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Why did the cable industry choose 75-ohm coaxial cable — and not 50 ohms? The answer is rooted in physics, engineering tradeoffs, and decisions made decades ago that still define every HFC network running DOCSIS today.

Brady Volpe and Ron Hranac break down one of the most fundamental design choices in cable network history: why 75-ohm characteristic impedance became the standard for outside plant, Why did the cable industry choose 75-ohm coaxial cable — and not 50 ohms? The answer is rooted in physics, engineering tradeoffs, and decisions made decades ago that still define every HFC network running DOCSIS today.

Brady Volpe and Ron Hranac break down one of the most fundamental design choices in cable network history: why 75-ohm characteristic impedance became the standard for outside plant, subscriber drops, and everything in between.

What you’ll learn:

  • What characteristic impedance actually means — and why it matters
  • The coax geometry behind minimum signal attenuation (~77 ohms)
  • Why 50-ohm cable dominates RF test equipment and wireless infrastructure
  • The power-handling vs. signal-loss tradeoff that drove the industry to 75 ohms
  • How this decision still shapes DOCSIS, HFC, and broadband network design today

Whether you’re a field technician, plant engineer, or broadband professional — this is the engineering history you were never formally taught.

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About Ron Hranac

Ron Hranac is a 50-year veteran of the cable industry with experience spanning both operators and vendors. An SCTE Fellow and co-founder of the Rocky Mountain Chapter, Ron was inducted into the SCTE Hall of Fame in 2010.

Honors include: SCTE Chairman’s Award, SCTE Member of the Year, Excellence in Standards Award (Cable-Tec Expo 2016), European Society for Broadband Professionals’ Tom Hall Award (2016), and the David Hall Award for Best Presentation (2017).

Ron has published hundreds of technical articles and papers and spoken at cable industry conferences worldwide.

00:00 Why Did Cable Pick 75 Ohms?
00:09 Intro
01:22 Why 75 Ohms Matters
03:44 What Characteristic Impedance Means
06:22 Can You Measure Coax Impedance?
08:10 Skin Effect and Real-World Coax
12:54 The Transmission Line Model Explained
19:12 What Sets Cable Impedance?
23:13 Why Kinks Cause Reflections
25:34 Dielectric Constant Explained
26:01 Vacuum vs Foam Dielectric
29:26 How Water Changes Cable Impedance
33:15 Water in Drop Cable: Full-Band Capture Example
37:47 Characteristic vs Electrical Impedance
39:57 Why the Cable Industry Uses 75 Ohms
41:04 Military Surplus Coax and Early CATV
45:30 Bell Labs and the 77-Ohm Loss Curve
51:05 Myths About 75 Ohms
58:02 The Real Answer
01:01:16 Why Terminators Matter
01:02:18 Return Loss and Impedance Mismatch
01:05:44 50 Ohms vs 75 Ohms in TV Systems
01:07:06 Is HFC Obsolete?
01:12:49 Outro

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