Matched Listening Antennas – Why?

Antenna

I had a revelation the other day regarding listening antennas.

As a ham I am very well aware of the importance of SWR and matching antennas to transmitters. Well enough versed in fact to never have worried about it too much. An Elmer I had in the 1970s told me, whatever power is reflected back from your antenna to your transmitter will meet a mismatch there as well, and will just get reflected back to your antenna system, and will be radiated. Don’t worry about it he said, unless you’re running VHF or higher, or your transmission line is extremely lossy.

I have seen this wisdom repeated by knowledgeable folks here and there and trusted this advice for decades. It has served me well.

Here’s the revelation part. Whenever is has come to receiving antennas, I have never given much thought to resonance, matching or anything of the like. I’ve always had good results from attaching a random length piece of wire to my shortwave receiver and enjoyed good results. Or so I thought. I even wondered to myself why SWLs even bothered to worry about resonance or feed-lines? It only mattered when transmitting in my book. I think I was wrong now.

RF coming into your shack via some feed-line will meet your radio at whatever impedance it presents. Yes, if there is a mis-match, RF energy will be reflected back up the feed-line. Here’s the very important point- Once reflected back to the antenna system, the majority of the energy will be radiated out of the antenna!

I never considered that before. I figured, I’m receiving only, nothing is getting transmitted here. Bouncing RF will end up in my radio. That, is a wrong assumption. We might only be talking about micro-volts, but your antenna is transmitting reflected energy! It suddenly makes sense. Now I know why “those guys” worry about this stuff!

1 thought on “Matched Listening Antennas – Why?”

  1. Dear Rick, First I want to thank you for putting out quality blog posts, a lot of hams are just a little scared to write content about his or her adventures in amateur radio.
    Now to the reason I am writing this this comment. I am the editor a free electronic newsletter called Short Skip published for my local amateur radio club(W9LJ.org) and some local friends that wish to stay out of clubs. And I am looking for content to fill pages. Over time it has been getting harder and harder to find local people to write and fill the alotted 10 pages of our small newsletter, so I started asking people who has already written content on ones blog. Why am I asking? Well I dont want to take content without asking, its not polite. Here is what I would like to do, publish your work and give you attribution of the work in the manner specified by you the author. Unforchantly we cant pay for content, that is one reasons why Short Skip is free of advertisements and free to read. I don't even get paid and wouldn't want to.
    If you wish not to allow us to use your content, that's fine, just let me know, Oh and keep writing good content for us to read.
    Thanks and 73,
    P.S. You can email me back via my call sign below at gmail.com

    Benjamin A Straw – KC9UNS
    Editor – Short Skip LCARC Inc W9LJ.org

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