All ham radio equipment depends on stable, reliable electrical power. Most gear runs on DC (usually 12–13.8V), but wall outlets provide AC — at dangerous voltages. This section helps you understand:

How voltage is converted, stepped down, and regulated
Why transformers are essential for isolation and voltage change
What makes a power supply “clean” or “dirty”
How to choose or build a power supply for your shack

Transformers – Changing Voltage and Providing Isolation

What They Do:

Transformers use magnetic induction to step voltage up or down between two coils of wire wound around an iron core.

They:

Change AC voltages (e.g., from 120V down to 12V)
Isolate circuits electrically (no direct connection between input/output)
Work only with AC, not DC

Transformer Equation:

\frac{V_{p}}{V_{s}} = \frac{N_{p}}{N_{s}}

Where:

V_p = primary voltage
V_s = secondary voltage
N_p, N_s = number of turns on each winding

So: more turns = higher voltage, fewer turns = lower voltage

Types of Transformers in Ham Radio:

Type	Purpose
Power Transformer	Steps down AC for power supplies
Audio Transformer	Matches impedance between audio stages
Balun (Transformer)	Matches impedance from unbalanced to balanced antennas (e.g., coax to dipole)

Power Supplies – Turning Wall Power into Radio-Friendly DC

After a transformer lowers the voltage, a power supply converts that AC into smooth, reliable DC for your transceiver.

Parts of a Basic Linear Power Supply:

Transformer – Steps 120V AC down to ~16V AC
Rectifier – Converts AC to pulsating DC (using diodes)
Filter – Smooths out the ripples (using capacitors)
Regulator – Outputs clean, steady voltage (often 13.8V)

Linear vs. Switching Power Supplies

Feature	Linear	Switching (SMPS)
Size/Weight	Large and heavy	Compact and lightweight
Efficiency	Less efficient (more heat)	High efficiency
Noise (RF Interference)	Very low	Can be high (if unfiltered)
Cost	Often more expensive	Usually cheaper
Use Case	HF rigs, sensitive equipment	Portable ops, mobile, budget gear

For HF operations, be careful with switching supplies — some emit RF noise that can ruin your reception if not well-shielded.

Voltage Regulation – Keeping It Steady

Radio gear is sensitive — a 13.8V device might fail at 15V or shut down at 10V. A good power supply includes:

Linear regulators (like the 7812 chip): Clean but inefficient
Switching regulators: Efficient but can introduce noise
Crowbar circuits: Protection against overvoltage spikes

Some power supplies also have:

Current limiting
Over-temperature shutoff
Metered displays for voltage and amperage

Thought Experiment

Imagine your power supply like a kitchen faucet:

Transformer = adjusts water pressure
Rectifier = changes water from pulsing spray to steady flow
Filter = removes pulses and grit
Regulator = keeps pressure exactly right for the appliance

If pressure (voltage) is too low, your washing machine won’t run. If it’s too high, it breaks. Your radio is the same way.

Real-World Ham Radio Applications

Component	Type	Why It Matters
Base station power supply	Regulated DC	Must deliver stable voltage to transceivers
Battery + solar charger	DC + inverter/MPPT	Powers radios off-grid or in emergencies
Linear power amplifier	High-current DC	Requires beefy power supplies with 25–50 amps
Portable QRP rig	Battery-powered	Must avoid voltage sag during transmission
Balun or unun	Transformer-type	Impedance matching with magnetic isolation

Summary

Topic	Key Point
Transformers	Step AC voltage up or down, provide isolation
Power supplies	Convert AC to clean DC for radio use
Linear vs SMPS	Tradeoff between weight, cost, and RF noise
Regulation	Ensures safe, consistent power for sensitive gear

Optional Add-ons

Would you like:

A diagram of a full power supply circuit (transformer → regulator)?
A comparison chart of real-world power supply models?
A troubleshooting guide for when your gear isn’t getting power?

Lesson 9: Transformers & Power Suppleis