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posted by hubie on Monday April 01, @06:50AM   Printer-friendly
from the how-to-ham-it-up dept.

https://lcamtuf.substack.com/p/radios-how-do-they-work

Radio communications play a key role in modern electronics, but to a hobbyist, the underlying theory is hard to parse. We get the general idea, of course: we know about frequencies and can probably explain the difference between amplitude modulation and frequency modulation. Yet, most of us find it difficult to articulate what makes a good antenna, or how a receiver can tune in to a specific frequency and ignore everything else.


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  • (Score: 3, Informative) by julian on Monday April 01, @07:30AM (7 children)

    by julian (6003) Subscriber Badge on Monday April 01, @07:30AM (#1351163)

    I am studying for my amateur radio license and this was interesting and useful. It's been 20+ years since I took an electronics class in high school, and a decade since college physics, but a lot of it came back reading and watching this.

    • (Score: 5, Insightful) by JoeMerchant on Monday April 01, @01:28PM (6 children)

      by JoeMerchant (3937) on Monday April 01, @01:28PM (#1351191)

      I took the electrical engineering undergraduate curriculum in the 80s. They instill a great deal of confidence in knowing how radios work, from AM/FM modulation, through heterodyning, phase lock loops, stereo encoding (L+R with side band L-R), some waffle about the various ways of doing quadrophonic, but then you come to antennas....

      Most anyone can tune a dipole. There are some well studied designs out there like the groundplane vs quarter wave upright, directional yagis, etc. but, the main takeaway from the Smiths' charts class was: unless you want to devote a LOT of time to the subject, just use off-the-shelf designs - even they are just a lot of well studied VooDoo.

      Any random bit of wire makes an antenna, whether you want it to or not. How those random bits relate to the resonant frequency of themselves is more mystery than science.

      --
      🌻🌻 [google.com]
      • (Score: 5, Interesting) by RS3 on Monday April 01, @02:58PM (2 children)

        by RS3 (6367) on Monday April 01, @02:58PM (#1351198)

        Very similar story here, although in my undergrad BSEE we did more theory, including antennas and wave propagation, which really wasn't my thing and I barely got through it. I remember hating Green's and Stoke's theorems (3-D integral calculus transforms or something like that). But the more seat-of-the-pants stuff- everything up to EM wave propagation was good for me. I'm more than willing to relinquish such studies to the more mathematically-inclined. I do better with stuff I can see and understand. My oscilloscopes allow me to see signals, so that counts too. EM waves, I can imagine, but...

        When I learned of the multi-element planar antennas, then ceramic resonator antennas, I gave up completely and went and changed some spark plugs. Now I have a lazy O2 sensor to deal with...

        • (Score: 5, Interesting) by JoeMerchant on Monday April 01, @03:39PM

          by JoeMerchant (3937) on Monday April 01, @03:39PM (#1351203)

          I did the advanced integral calculus stuff ... path integrals around singularities on Gaussian surfaces not adding up to zero and all that jazz, aced the class and promptly forgot it all - never seemed to need it back.

          Later, I did do heating studies for implantable neurostimulators inside MRIs. You might attempt to model/simulate that with a really advanced FEA system, but this was 2005 and the numerical methods approach wasn't really ready for the task yet. Even today with the equivalent of all Top 500 supercomputers from 2005 thrown at the simulation - your antenna of concern is inside the human body, laying across and along rib bones, under skin, with flowing blood all around. The antenna itself is a coiled spring that is laid in an arbitrary-ish 3D swirly shape that's different for every patient, and it's got funky platinum electrodes wrapping a nerve on one end and a whole pulse generator system on the other end. Whatever your FEA result comes to will apply for that one case, and small changes are possible to result in big differences of outcomes. Then you can start to talk about the different field strength patterns in the various MRI bores and their various pulse sequences...

          We simulated the patient with a tub (torso-head simulated in rectangular form) of saline gel slurry and approximated the surgical implantation with a plastic frame in the tub. We did hundreds of in-MRI tests where we measured heating at the electrode tips, and in all tests but one there was nominal non-injurious heating at the electrode tips. Except... one particular test managed to get the lead wire into a resonant configuration and the heating ran wild. A wiser head than mine called halt to the test after the heating crossed the injurious / failure threshold - a fail is a fail, we didn't need to demonstrate sparks or flames or boiling gel, which I suspect we would have at least gotten to boiling gel if we had continued another 30 seconds. MRI RF excitation pulses are really strong, people get hot and sweaty more or less like they've been in a (mild) microwave oven during the longer abdominal / spinal imaging sequences. It's not ionizing radiation, but neither is your microwave oven - hopefully.

          --
          🌻🌻 [google.com]
        • (Score: 4, Interesting) by corey on Monday April 01, @11:15PM

          by corey (2202) on Monday April 01, @11:15PM (#1351257)

          Yeah I hated all that heavy mathematical stuff and struggled with it. I did well in labs though. But all that analysis doing volume integrals and covering that to surface flux integrals etc… Eugh. But I get the point. I can fully understand and remember and picture Maxwell’s equations.

          Anyway I went off and became an electronics hardware engineer, and never used any of those equations ever again. I’m getting into RF more these days but again there are quick equations and rules of thumb, lookup tables etc which make things simple.

      • (Score: 2) by Beryllium Sphere (r) on Tuesday April 02, @02:11AM (1 child)

        by Beryllium Sphere (r) (5062) on Tuesday April 02, @02:11AM (#1351285)

        Whether it's practical to try new antenna designs or not, it's certainly fun to use EZNEC.

