Math problem for a few local hams - they couldn't do it - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: October 16, 2019, 11:36:45 pm
content: It all started with this simple equation that hams use to calculate wavelength -λ=c/fWhere -λ=wavelength in metersc=speed of light 300,000,000 m/s (normally just rounded up from 299,792,458 m / sf=frequency in HzIn ham radio its been simplified by dividing c & f by 106and just using λm=300/fMHzSimple enough.In the hf bands there is one frequency that has the same numerical value for both it's frequency and it's wavelength (not the same units of course). It's 17.321 MHz, which has a wavelength of 17.321 meters. I was asking some local hams on the repeater to re-arrange the equation using a little ingenuity so as to be able to simply enter a few keystrokes on a calculator and get the answer - it requires no more information than is in the equation. They didn't already know the answer either. I specifically stated that theactual answeris not what I want because any trained monkey can Google it. No, I want to see how you can get it from the equation directly by doing a little algebra.It basically reduces to x2= 300, therefore x=√300.They are all (so far) dumbfounded as to how to do it. One guy, when I asked him to try, never even hesitated and just instantly gave up - "I can't do that kind of stuff". No one has solved it.Remember, these are technical people. Am I naive or is our population losing the ability to do high school math? How is it that hard? Am I being unfair asking this sort of thing of them? I really didn't mean to "show off" I thought they would be able to do itThoughts?

author: IanB
author_rank: Super Contributor
timestamp: October 16, 2019, 11:44:19 pm
content: Quote from: xrunner on October 16, 2019, 11:36:45 pmI don't think you should assume ham radio people are technical people. You should just assume they are people who like playing with radios and talking with other people over the airwaves.There are certainly some radio enthusiasts who would have no trouble with that problem (I know one). But sadly many people who are not engineers or physicists or something like that have limited math skills.

author: soldar
author_rank: Super Contributor
timestamp: October 17, 2019, 12:27:02 am
content: Quote from: xrunner on October 16, 2019, 11:36:45 pmThe equal sign is overrated.Things can be equal if they want to, or if they are equal they can be not equal in other ways. Diversity is equality.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 17, 2019, 12:47:16 am
content: Quote from: soldar on October 17, 2019, 12:27:02 amTrue New Age thinking!

author: xrunner
author_rank: Super Contributor
timestamp: October 17, 2019, 12:54:10 am
content: Quote from: IanB on October 16, 2019, 11:44:19 pmPerhaps you are right. It's a formula that hams are taught and use, and they understand how to use it as long as it's got one of the variables already filled in that they need. Oh well ...

author: amyk
author_rank: Super Contributor
timestamp: October 17, 2019, 01:22:53 am
content: Throughout the years there hasalwaysbeen a group of hobbyists who never bother to dig deeply and understand things; kit-builders, hams, then the Arduino crowd, now the RPi and its community.

author: Circlotron
author_rank: Super Contributor
timestamp: October 17, 2019, 01:41:40 am
content: So, is 17.321 metres/MHz the golden ratio of RF?

author: bob91343
author_rank: Super Contributor
timestamp: October 17, 2019, 02:22:55 am
content: Notice that the 17 meter ham band is at 18 MHz, close enough. If it were the 18 meter band it would be at 17 MHz I guess. So the square root of 3 is 1.732 and that's the answer.

author: james_s
author_rank: Super Contributor
timestamp: October 17, 2019, 02:43:57 am
content: Quote from: amyk on October 17, 2019, 01:22:53 amI think that's overly generalizing, there are people of all skill levels in each of those crowds, it's just that all of these categories lower the barrier of entry which enables people other than the hardcore technical crowd to participate.I see the exact same thing in the RC airplane community, elitist old guys who look down their noses at anyone who doesn't painstakingly build their planes from balsa sticks, ignoring the fact that the hobby would have likely died out entirely if not for the plethora of inexpensive "foamies" and other nearly ready to fly models one can buy today. The hardcore enthusiasts are still around, they're still free to do their thing, but now a much larger range of people can participate and have fun. Personally I see nothing wrong with this, everyone has different interests in life and I don't think the fact that someone lacks the time, motivation or mental acuity to dig deep into the fundamentals should preclude them from being involved. There's a lot more stuff out there for people to do these days, can't dive deep into all of it.It's a hobby after all, the whole point is to have fun.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 17, 2019, 03:13:18 am
content: Most US hams use a "magic formula" to give the wavelength in feet, when they are building antennas, so aren't all that familiar with 300/f where f is MHz, & wavelength in metres, let alone the full version.The oldtimers knew the real formula, but the "number crunching" was harder to do in your head, so the antenna formula, "half wavelength in feet = 468/f, which you will see in the ARRL publications, & echoed across the Internet was derived.This includes correction for "end effect", shifting the person using the formula one step further away from the original.With the proliferation of calculators, both real & "Apps", there is no longer any reason for this "crutch",but it has become part of the fabric of ham antenna building.The silly thing is, when you see an Australian ham, born years after metrication in this country, using 468/f, then converting the answer to metres.

