Radio in general is a technologically advanced field, and those who have obtained their ham radio licenses can tell you that learning some of that technology can be challenging. We've collected some links that can help you understand both the basics behind radio and some of the in-depth engineering that goes into the physics of radio, along with ways to improve your setup.

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History is a sub-topic of another page
Outdated educational is a sub-topic of another page
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Quick Links

Just starting out Antennas [general, VHF-UHF, HF] Grounding and bonding Propagation Noise Technology Digital Good to know Tips Chokes, filters, baluns Solar Specialized Other glossaries Other

Some technical and basic FYI related to ham radio

Just starting out

Beginner's Guide to Ham Radio (TechWholesale)
New ham tips (SB-ARC)
New ham podcast (ARRL)
Ham Radio for Beginners (Massachusetts Community Colleges)
A telecommunications timeline (brief, non-amateur history)
DX Code of Conduct

Antennas

General

Antenna basics
Understanding antenna resonance (by Noji)
Antenna gain (by Noji)
How antennas radiate (PDF)
Antennas and radiation patterns, Part 1
Antennas and radiation patterns, Part 2
What is angle of radiation?
Vertical vs. Dipole Angle of Radiation (important to understand)
Why (some) antennas look the way they do (IW5EDI)
Antenna education (W8JI)
Antenna theory (K9ERG)
More than you ever wanted to know about antennas [PDF]
Understanding Zepp and other end-fed antennas (W8JI)
Understanding Antennas for the Non-technical Ham (N4JA)
How Yagi beams work (non-technical, no-theory)
There's no free lunch (ARRL - radial-less verticals, miniature HF antennas, wild gain claims, etc.)
Open-wire Feed Lines (QST PDF)

VHF / UHF

How ground plane antennas work
Why 5/8-wave is near-optimal
Why a 5/8-wave vertical must have a counterpoise [toward the end of the page](W8JI)
How J-pole antennas work (Wiki)
Why J-pole antennas fed by coax must have a choke balun [feedline radiation](Wiki)
More on J-pole antennas
Even more on J-pole antennas (IW5EDI)
Technical analysis of J-pole antenna performance (W8JI)
How high to mount a ground plane antenna (higher than 1.5 wavelengths)
Thoughts on 5/8-wave antenna construction (ON6MU)
How close to mount two VHF antennas (10 dB/ft vertical proximity, 1 dB/ft horizontal proximity)
Video on 2 meter light bulb dipole [YouTube]

HF

Effect of radials on HF vertical antennas (good article — the Hustler 5-BTV and 6-BTV in particular)
Followed these guidelines to install my Hustler 5-BTV
The purpose of radials
Amplifiers vs. antennas for better HF
If you're not being heard, chances are you need a better antenna or location, not an amplifier
Antenna tuner basics (1994 ARRL PDF)
How a tuner "tunes" (excellent General-level article, including the math, by Davide Achilli IZ2UUF)
Your first HF dipole antenna
How high to mount a dipole antenna (around 0.4 wavelengths for local, higher than 1.0 wavelengths for DX)
Another article about dipole antenna height (between 0.15 and 0.20 wavelengths presents a 50 Ω impedance)
Traps (W8JI — very good and in-depth)
Random wire antennas (and more)
The isotron antenna (and an analysis [PDF])
The doublet antenna (all HF bands, requires a tuner) (another and yet another)
Rhombic antennas (W8JI)

Grounding and bonding

Understanding shack grounding and bonding in your house (see also station grounds and ground systems) (W8JI)
Grounding myths, facts, and solutions (excellent article — must read)
ARRL's common-sense take on grounding
RF Grounding [YouTube]

Propagation

Skywave propagation (by Noji) Skywave propagation nuts and bolts including ionization and recombination (Brittanica) How far can two-way radios communicate? Understanding solar indices (ARRL - excellent article) Quick Guide to HF Propagation Using Solar Indices (what it all means) How the Sunspot Cycle affects radio propagation (by Noji) How weather affects radio propagation (it can affect the conditions, but no set answer fits all) Essentially, rain , snow, and fog typically affect frequencies over 2 GHz very heavily, while affecting frequencies under 30 MHz very little On the other hand, lightning is the single largest contributor to atmospheric noise Furthermore, temperature inversions can result in tropospheric ducting, which typically affect frequencies greater than 90 MHz Understanding 10-meter Sporadic E (excellent article)

