In this video I will be showing you how to get an estimate of the impedance of antenna or other load at the other end of a feedline.
So, you have an antenna at the top of a tower. You know the length of feedline between it and you. You know the type of feedline and its velocity factor.
You measure the impedance at the end of the feedline you are at.
With this procedure, you can back-calculate the antenna's impedance without having to climb the tower.
I will present the **FUN** way and the EASY way.
Because this is non-ideal feedline, it will be a reasonably close estimate, but not the kind of spot-on precision you would get if you measured it right up close and personal like.
I *strongly* recommend that you use a nanoVNA, miniVNA tiny, high-end VNA or similar device to measure impedance. I have not had good experiences getting accurate impedance measurements using the average antenna analyzer.
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TLW Settings used for the Easy Way
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Cable Type: RG-8A (Belden 8237)
Feet
Length: 76.167 feet
Frequency: 10 MHz
Source: * Normal
* Input
Resistance: 63.58
Reactance: -2.69
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==== PROMISED LINKS ======
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Downloadable, FREE Smith Chart
[ Ссылка ]
TLW, Transmission Line Program for Windows, FREE downloadable ZIP file
www.arrl.org/files/file/QST%20Binaries/June2014/TLW3.zip
Time Markers for Your Convenience
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00:05 Initial Comments & Introductions
01:45 The *FUN* way ...
01:56 What do I need to know?
03:12 What are we going to be doing?
03:18 The Test Load
03:39 The Feedline
03:57 Where is the Test Load?
04:04 Where are we measuring from?
04:11 Our final goal
04:23 Preparations
04:29 Calculate the Feedline's Electrical Length
05:12 Measure the Impedance at the End of the Feedline
05:35 The Smith Chart Itself
05:46 STEP 1: Prepare Feedline Wavelengths
06:25 STEP 2: Normalize the Measured Impedance
06:52 Plotting on the Smith Chart
07:41 Step A: Plot the Normalized Impedance
07:47 Step B: Draw the SWR Circle
07:57 Step C: Draw the Line Center to Edge through the Z
08:07 Step D: Note the Wavelength Value on the Edge
08:17 Step E: Moving Around the Smith Chart
08:52 Step F: Mark the New Wavelength Point
08:58 Step G: Draw a Line from the New Point to the Center
09:10 Step H: Note where this New Line Crosses the SWR Circle
09:15 Step I: Determine the Normalize Impedance Value at that Spot
09:32 Step J: Un-Normalize the Impedance
10:25 VNA Cal at the End of the Feedline, Measured Impedance
11:04 The **EASY** Way
11:38 The Results?
12:26 Final Comments and Toodle-Oots
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