Smith Charts: DEMO 2 - Folded Dipole Parallel Stub Match Design & Build (00h9)

Not all antennas have a 50 Ohm impedance at resonance. A folded dipole is a case in point. Using your Smith Chart, you can design and build a matching network to transform your antenna impedance to your feedline impedance.
In this demonstration, I design, build and test a Parallel Stub Match to match an old experimental folded dipole to my 50 Ohm feedline for the 2 meter amateur radio band.
The result?
Less than a 1.12:1 SWR across the entire band.
00:05 Introduction
02:36 Start the Process
02:45 Showing the Folded Dipole to be matched
03:29 STEP 1 = Measure the actual Impedance
06:41 STEP 2 = Know Your Coax (Measuring the Velocity Factor)
07:08 Measuring coax Velocity Factor with a VNA
09:44 All the Facts in One Place - What are we working with?
10:19 STEP 3 = Normalize your measured Impedance
10:49 STEP 4 = Plot the Normalized Impedance on the Smith Chart & draw the SWR circle
12:44 STEP 5 = Convert the Impedance to Admittance using the Smith Chart & read lambda(load)
14:14 STEP 6 = Move to the G = 1.0 Circle & read Admittance(a) here and lambda(a)
15:57 STEP 7 = Calculate coax length from Load to Stub (Impedance Transforming)
17:52 STEP 8 = Determine the lambda(Stub)
21:41 STEP 9 = Calculate the length of the coax for the Stub (Reactance Eliminating)
22:47 CONSTRUCTION BEGINS - Introduction
23:27 On the bench - important things to remember in construction
26:28 How to make the SHORTED end of a SHORTED Stub
27:29 How to make the OPEN end of an OPEN stub
27:43 The completed Stub Match - A Tour
28:05 Testing the Stub Match with the Folded Dipole
28:23 Initial Test Results and final adjustments
29:45 Final comments and Toodle-oots :-)

[luckymunkey.]

Mr Ralph.

You have given me some great info on how to further learning. I will check out the arrl website. Also I will keep learning and watching your videos. Thank you and keep sharing the knowledge.

[PatAutrey]

This is exactly what I was looking for thank you so much!

[luckymunkey.]

I enjoy your videos Ralph. I have a question. As me being a truck driver I’m not home a lot. But I was wondering if you know any courses online or information I can read to learn more about working on my own cb and antenna system. Your videos have taught me a lot. I was just looking for more info to go in depth.

[andreifiadziushkin]

Hello Ralph. Does this mean that your antenna is not really resonant at 146 MHz because of the high imaginary part of the impedance? As I know, having VSWR close to 1 does not necessarily tells us that antenna is resonant at a given frequency. Thank you very much for the matching part of your video. This is really helpful.

[orhuk]

Is it possible to do all the calculation with nanovna instead of by hand?

[nirbhay_raghav]

Hey Ralph, really insightful video. Can you please help me out with something? I am working with a fded dipole for VHF. It was already tuned before by someone else and has a single stub for matching. The thing is that I am not sure how it is connected. It does not make any sense to me and has flipped the entire knowledge of my antenna theory by 180. The stub is shorted to inner conductor on one end. But the other end in theory should be shorted to the outer end but it is not!! The other end of the stub (the one not shorted to inner) just goes and connects to the other end of the folded dipole. But the thing is that antenna works. Can you help me out? Or point me to a reslurce which can help me