Wednesday, April 4, 2012

A Moving Experience

Thought for the day: A little boy refused to run track in his gym class anymore, and when his mother asked him why, he said, "My science teacher said the faster something goes, the shorter it becomes. 

[THEME: Amateur radio]

Today, we're gonna talk about the DOPPLER EFFECT. 

Sound familiar?

Maybe you heard about it on one of my favorite TV show, The Big Bang Theory.



                                                  Well, then you HAVE to watch this:

The most common example used to describe the Doppler effect is a siren:

Have you ever noticed that the frequency of a siren's wail changes, depending on how close it is to you? The farther away it is, the lower the frequency, and the closer it is, the higher.

                                                                   Ever wonder why?

Let's say I'm that little red dot in the center of that diagram. And I'm a beetle, one of those amusing ones who  bangs its foot to make noise to attract a potential mate. With me so far? So, when I'm thumping away, the sound waves travel out equally in all directions. Assuming potential mate A and potential mate B are equidistant away from me, my come-hither sound wave will take the same amount of time to reach each of them, and they will each hear it at the same frequency.

But suppose potential mate A, who is located towards the right side of the diagram, responds with a sexy sounding thump of his own? Well, natch I start hustling in that direction. (I may be a beetle, but I'm no fool.) As I move away from B, who is on the left, it will now take longer for the sound of my thumping to reach him. (I'm multi-talented; I can run and thump at the same time.) As I approach A, my sound waves take a shorter and shorter time to reach him. That is, they come at a higher frequency. And for poor he-who-hesitates-is-lost suitor B, the waves take longer, and are at a lower frequency.

Make sense?

So, what does that have to do with amateur radio, you may ask? Amateurs can communicate via satellite. Or with a space shuttle, or the space station. Which are all moving, right? So, the satellite's frequency changes as it moves across the sky, and amateur radio operators must track that change, and coordinate their radio's frequency if they want to make a successful contact. Cool, huh?

And no, we don't have to do it by guesswork, either. There are some terrific computer programs specifically designed to track satellites and calculate this information.

(But ya know, I still like Sheldon's explanation the best ...)


  1. The way allergies have effected my hearing lately, it's a good thing I'm not a beetle, lol!

    Sheldon is a cute dork and the clip cracked me up.

    Looking forward to the next installment!


  2. Doppler was one of the few things that interested me in my school-days science class.

  3. and that endeth the lesson for today!

  4. That was very well explained. It is always a good day when you learn something new.

  5. great post for A
    do check my D at GAC a-z

  6. I've learnt something new today (and I thought he was a bar code!).

  7. Sua- HA! I know what ya mean!

    Cro- Well, good. That means, if I messed up the explanation, you could've corrected me. (You didn't, so I guess I didn't!)

    John- Yeth, thir, it doeth. (But there's always tomorrow!)

    Arleen- Super. Not that I think of myself as a teacher, exactly. More of a de-mystifyer.

    Pa- Thank you. Will do.

  8. Sarah- HA! He does kinda look like one, doesn't he?

  9. Remind me to never stamp my feet. I love Big will be a sad day when they decide not to renew it.

  10. Like all your posts, this was both educational AND entertaining! Great job, Susan!

    You rock!

  11. I've never had trouble understanding this, but I must say: that graph with the moving red dot makes it eve clearer.


  12. Delores- On the plus side, if the network is ever foolish enough to cancel "Big Bang", it'll be forever reincarnated through reruns.

    Chris- Thanks! You made my day!

    Matt- Visuals help when I don't wanta use a thousand words. And thanks for stopping by. I know this challenge has kept you busy.

  13. Very good explanation. I need to send that quote to my science teacher Dad. He will love it. :-) Have a great day!

  14. Hi, Susan. I am working very hard right now to have a crystalline understanding of frequency, wavelength, bandwidth and modulation.

    Have you read/heard of ?

    It's one of my textbooks, at the mo.

  15. Sheldon's explanation really brought it home for me. That and his zebra outfit. ha!

  16. Tracy Jo- Glad ya liked it. And I hope you dad likes the quote. You have a great day, too!

    Suze- Well, once you understand those concepts, you'll almost be ready to take your test to become an amateur radio operator! I've heard of that book, but haven't read it. Have a bunch of other similar ones around here, though.

    Tina- Sheldon is absolutely priceless. Thanks for stopping by.

  17. I love the graphics. It helps to get a visualization on this effect. As to the "Thought for the day", I must remember to slow down when my wife and I make love.

  18. i enjoyed learning about the doppler effect. too bad this doesn't work for humans :)
    great a-z post!

  19. Loved that clip! Hadn't see it before.

  20. I think I actually learned something, but don't worry -- I'll forget it in a few hours.


  21. G. Thomas- HA! Leave it to a guy to come up with that one!

    Nutschell- Now, wouldn't THAT be funny? People would be all over town thumping their feet. Not sure, but I think humans do more hip-swaying and eyelash-batting. Thanks for stopping by.

    Jennifer- Glad ya liked it.

    Janie- Nah, you won't forget. Just think about the bug. Ya know, today's post had the "Big Bang" and the "bug bang". Just think about the bug.

  22. This brings back memories of freshman physics. @.@

    Happy A-Z!

  23. What is all this stuff? Doesn't sound like "amateur" radio to me. Computer programs, taking to satellites? I thought amateur radio was two tin cans and a string. Or a crystal set.

  24. I was wondering how the Doppler Effect was going to play into the theme. So interesting! And the clip was funny, thanks for the laugh. :)

  25. McKenzie- Not sure if reminding you of physics class is a good thing or not, but thanks for stopping by. Happy A-Zing to you, too.

    Mr.C- HA! Amateur radio is all kinds of stuff. I hope I give you a few more surprises.

    Julie- Glad you liked the clip, and I'm reeeally glad you're still finding this stuff interesting. Who knows? Maybe you end up being a fellow ham-ster.

  26. Any in particular you recommend?

  27. Suze- If you can get your hands on an old ARRL (American Radio Relay League) "Now You're Talking" book, which used to be the entry level study guide for amateur radio, it does a real good job of explaining the concepts in simple terms. I'm sure the more recent technician study guide is good, too, but I've never used it to teach a class, so I can't personally vouch for it. But bottom line, all of the things you're trying to understand right now are basics every ham has to learn about to get a license, so any intro book to amateur radio should be helpful to you. There's even a "Ham Radio for Dummies" book out now, and it must be pretty good, because some of the guys I know have used it as a textbook in classes they've taught. You might even be able to find that one in your local library. Most of the other books we have around here are more advanced and kinda pricey, but if you're interested in books with more in-depth electronics, etc, I'd be happy to recommend some of them.

  28. Thanks so much for this, Susan. I saw 'Ham Radio for Dummies' in the bookshop but opted for the one I linked in the comment, instead. I plan to look up the, 'Now You're Talking,' book. It's easier than ever to locate older texts now through all the different online venus.

    Again, thanks!

  29. Suze- One caveat. If you think there's a possibility that you might want to pursue getting your amateur radio license, don't use the "Now, You're Talking." It's great for all the basic principles you want to understand, but the band plan and some FCC rules and license requirements have changed since that book was written.

  30. Hi Susan .. I had concentrated my mind on this - but it makes absolute sense - and I'd heard of Dopler, but not sure what it was .. amplification yes .. but specific .. ok - so now I can go find me a beetle .. or a radio operator ..

    It's very interesting this series ..

    Cheers Hilary

  31. Hilary- Glad you find this theme interesting, and glad you have a better understanding of the Doppler effect now. Cheerio!