author: hamster_nz
author_rank: Super Contributor
timestamp: October 17, 2019, 03:54:48 am
content: Although interesting, the answer is of very little impact, other than as a fence post when approximating.It is a bit like how I know how to calculate celling(log2(x)) as if by magic, and could moan that most programmers only have a intuitive feel for 256, 65,536 and 4,294,967,296Physicists would put us all to shame, as the rescale and recast things to different basis vectors, so the answer is always "oh, that is just a+b or a*b" hence weird values like MeV for mass.

author: thinkfat
author_rank: Unknown
timestamp: October 17, 2019, 07:30:18 am
content: You're not required to know any algebra for passing a ham radio examination.You need to learn regulation, lots of, and a little bit of Ohms' Law, but that's about it.That's about as technical as it gets. Yes, there are very technical people amongst HAMs, and then there's even more who just browse Kenwood or Yaesu catalogs

author: fourfathom
author_rank: Super Contributor
timestamp: October 17, 2019, 07:47:51 am
content: Quote from: thinkfat on October 17, 2019, 07:30:18 amThat depends on the ham license. I vaguely recall that about 45 years ago my (USA) Advanced license required some math, and my recently-passed Extra license definitely required some basic RLC vector math. No algebraic manipulations though.

author: DimitriP
author_rank: Super Contributor
timestamp: October 17, 2019, 07:50:46 am
content: QuoteYes!Yes

author: BravoV
author_rank: Super Contributor
timestamp: October 17, 2019, 07:59:19 am
content: In the old days, I mean really old, that any computerusersoperators needed to know what a Karnaugh map is.

author: Brumby
author_rank: Unknown
timestamp: October 17, 2019, 09:00:23 am
content: I've just gotta throw this in here...300 is just a rough number - like using22/7for Pi. I'd be happier with something like 299.792458

author: magic
author_rank: Super Contributor
timestamp: October 17, 2019, 09:34:00 am
content: Quote from: soldar on October 17, 2019, 12:27:02 amSpotted the laymanThis is a complete nothingburger for any practical application of mathematics and the word "diversity" appears not even once in the article, not sure where you got that from.Their best chance at achieving any mainstream relevance is a birth of another "new maths" movement in schools which would share the fate of the previous one.

author: bd139
author_rank: Super Contributor
timestamp: October 17, 2019, 10:41:30 am
content: Well I wrote a rather lengthy reply to this, got half way through, got distracted by work and accidentally closed the tab. Ooops.I'll keep this a lot more terse. Edit: I failed at that.I think the cause of this is human apathy and acceptance of incompetence.At school they teach you all the tools to do this and have done here for the last 50 years. I have never seen any evidence of it sticking past school though. For the average person who doesn't need mathematics to survive, literally three episodes of some shitty soap or drama and the space where logarithms lived is replaced by celebrity ass sizes. dy/dx is probably some rapper's name and simultaneous equations are someone writing E=mc^2 twice.When someone has spare time and money and takes on a technical hobby that requires some certificate of competence they are greeted with a wall they have to climb. Rather than seeing it as a challenge it becomes an obstacle and they are so used to just being able to walk around obstacles in life, that they don't bother or blow around the issue with money (typical ham: MOAR POWER! into my shitty antenna rather than working out why it's shitty). This causes declining numbers entering the hobby. And because of that they made it easy. Pass percentages here on our multiple choice tests:Foundation: 73%Intermediate: 60%Advanced: 60%You can get all the mathematics questions wrong and still pass. In fact I suspect that's what happened to a lot of people when I did mine based on the fact that most of them had gone out and bought scientific calculators and were in a right panic because they couldn't use them and didn't know how to rearrange a simple equation from the cheat sheet that comes with the exam paper (yes all the formulas are listed). At best you had to do a simple bit of algebra (rearrange and substitute values in) in the intermediate and advanced papers.This means the average ham here has an idiot test and then a 60% scrape at worst. A lot of people don't get past foundation still. In fact if I look at the local club there are only two advanced members and they really have zero technical expertise as well. These guys train the next generation. I don't go there now because they are quite defensive over their little cult and when someone new comes in with some technical expertise it's a threat. The threat? Well I built a K2 that actually works unlike one of the G0's who fucked it upIt's a race to the bottom. We avoid hard things. We accept incompetence. Or we buy our way around it. In some circles there is even social solidarity about mathematical inability.I don't get humans.

author: CJay
author_rank: Super Contributor
timestamp: October 17, 2019, 11:32:39 am
content: I agree with almost all the comments above to a greater or lesser degree and it frustrates the hell out of me when I see/hear some of the 'wisdom' put about.But...I would also point out that there are *many* hams who never could do maths or the technical bits and never wanted to.A lot of hams have almost zero tech knowledge beyond that required to get their licence and set up a station they bought from a shop so why would they need to know more if they get their kicks from talking to people instead of building gear?Bear in mind a lot of hams use it for local chatter and 'prepping' for emergencies, one of my regular listens is the Alaska Morning net which is available from a local UK 70CM repeater and they're far from technical.It's a broad church.

