Ham Radio 101 — The RF Engineering Behind the Signals

HF Foundations (Physics without the pain)

1. It all starts with Lambda ... [NL] [FR]
2. dB You’ll Actually Use (power, voltage, field strength; S-units ≈ dB)
3. Maxwell’s Equations—Lite, for Antennas (intuitive field picture)
4. Waves on Lines (reflection, VSWR, return loss, Poynting vector)
5. R, X, Q & Resonance—Why SWR Isn’t the Whole Story
6. Skin & Proximity Effects (HF conductors, ground return physics)
7. Noise on HF (atmospheric, galactic, man-made) and why NF rarely dominates on HF
8. Why I²R Matters (loss budgets from PA to far-field)

Antennas (How current becomes radiation)

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. Current in Motion – The Secret Behind Radiation [NL] [FR]
2. Where the Current Flows, the Signal Grows (current distribution & hot spots) [NL] [FR]
3. Understanding Polarisation – Why It Matters for Your Antennas (linear vs slant; cross-pol loss in practice)
4. Impedance and Matching (what the radio “sees”; translators: tuners, baluns, ununs)
5. Resonance – Why Resonance Isn’t Always the SWR Sweet Spot
6. DC Grounded vs Open Antennas
7. Radiation Patterns (Elevation & Azimuth) — takeoff angle intuition
8. Ground Systems & Radials (verticals, return currents, real-earth models)
9. Understanding Antenna Gain and Pattern
10. Matching Networks and Efficiency: Where Power Gets Lost
11. Multiband Strategies — traps vs fans vs OCF vs EFHW; efficiency & pattern tradeoffs
12. Height, Ground, and the Near Field — environment-driven pattern shifts
13. Mechanical & Weathering — wire, strain relief, ice/wind, corrosion

Baluns, Ununs, Chokes & Isolation

1. Common-Mode & Return Currents on Coax (the hidden second antenna)
2. Chokes vs Line Isolators — what each cures (and doesn’t)
3. Choke Cookbook — ferrite mixes (31/43/52), turns, target Zcm, placement
4. Baluns (Current vs Voltage) & Ununs — core choice, power/saturation, winding topologies
5. Measuring Success — clamp-on RF ammeters, VNA fixtures

Feedlines & Station Entry

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. Coax as a System — loss, velocity factor, power limits, thermal issues
3. Currents on the Coaxial Cable – A Multi-Lane Highway of RF Behavior [NL]
4. Feedline Loss & Velocity Factor
5. Mismatch on Purpose — stubs as band-stop filters
6. Bulkhead, Arrestors & Single-Point Bonding
7. Connectors & Weatherproofing

Propagation You Can Use (HF only)

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. Grayline & Day/Night Windows
3. HF Bands at a Glance
4. NVIS vs DX Angles
5. Seasonal/Latitude Effects & Noise Floors
6. Path Engineering Lite — how to read VOACAP/Proppy outcomes (no ops; physics of angles)

Transmitters & Power Amplifiers

Where DC meets RF. Transmitters turn energy into signal, and power amplifiers decide how cleanly you deliver it to the antenna.

1. Spectral Purity — IMD, splatter, harmonics; why linearity costs efficiency
2. PA Classes & Linearity — AB/B/C vs E/F; device limits, biasing & heat
3. Low-Pass, Band-Pass & Notch Filtering — keep it in-band and within limits
4. Directional Couplers & Samples — measuring forward/reflected power properly

Clean signal = respected neighbor. Understanding spectral purity and filtering keeps your station compliant and your signal pleasant to hear.

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
2. Noise Basics: S-meter, SNR, and Local Noise Mapping
3. Loops & Magnetic Receive Antennas (K9AY, small loops)
4. Phased & Parasitic RX Arrays
5. Choking & Isolation for RX Systems

Antenna System & Measurement Basics

1. Why I²R Matters
2. Why Resonance Isn’t Always the SWR Sweet Spot
3. Grounding & Lightning Basics
4. Station Layout & RFI in the Shack
5. Measuring SWR, R & X
6. Smith Chart—Lite Edition

Good to Know

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