Antenna Feedline Optimal Length for Resonance

Updated 4-18-2024

I recently discovered a YouTube video that shows how to cut an antenna’s feedline length to achieve resonance (See below). I then discovered that there are many such erroneous YouTube videos telling you that you can use “jumpers” to improve your antenna performance. There are no benefits to these practices! But this begs the question… Why? On the surface, it makes sense. Assuming that a given antenna installation is showing a vector impedance of something other than 50 + j0 Ohms, either adding or subtracting an optimal antenna feedline length will give pure resonance, completely nulling out any reactance. Nobody questions that. But here is the big BUT…the effective SWR will remain unchanged regardless of what feedline length is used.

Chelsea Amateur Radio Club Presentation Announcement

Have you heard claims that an antenna’s feedline length can be optimized for resonance suggesting an improved antenna performance? At the June 11th, 2024 meeting of the Chelsea Amateur Radio Club we will have a presentation using the Smith Chart to show that such claims are not valid.

Briefly, Here is Why You Should Ignore these Claims

Continuing my search, I found several other YouTube videos of the same nature, all with reference to citizens band (CB) radio. They call them “jumpers” which you add to your feedline.

While this video may not be giving you bad advice, it is advocating worthless “optimizing” techniques.

Ironically, they are on the right track but have completely and 100% missed the boat. A tuning stub will accomplish what they are likely trying to do. But the “jumper” required does not resemble what they are solving for other than it is a hunk of coax cable. The cable that they are “cutting to length” will, in all cases, be of no use. We gave a detailed presentation on tuning stub design at the September 13th, 2022 Chelsea Electromagnetics-for-the-Masses class.

At the June 2024 meeting of the Chelsea Amateur Radio Club, Wes Cardone (N8QM) will give a presentation using the Smith Chart to show why a feedline length is not directly relevant to an SWR. The preliminary presentation handout is shown below, but please check back later as there are certain to be updates.

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