# Amateur Extra Lesson 9.3, Antenna Systems

Here’s your video introduction to Section 9.3, “Antenna Systems,” in the ARRL Extra Class License Manual for Ham Radio. Topics covered include impedance matching of transmission lines to antennas, how transmission lines work, including electrical length, propagation velocity, loss, reflection coefficient, standing waves, also the Smith chart, transmission line stubs, synchronous transformers, and antenna analyzers.

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### 2 Responses to Amateur Extra Lesson 9.3, Antenna Systems

1. Dave says:

Hi Neil! And I was so careful with the example at minute 17! I’m looking at my notes now, which I saved along with the script. Regarding the terminology, note that the line is not terminated, but rather there’s an impedance mismatch between cables. The question becomes how much power out of the total power from the transmitter is reflected back toward the transmitter, and how much continues forward. Regarding the 0.02, you’re absolutely correct. It’s correct in my notes as 0.2, but when I transferred it to the drawing, an extra zero slipped in. And then I wrote the script after I made the charts, and so perpetuated the error. I’m going to make a note on the YouTube video description. And you’re right about the opportunity for terminology confusion. I commend you for your good catch – the video has been viewed over 3,000 times since it went up in May, and you’re the first to catch the error! I suspect you’ll have no trouble with the test! 73, Dave, KEØOG

2. Neil says:

Hello Dave,

Re: Possible error at 17 mins in the slide on reflection coefficient

I’ve been watching your videos over the past few weeks while I’m studying for the Canadian Amateur Basic and Advanced exams (there seems to be a lot of overlap with the US exams — some of the questions in the question banks are even verbatim the same! — although there doesn’t seem to be much rhyme or reason as to which question goes in which exam).

Thank you very much for the videos, you’ve done a great job of them, and they’ve made some enjoyable study breaks for me.

I seem to have spotted an error at about 17 minutes in to this video (Amateur Extra Lesson 9.3, Antenna Systems) on the slide about the reflection coefficient, rho.

First of all there seems to be a fair bit of scope of confusion for the viewer from the multiple terms used for the incident energy: your voice says “incident” while on the diagram it is labelled “applied” and in the equations for rho in terms of current and voltage you have “total”; perhaps that’s an opportunity for clarification if you do another edition of the videos.

Secondly, the equation for rho in terms of power feels wrong. Shouldn’t it be _incident_ power in the denominator not _forward_ power?

Thirdly, root(4/100) [or root(4/96] is 0.2 [or 0.204] not 0.02 as stated.

Thanks, and best regards,
Neil.