Signal School
Currents & Concepts

Lesson 5: Series & Parallel Circuits

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Introduction: Why This Is Foundational

Circuits aren’t just wires connecting parts. They’re paths that decide how electricity behaves, how power is divided, and how failure propagates. Understanding series and parallel circuits will help you:

  • Design or modify circuits confidently

  • Understand how antennas and tuners divide signals

  • Troubleshoot power systems and component failures

  • Grasp real RF systems like filter networks and antenna matching

Part 1: Series Circuits – A Single Path for Current

core principle:

In a series circuit, all components are wired one after another, like links in a chain. There is only one path for current to flow.

Characteristics:

  • Current is the same through every part of the circuit

  • Voltage divides across each component

  • Resistances add to form total resistance

Rtotal = R1 + R2 + R3 + ...

Vbattery = V1 + V2 + V3 + ...

Analogy:

Imagine a single garden hose with a few pinch points (resistors). The water pressure (voltage) drops a little at each pinch, but the same amount of water (current) flows through all of it.

Example:

You connect three 100-ohm resistors in series to a 12V battery.

  • Total Resistance = 300 ohms

  • Current = I = V/R =12V/300Ω = 0.04A

  • Voltage Drop per resistor = 4V

Failure Behavior:

If any component opens (like a burnt resistor or blown fuse), everything stops — the whole circuit is broken.

Part 2: Parallel Circuits – Multiple Independent Paths

core principle:

In a parallel circuit, components are connected so that each one gets its own direct path to the power source.

Characteristics:

  • Voltage is the same across each branch

  • Current divides among branches

  • Total resistance decreases

(1/Rtotal) = (1/R1) + (1/R2) + ...

Itotal = I1 + I2 + I3 + ...

Analogy:

Think of multiple hoses connected to a single faucet. Each hose receives the same pressure (voltage), but water (current) divides depending on how wide each hose is (resistance).

Example:

Three 100-ohm resistors in parallel with a 12V source.

  • Current per branch: 12V/100Ω = 0.12A

  • Total Current: 0.12A×3 = 0.36A

  • Total Resistance: ~33.3Ω

Failure Behavior:

If one branch fails open, others still work. This is why your house lights don’t all go out when one bulb dies.

Part 3: Mixed Series-Parallel Circuits

Most circuits in radios or power supplies are combinations of series and parallel elements. You can break them into parts and simplify:

  • First, calculate series or parallel groupings

  • Use Ohm’s Law to find current, voltage, or resistance

  • Continue simplifying step by step

This is essential for:

  • Voltage divider networks

  • Filter circuits

  • Power bus distribution

Real-World Ham Radio Applications

Application

Series or Parallel?

 Why It Matters
Power Distribution Bus Parallel One radio fails → others stay powered
Antenna Elements in Yagi Arrays Mixed

Control phase and direction of radiation lobes
SWR Meters Series

Sample current/voltage along feedline
Filter Networks Mixed

Combine capacitors and inductors to block or pass desired frequencies
Battery Banks (portable ops)  Both 

Series adds voltage, parallel adds capacity—choose based on gear requirements

Thought Experiment

Imagine two light bulbs: one wired in series, one in parallel.

You add a third identical bulb to the circuit. In which setup do all bulbs stay equally bright?

  • In parallel, each bulb still receives full voltage and stays bright.

  • In series, the voltage divides — all bulbs get dimmer.

This simple scenario helps visualize how load sharing changes based on layout.

Skills You Develop Here

  • Circuit analysis: Identify how electricity is behaving in a given design.

  • System optimization: Balance loads, avoid overcurrent, plan for failure.

  • RF system design: Understand signal distribution and impedance balancing in antenna arrays or tuner networks.

summary

Property

Series

Parallel
Path for current One shared path

Multiple independent paths
Voltage behavior Divides across components

Same for all branches
Current behavior Same through all components

Splits among paths
Resistance Increases (adds)

Decreases (inverse sum)
Failure mode All devices stop

Others keep working

Optional Visuals:

Would you like:

  • A circuit diagram set (labeled examples of each configuration)?

  • A real-world demo suggestion you can try with basic components?

  • An interactive link to simulate both kinds of circuits?