Pigtails, Coax and Velocity Factors (044)

In the process of preparing to create a video on making your own 4:1 BALUN using coax, a question came to mind.
{NOTE: I will insert the promised link to the 4:1 BALUN video when I get it uploaded and ready to go}
We have to have a way to connect our 4:1 BALUN to the antenna -- pigtails of some sort (?).
In my experience of making these BALUNs, the BALUN coax ALWAYS had to be a bit longer than the calculated value. WHY?
Then there is the standard equation for Velocity Factor which makes no mention of coaxial shields, just the Relative Dielectric Coefficient of the insulation.
The point of this video is to investigate this phenomenon and to give us a way to better predict the length of coax needed to get the electrical length we want if some sort of pigtail is going to be required in our design such as with the 4:1 BALUN.
While high-end math could be meticulously applied to the subject, I am focusing on the end result and what the average experimenter is interested in: practical application and how do I do this without a PhD in Mathematics.

Time Markers for Your Convenience
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00:05 Initial Comments and Introductions
01:07 Why this video? What made me wonder?
02:34 How am I going to do this experiment?
03:26 The Experiment
03:34 Step#1: Measure the Velocity Factor of my Coax
03:50 High & Low Scan Limits
04:04 The Setup
04:44 Doing the Port Extension
06:17 Measuring the Velocity Factor
07:55 Calculating the Velocity Factor
08:50 Step #2: Stripping the last 4 inches or 10.16cm
09:04 Measuring the NEW Velocity Factor
09:34 Calculating the NEW Velocity Factor
10:09 What does all of this mean?
12:47 Final Comments and Toodle-Oots
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[elmoreglidingclub]

Thanks for a great video. I’m a new ham and am finding that antennas are profoundly interesting. After erecting a 40m insulated copper wire inverted V dipole, and trimming for minimum SWR at 7.034, I began searching to learn why the legs were shorter (at 29’6” each) than the calculations suggested. That has taken me down the very happy rabbit hole of velocity factor! So thanks for this.

[milesprower]

How would I measure antennas and devices that use 75 ohm coax with the nanoVNA? I always get tons of ripple measuring swr

[dennisqwertyuiop]

what vna are you using ? i have the nano, , the only thing i dont have is a vna like HP, , its on my list

[Brenda-jfpe]

Imagine the slide rule guys doing this, like 50 years ago! Thank computers thank you AI! JohnBoyUtah KJ7TBR