Ham Radio 101 — The RF Engineering Behind the Signals

Welcome to our beginner’s corner! This guide connects the dots between antennas, feedlines, propagation, and the quirks of RF behavior. It’s written in plain language—so you can get solid insights without needing an engineering degree.

Antennas

Antennas are how your radio actually touches the airwaves. Here we explore why length matters, how current creates radiation, and why “perfect SWR” isn’t the whole story.

  1. It all starts with Lambda ... [NL] [FR]
  2. Current in Motion – The Secret Behind Radiation
  3. Where the Current Flows, the Signal Grows
  4. Understanding Polarisation – Why It Matters for Your Antennas
  5. Impedance and Matching

Every antenna has an “electrical personality.” Impedance is how it resists or accepts RF current. Matching networks (tuners, baluns, ununs) act like translators, making your radio and antenna speak the same language.

  1. Resonance – Why Resonance Isn’t Always the SWR Sweet Spot
  2. DC Grounded vs Open Antennas
  3. Radiation Patterns (Elevation & Azimuth)

Antennas don’t spray RF equally in all directions—they form lobes and nulls. Think of it as a flashlight beam versus a bare bulb. Knowing the pattern tells you where your signal will actually go.

  1. Ground Systems & Radials (HF basics)

For vertical antennas especially, a good ground system makes the difference between a loud signal and a whisper. Radials don’t “soak up RF”—they give the return current a clean path back, completing the circuit.

10. Maxwell’s Equations

Feedlines

The wire between your shack and antenna isn’t just a cable—it shapes how signals travel, leak, and even reflect back. Ladder line and coax each tell a very different story.

  1. Ladder Line – The Almost-Utopian Feedline
  2. Currents on the Coaxial Cable – A Multi-Lane Highway of RF Behavior [NL]
  3. Feedline Loss & Velocity Factor

Feedlines eat some of your signal along the way. Loss increases with frequency and length. Velocity factor explains why signals travel slower in coax than in free space.

  1. Connectors & Weatherproofing

The humble connector can make or break a station. Learn why PL-259 vs N matters, how to crimp properly, and why waterproofing keeps the SWR gremlins away.

Common-Mode

When your coax starts acting like part of the antenna, strange things happen: noise creeps in, SWR shifts, and RF comes back into the shack. This is the hidden “second antenna” every ham needs to tame.

  1. Common-Mode and Return Currents on Coax
  2. Chokes vs Line Isolators

Chokes stop RF from riding back on the shield. Line isolators take it a step further by adding high rejection across a wider band. Knowing where to place them makes all the difference.

  1. Baluns & Ununs

Baluns balance currents, ununs match impedances. They’re the unsung workhorses that let strange antennas and feedlines play nicely with your radio.

Propagation

Even the best antenna can’t change the sky. The ionosphere bends, absorbs, or skips signals depending on solar conditions. Knowing the “radio weather” is as vital as knowing the bands.

  1. Radio Weather: K-Index, Solar Flux, and More
  2. HF Bands at a Glance

Each HF band has its own character. 160 m for night-time locals, 20 m for daytime DX, 10 m when the sun is awake. Think of them as different highways through the ionosphere.

  1. NVIS vs DX Angles

Near-vertical incidence skywave (NVIS) fills in the close range, while low DX angles hop signals across continents. Choosing antenna height decides which you’ll get.

Antenna System

An antenna system is more than a single wire: it’s the feedpoint, ground, losses, and all the little details that decide how much of your RF actually gets out—or back in.

  1. Why I²R Matters [NL]
  2. Why Resonance Isn’t Always the SWR Sweet Spot
  3. DC Grounded vs Open Antennas
  4. Grounding & Lightning Basics

There’s RF grounding and there’s safety grounding—they’re not the same. Learn how to bond gear, route lightning safely, and still keep your antennas efficient.

  1. Station Layout & RFI in the Shack

That mysterious hum in your speakers? Or your touch lamp that flickers when you key up? Good layout, bonding, and ferrites keep RFI from haunting your shack.

  1. Measuring SWR, R & X

Analyzers don’t just show “SWR”—they reveal resistance (R) and reactance (X). With a little practice, these numbers tell you exactly what’s wrong with an antenna.

  1. Smith Chart—Lite Edition

The Smith Chart looks scary—but all you really need is the basic picture: how impedance transforms on a feedline. A pocket map for taming mismatches.

Receive Antennas

Why does an antenna that’s great for transmitting sometimes fall short on receive? Here we peek into reciprocity—and why listening is its own science.

  1. Reciprocity in the Real World

Textbooks say transmit and receive are identical. Reality says otherwise. Noise, local RF pollution, and common-mode currents can make an antenna that shines on TX disappoint on RX.

  1. Noise Basics: S-meter, SNR, and Local Noise Mapping

The S-meter shows signal strength, but what matters more is the signal-to-noise ratio (SNR). Learning how to spot and tame noise sources is half of winning the RX game.

  1. Loops & Magnetic Receive Antennas (K9AY, small loops)

Small loops work not because they’re efficient radiators—but because they’re quiet listeners. They excel at rejecting local noise and can be turned to null interference.

  1. Phased & Parasitic RX Arrays

By combining multiple antennas with timing or switching, you can “steer” your listening beam and carve deep nulls into noise sources. This is how serious DXers dig weak signals out of the mud.

  1. Choking & Isolation for RX Systems

RX antennas often live close to noise. Strong choking and isolation on feedlines keep the unwanted household RF from overwhelming your weak DX signals.

Good to Know

A grab-bag of practical lessons: grounding for lightning, hidden inductive loads, and how to tell skin effect from common-mode in your shack.

  1. #1 Mistake Hams Make During Thunderstorms—Fix It Before It’s Too Late
  2. The Inductive Load: Why It’s the Convenient Radiator in RF Systems
  3. RF in the Shack: It’s Skin Effect, Not Common Mode
  4. RF Exposure & Safety

RF exposure limits aren’t about frying yourself—they’re about long-term safe levels. Learn the simple checks that keep you, your family, and neighbors safe.

  1. Operating Basics, Band Plans & Good Practice

From “listen before you talk” to knowing the digital watering holes, these basics keep you friendly on the bands and in tune with good amateur practice.