        • (Score: 2) by JoeMerchant on Tuesday April 02, @11:21AM

          by JoeMerchant (3937) on Tuesday April 02, @11:21AM (#1351329)

          Yeah, I don't think EZNEC was available on PC in 1987.

          FEA can also do some amazing things these days.

          --
          🌻🌻 [google.com]
      • (Score: 3, Informative) by kazzie on Tuesday April 02, @08:29AM

        by kazzie (5309) Subscriber Badge on Tuesday April 02, @08:29AM (#1351316)

        It's a step below undergraduate stuff, but the college-level electronics courses I teach have NOTHING radio in them at all. Basic principles, breadboarding, fault-finding, solder and rework, product design, electro-pneumatics, embedded systems, PLCs and industrial robots, but radio and communications is a notable gap in the course.

  • (Score: 3, Funny) by turgid on Monday April 01, @09:49AM (6 children)

    by turgid (4318) Subscriber Badge on Monday April 01, @09:49AM (#1351175) Journal

    When I was about 7 I asked the school janitor how the bell worked. "There's a wee manny inside wi' a hammer!"

    • (Score: 1, Funny) by Anonymous Coward on Monday April 01, @10:48AM (1 child)

      by Anonymous Coward on Monday April 01, @10:48AM (#1351178)

      You went to Springfield Elementary to!?

      • (Score: 3, Funny) by Gaaark on Monday April 01, @11:29PM

        by Gaaark (41) on Monday April 01, @11:29PM (#1351261) Journal

        You went to Springfield Elementary two!?
        ;)

        --
        --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
    • (Score: 2, Funny) by Anonymous Coward on Monday April 01, @01:40PM

      by Anonymous Coward on Monday April 01, @01:40PM (#1351193)

      That tolled you.

    • (Score: 3, Funny) by RS3 on Monday April 01, @03:00PM (2 children)

      by RS3 (6367) on Monday April 01, @03:00PM (#1351199)

      Not sure if you ever saw the cartoon "The Flintstones". I remember the camera they had- there was a little woodpecker inside that would peck out the desired picture. Even as a young child I thought that was pretty funny.

  • (Score: 5, Funny) by Rosco P. Coltrane on Monday April 01, @11:07AM (1 child)

    by Rosco P. Coltrane (4757) on Monday April 01, @11:07AM (#1351179)

    many decades ago started with "Imagine you're trying to watch TV while your wife is shouting at you. That's tuning."

  • (Score: 3, Funny) by darkpixel on Monday April 01, @06:46PM (3 children)

    by darkpixel (4281) on Monday April 01, @06:46PM (#1351216)

    My dad taught about electricity and that it's tightly linked to radio.

    He said:

    It works off a technology called FM. I don't remember what the 'F' stands for, but the 'M' stands for 'Magic'.

    • (Score: 3, Insightful) by JoeMerchant on Monday April 01, @10:40PM (2 children)

      by JoeMerchant (3937) on Monday April 01, @10:40PM (#1351253)

      >It works off a technology called FM. I don't remember what the 'F' stands for, but the 'M' stands for 'Magic'.

      I'd throw out there: it actually stands for Farkin' Math. I'll grant that the average bear doesn't have any need of the level of mathematics required to Grok Frequency Modulation, but I will submit that the average bear probably could take a few courses beyond where they ditched higher mathematics and get a pretty good feel for how Magic really = Mathematics, if they wanted to.

      It's not "out there" like brain science or rocket surgery.

      The neurostim company I worked with hired a Harvard M.D. Neuroscientist to advise on our technology and (let's get real...) how best to make more money from it. His most insightful comment on the latest (2005) maps of brain function and understanding of the best luminaries in the field of brain science was: "they're pulling at least 90% of what they write straight out of their asses."

      --
      🌻🌻 [google.com]
      • (Score: 2) by turgid on Tuesday April 02, @08:38AM (1 child)

        by turgid (4318) Subscriber Badge on Tuesday April 02, @08:38AM (#1351318) Journal

        One of my greatest regrets in life is letting my Maths skills go rusty. I used to be really good at it. The trouble is, you need to do a bit every day to keep the skills sharp. That's mostly doable when you're at school but I found that grown up life is to unpredictable and tiring to be able to do that. I have gone through periods when my coding skills have almost withered away to nothing. I once was good on the bass guitar too. I've tried to learn the six string several times, and kept it going for months at a time but then life gets in the way.

        • (Score: 2) by JoeMerchant on Tuesday April 02, @12:18PM

          by JoeMerchant (3937) on Tuesday April 02, @12:18PM (#1351334)

          I have practiced piano and ukulele long enough to realize that I will never be "good" at either one... Better than people who never studied or tried, sure, but still far from good. Part of the problem is that I can hear how bad I am, more in rhythm than tone.

          The "bigger math" I have done over the years tends to be stuff you won't find in a book or online reference, but you can derive it from nearby well established principles... Like: determine a 5th order polynomial best fit to a set of arbitrary data points plus two end points with flat entry and exit slopes... That took all day to derive in the first place and four more hours to translate into code and fix the mistakes. Then there was: given two (rectangular box) counter-rotating arms with nested rectangular box weights on their ends, size the arms to max radius for 1/4" clearances and size the outer weight box to dynamically balance the counter-rotating system in two dimensions (all boxes cut from bar stock, so only one calculated dimension per box...). When I got that one done I tried to look up my Undergrad physics prof from ten years earlier to share and thank him, but he had retired and disappeared.

          --
          🌻🌻 [google.com]
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