End Fed, Dipole, Off Center Fed Antennas: Which is better? Jim W6LG Shows a Brief Animation

Comments · 115

• JE

  @Jerrythenerdful · 2 years ago (edited)

  It is incorrect or misleading to say an end fed does not need a counterpoise. It always needs a counterpoise of some type, the feed system always needs two terminals. This is one of Kirchhoff&apos;s Laws. &nbsp;<br><br>Where people go wrong is not understanding the counterpoise and common mode current. The counterpoise can be quite small, a matter of hundreds or thousands of ohms in common-mode impedance. &nbsp;Even a 12-inch square can be an effective counterpoise on 30 meters for an end-fed thin half-wave wire. The problem is a small or no counterpoise creates a counterpoise voltage problem. <br><br>If a counterpoise is small the impedance is high. A small or high impedance counterpoise pumps up in voltage to very high voltages. A small counterpoise has to do this to drive the end of the antenna with the current and voltage the antenna needs. The antenna&apos;s end impedance is high but is finite and dependent on antenna height, cross section (surge impedance), and the antenna surroundings. The feed impedance of an end-fed half wave ranges from hundreds of ohms for a very thick radiator like a tower or tubing to many thousands of ohms for a physically long half wave with thin wire high above the earth. <br><br>But that end impedance is never infinite, so the antenna always requires a counterpoise of some form. We are often blind to the various forms a counterpoise can take, so we develop a false idea &quot;this works fine without a counterpoise&quot;. &nbsp;The counterpoise can be very small under the right conditions. Most of the time the counterpoise is the feedline, and the feedline radiates! At times a feedline can radiate more than the antenna radiates! This can also be proven. &nbsp;<br><br>A high impedance counterpoise will elevate itself to the surrounding world in voltage until it satisfies Kirchhoff&apos;s Laws and the same current flows into and out of the counterpoise terminal as the actual antenna. This current causes an elevated voltage from the counterpoise to the world around the counterpoise. That voltage is what causes the longitudinal voltage that drives unwanted common mode on the feeder, a tower, or a mast that is coupled to the feeder. <br><br>It is actually possible to have, and it can be shown we can have, more current downstream in a counterpoise (intentional or not) because of surge impedances and standing waves. <br><br>It is a crying shame we insist that no counterpoise is required. The lack of counterpoise is the root cause of common mode and efficiency problems. We falsely and repeatedly claim through some magic we can transition from our two or more conductor terminal circuit world to a single terminal radiator without handling that second terminal. This is a major educational problem we should work on. <br><br>Instead, some end-fed half-wave antenna experimenters and educators wrongly tell others a counterpoise is not necessary or required. This misinforms people trying to understand the system and how to make the system work as well as reasonably possible. <br><br>73 Tom W8JI

  49

• DO

  @dougtaylor7724 · 2 years ago

  Jim, you look 1500% better!<br>Great lesson. I’m a picture guy. One picture with explanation is better than a bookshelf full of documents. <br>Thanks for putting these presentations together.

  6

• JA

  @Jackster0729 · 2 years ago

  Hi Jim. Hope you are doing better. Always good to see you here and good luck on W5KUB!

  11

• 1S

  @1stJohn215 · 8 months ago

  Miss you, Jim! &nbsp;You have been a great ambassador for Amateur Radio!

  3

• MO

  @monty2020-i5d · 1 year ago

  This man is such a help. He just knows much important info having spent his life in Ham radio. What a treasure.

  3

• RA

  @RageKge · 2 years ago

  hi jim &nbsp;my name is Keiran im from australia and i just want to thank you for your videos &nbsp;they have helped me keep interested in the hobby as i studied for my foundation level .. i am now licenced and thats thanks in part to fellas like your self, guys and gals taking time to share their knowledge and love for this great hobby.. thank you and 73.. VK4QRM

  2

• MR

  @MrJohnBos · 2 years ago

  I must say Jim that you are looking well, hale and hearty. Thanks for the quick tutorial on antennas, I think I always knew what you are saying but I now have a clear visual explanation about antenna propagation. Wonderful animations.

  2

• RA

  @RayHill-t5q · 9 months ago

  RIP Jim. The Ham world will be forever grateful.

  1

• ED

  @edwatts9890 · 2 years ago

  Nicely explained and nicely presented, Jim.<br><br>There are damned too few of you &quot;REAL&quot; Elmers in the hobby today. Like you, I try to teach, but oh, so many want to enter the hobby with a 1960&apos;s &quot;CB Pirate&quot; mindset.<br><br>God bless you, Brother!

  2

• PH

  @philmaxwell1858 · 2 years ago

  Always informative and understandable. &nbsp;Thanks for taking the time to share your knowledge!

  3

• TH

  @thebuggy736 · 8 months ago

  It is good explained with simple words. Also the animation helps a lot and make it easy to understand.<br><br>Many people have good knowledge but can&apos;t explain it to others.

• CO

  @Coyotehello · 1 year ago

  Always a pleasure to see one of your video poping-up on my YT feed. Thanks.<br>Sweet quick little video.<br>Cheers,<br>a.

  1