1. Lab 9 AM Transistor Radio Spreadsheet Upload Today Full Lab Report Due 2 PM Same Day Next Week Next week: Final Exam Practice. and, for 0301 (Thurs): Oral Presentations In two weeks (6, 7 May): in class Final Exam

2. Piezoelectric crystal earpiece >1 M  resistor in parallel with a 25 nF capacitor Earbuds ~10  resistor Your speaker ~10  resistor in series with ~ 0.2 mH inductor Load Impedances High Low

3. Transistor Radio (Part A) Crystal earpiece A transistor amplifier circuit to drive a high impedance load A small base current is amplified in to a large collector current

4. Darlington Transistor A transistor amplifier circuit to drive a low impedance load Resistor Box Earbuds or Speaker (Part B)

5. Transistor Radio With Earbuds (Part C) Trick: Start with the radio tuned to a strong signal. Then slowly increase the voltage of the DC power supply from zero and listen carefully for the signal in the earbud.

6. Some Issues with Transistor Amplifiers The base input requires a minimum DC bias to ‘turn on’ the base-emitter pn junction A large voltage swing on the base can either Turn off the base-emitter pn junction, Saturate the collector-emitter current, Resulting in “clipping” and distortion of the signal input output input output

7. Hints To start: One partner re-builds the radio circuit (lab 7) while the other builds the amplifier Limit the current from the DC power supply (upper screen) to 0.2 Amps In part B, keep the resistor box at 30  and above to limit the current going through the transistor. Don’t accidentally set it to 0  ! I suggest using only inexpensive earbuds in this experiment In part B, step 2, measure and make sure that you are applying a positive DC voltage to the base

8. http://en.wikipedia.org/wiki/Crystal_radio Crystal Radio Resources