50 Ohm Impedance Matching – Mystical, Magic, or Codswollup?

50 Ohm Impedance Matching –  is it something Mystical, the Magic solution to all feedline woes, or simply a bunch of Codswollup?

Perhaps it is a bit of all of these!

The average Radio Amateur’s gear is all nominally rated to use 50 Ohm coax feedline, matched to a 50 ohm feed point on an antenna.

What is meant by 50 Ohm?  

First it is NOT about resistance at all, but rather 50 Ohm IMPEDANCE.

What is this beast “Impedance” and how is it different than “Resistance.”

We have pretty good analogies for Resistance, how it is descriptive of how a material slows down the flow of current. Sort of like the lightbulb in our flashlights resisting the flow of the battery current to the point the wire itself glows with light!

“Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent.”

Lets consult some well written resources:

Emrcorp techinfo on Impedance – see the link “The Fifty Ohm Enigma” PDF download

Cable Impedance at Epanorama

http://www.physlink.com/education/AskExperts/ae517.cfm

http://wiki.answers.com/Q/What_is_the_difference_between_electrical_resistance_and_impedance

A study of these, and ARRL Radio Amateur Handbook information, shows that 50 Ohm Impedance Matching is a touch more complex than it would seem at first, with various situations being important and in others not an issue.

I’ve seen field day exercises where apparent mismatches were “leveled out” using military style improvised techniques and I have seen the improvement in signal both received and transmitted from careful matching.

Hope these resources cast some light on what at first seems an arcane subject area!

73

Steve

K9ZW

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One thought on “50 Ohm Impedance Matching – Mystical, Magic, or Codswollup?

  1. […] Co­ntinue h­er­e: 50 O­h­m I­mpe­d­an­­­c­e­ Mat­­c­h… […]

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