a suitable box. An alternative is to buy the components separately and mount them onto either veroboard or a plain piece of copper clad board. Try to make something that you will find useful in the shack.