Analysis of Progressive Series Modulation Circuit with Six Transistors and Cascaded Diodes

How Does the Progressive Series Modulation Circuit with Six Transistors Work?

I am analyzing the progressive series modulation circuit

• Six transistors, Divided into distinct stages:

• Q1 and Q2 (TIP47): Modulator Stage

• Q3 and Q4 (2N6254): Operate in Parallel

• Q5 (2N6254): Connecting two Stages

• Q6 and Q7 (2N6340): Modulated Final Power Amplifier Stage

• Diodes:

• IN3070 and IN914(3): Connected after the audio input

• D1 (IN4005): Connect through DC volatage 71-volts

My Objectives:

1. Understand how the circuit works, particularly the roles of Q5, Q6, and Q7 in the final power amplifier stage.
2. Determine the Q-points for all transistors and their influence on the circuit operation.
3. Analyze the voltage gain, input impedance, and β (beta) for each transistor stage.
4. Explain the role of cascaded diodes (IN3070 and IN914) in the modulation process and their effect on voltage levels.
5. Calculate the voltage drop across each diode, including D1 (IN4005), and its impact on circuit performance.
6. Evaluate how Q6 and Q7 eliminate the need for a modulation transformer in this design.

Specific Cases to Explore:

1. Case 1: When Q1 (TIP47) turns ON at a specific voltage, how does it affect Q2 and the subsequent transistors (Q3–Q7)? How it will turn onn?
2. Case 2: When Q2 (TIP47) turns ON, what conditions lead to this? How do other transistors (Q1, Q3–Q7) respond, and how does it affect the modulation process?
3. Case 3: If Q3 and Q4 (2N6254) are ON, how does their parallel configuration handle higher power modulation, and what is their impact on Q5 and How the Q (3-4) will turn onn?
4. Case 4: If Q5 (2N6254) turns ON, what is its role in bridging the modulator and final RF stage? How does it affect Q6 and Q7 and How Q5 will turn on?
5. Case 5: When Q6 (2N6340) is ON, what conditions enable it to work with Q7 to amplify the modulated RF signal? and How it will turn onn?
6. Case 6: If Q7 (2N6340) is ON, how does it drive the RF output to the antenna, and what are the conditions for efficient operation? and How it will turn onn?

How Each Transistor Turns ON & OFF:

Goals:

• Investigate why transistors (Q5, Q6, and Q7) were chosen to eliminate the modulation transformer and how this impacts circuit design.
• Compare theoretical calculations (Q-points, gain, impedance, diode voltage drops) with practical measurements for validation.

For Text or Information from the Source:

The explanation of the progressive series modulation circuit with six transistors is adapted from Shoenbeck, Robert J. Electronics Communication Modulation and Transmission, 2nd ed., Archive.org, [https://archive.org/details/electroniccommun00robe]

Image Sources & Attribution:

• Circuit Image: Adapted from Shoenbeck, Robert J. Electronics Communication Modulation and Transmission, 2nd ed., Archive.org, https://archive.org/details/electroniccommun00robe, p. 49.
• Theory Image: Adapted from Shoenbeck, Robert J. Electronics Communication Modulation and Transmission, 2nd ed., Archive.org, https://archive.org/details/electroniccommun00robe, p. 48.