Lab 9AM Transistor Radio

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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

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

Transistor Radio (Part A)

Crystalearpiece

A transistor amplifier circuit to drive a high impedance load

A small base current is amplified in to a large collector current

DarlingtonTransistor

A transistor amplifier circuit to drive a low impedance load

ResistorBox

Earbudsor Speaker

(Part B)

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.

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 eitherTurn off the base-emitter pn junction,Saturate the collector-emitter current,

Resulting in “clipping” and distortion of the signal

input

output

input

output

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 (upperscreen) to 0.2 Amps

In part B, keep the resistor box at 30 and above tolimit 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 areapplying a positive DC voltage to the base

http://en.wikipedia.org/wiki/Crystal_radio

Crystal Radio Resources