How to decipher this banner

Noise

Understanding noise, noise sources, and how to eliminate or reduce noise (by Noji)
Phase noise (excellent article)
Common-mode noise (W8JI)
Understanding noise and power line noise (technical, by W8JI)

Technology

Basics of AM and FM (by Noji)
How transistors work (by Noji)
SWR basics (PDF)
Why 50 Ω ? (arithmetic mean compromise between lowest loss and power handling for air dielectric)
Why 50 Ω ? (compromise between voltage tolerance and power handling for telephone cable)
Understanding ALC (Rob's web - PA3CJD)
Understanding Superheterodyne radio receivers (for the lay person)
Superheterodyne radio receivers (excellent book excerpt)

Digital

Digital radio waves (by Noji)
Getting started with digital modes [YouTube]
Fundamentals of direct sampling (by Panoradio)
Comparing D-STAR, DMR, and System Fusion (by Mike Myers, K3DO)

Good to know

Repeaters and how to use them
Radio football (Understanding the Fresnel Zone by Noji)
The magic of 6 meters
Measuring quarter-wave and half-wave coax stubs (with velocity factor calculation)
Understanding transmission lines for amateurs (W8JI, excellent)
Wind load explained (rough but good)
Thoughts from ARRL on Anderson Powerpole™ connectors [PDF]
Install Anderson™ Powerpole connectors on YouTube™ (9:40)

Tips

How to quiet a noisy receiver by AB4OJ
Mic gain and compression tips by W6LG on YouTube™ (14:53)
RF feedback and its prevention (Elecraft, Nov 1999)
RF feedback discussion (ARRL - good Q&A article)

Chokes, filters, baluns

Baluns 101 (by Noji)
Understanding baluns (excellent article) see also The Ugly Balun (good article, but poorly written)
Baluns: What They Do and How They Do It (ARRL) [PDF]
All About Baluns: Ask Dave #73 (Dave Casler) [YouTube 25:47]

Solar

Monocrystalline vs. Polycrystalline which is better? Mono is, but more expensive.

Specialized

Understanding IMD (excellent article)
Understanding ERP (effective radiated power) [more] (KB6NU)
Understanding radiation resistance (W8JI)
Radiation resistance vs. ohmic (loss) resistance (short but good article)
Radiation resistance (very technical article)
Understanding CW bandwidth (W8JI)
Understanding voltage (excellently written lay article)
Understanding image response by KA7OEI (indepth and very well-written)
Voting repeater systems (excellent article)
Understanding desensitization (technical article from a smartphone perspective)
Background behind CTCSS, DTMF, and PL tones (in-depth, somewhat historical)
ALC adjustment procedure by Alan Applegate KØBG (well-documented)
How we mis-use ALC by Leif Asbrink SM5BSZ (technical, well-documented)

Other glossaries

Amateur Radio Dictionary Wiki
ARRL glossary
AC6V glossary
QRZ glossary
Yet another glossary (radio wave and solar)

Joe Hallas articles in QST

Former ARRL technical editor (W1ZR), in his columns Getting to Know Your Radio

Receiver Gain Control (June 2006, p. 59-60) [PDF]
Fighting Interference and Noise with Filters (Oct 2006, p. 65) [PDF]

Other

OCF HF antennas The Windom antenna (W8JI) The G5RV antenna (W8JI) The G5RV antenna (and more details) (WØBTU) Split operations APRS SolarHam HamSCI (amateur radio for university students) One man's thoughts on the future of amateur radio (a bit bleak) RF Wireless World (good, educational material that's not strictly amateur) Do not use Belden 9913 for repeater (email from John Lloyd to Richard Bateman, 12-04-2017)

General atmospheric opacity chart