author: bd139
author_rank: Super Contributor
timestamp: October 17, 2019, 11:48:23 am
content: A very good point.Most of the local 2m users here are like that and fair enough. I couldn’t find any common interest with them (other than growing tomatoes) so I packed it in

author: iMo
author_rank: Super Contributor
timestamp: October 17, 2019, 12:01:12 pm
content: I bet you would have gotten a better answer off the repeater asking them what is "the solution of this equation system":lm = 300 / fmhzlm = fmhzPS: in 2018 I was told (in the local hamradio club) there are people wanting to learn Morse, but not interested in getting the ham radio license.. So the motivation of people differs today

author: xrunner
author_rank: Super Contributor
timestamp: October 17, 2019, 12:06:54 pm
content: Quote from: Brumby on October 17, 2019, 09:00:23 amHello Brumby, yea I know and said at the beginning that the actual number is substituted by 300, that's what the ham community uses. If I put in another number (like the actual longer number LOL), it would look even worse to them and I'd have less a chance of getting anyone to try. Besides the principal of solving the equation wouldn't change and you'd just end up with the √299,792,458Quote from: DimitriP on October 17, 2019, 07:50:46 amI knew it!Quote from: bd139 on October 17, 2019, 10:41:30 amQuote from: CJay on October 17, 2019, 11:32:39 amSee, that's what I assumed, that people had been taught such basic skills even if they didn't particularly like it. I didn't think λ=300/f was in any way so hard to play around with. But, I do have one guy who I asked last week and said he'd try it. I asked the other day if he was still interested in it. He did say he was still thinking about it, so there is still hope. I will give a hint if he gives up and see how it goes from there.Quote from: imo on October 17, 2019, 12:01:12 pmYep - the trick they need to do is realize that those two variables are equal, which is what the description of the problem states "One HF frequency has the same numerical value as it's wavelength". Like I said one guy is still thinking about it ...

author: Brumby
author_rank: Unknown
timestamp: October 17, 2019, 12:59:04 pm
content: Quote from: xrunner on October 17, 2019, 12:06:54 pmSorry. That's what I get by skipping down the problem description and not reading properly.No excuse.

author: Kjelt
author_rank: Super Contributor
timestamp: October 17, 2019, 02:25:39 pm
content: It could well be the noise in your message asking them to solve akjhdsgf ajsdhf98764329587432oriuhqewkjfhqwlkejfhgqoiweuyrqiweuryqoiewuryqwinstead of formulating it clearly and precisely , even better writing it down.Don't forget that a lot of the problems in math are not the math it self but the problem description.Actually it is more language than math what schoolkids get these days which is problematic.Example of 8 yr old:Patricia bought a cake and she cut it in 8 pieces and she asked three friends over. How many pieces of cake does everybody get ?The right answer is it depends how many pieces of cake Patricia is willing to give to her friends, if she wants to share equally or perhaps she gives only one piece each to her friends, eats one her self because she keeps the other four for her brothers and parents.You can see smoke coming out of teachers ears when you bring it like that but often the problem is not unambiguously formulated. Just try again.

author: Rascal
author_rank: Contributor
timestamp: October 17, 2019, 03:00:25 pm
content: A good majority of Hams in the UK use 'plug & play' equipment. No need for math calculations.I think the Ham culture has changed over the years. Back in my Fathers day it was about building and understanding the equipment, experimenting and testing. Today its easy to pass the exam, and then buy a radio, put a large antenna array on your house and off you goPaul

author: ebastler
author_rank: Super Contributor
timestamp: October 17, 2019, 03:54:53 pm
content: Quote from: xrunner on October 16, 2019, 11:36:45 pmMy thoughts would be that this is a meaningless question, unless you clearly specify the units you want used. Try again with the wavelength in miles or feet.Seriously, I would not put this question to a (high school) student. It is a struggle to train them to always consider the units, and take them along in any calculations which they are doing. (Rather than just messing around with dimensionless numbers, and forgetting that they used µs here and Hz there.) Encouraging someone to take the square root of 300 to solve this is encouraging bad practice.

author: Johnboy
author_rank: Regular Contributor
timestamp: October 17, 2019, 03:58:58 pm
content: In my neck of the woods, a mathematical question would be considered unusual among the 2m Technician crowd. That may not be true everywhere, of course, but the majority of discussions I hear on our most-trafficked repeater seem to involve motorcycle maintenance, of all things. It's the equivalent of the "Car Talk" radio show. There is also a sizable amount of "well, my gol-durn knee's swelling up again" prognostication regarding incoming weather.When I took the ARRL amateur exams a few years ago, the majority of the other testers in the room turned out to be drone hobby enthusiasts who were taking the Technician exam because they believed they needed an FCC license for legal drone operation. I don't know whether they actually do or not, but I'm just pointing out that you might have been asking in the wrong circles. I don't feel it's fair to generalize the majority of hams as entirely inept at simple algebra, any more than it would be fair to characterize electricians as "mathematically inferior" to engineers. I'm not flaming anyone, but I don't care for the title of the topic. If you'd asked a group of community college professors to show you that they didn't have to rely on oversimplified formulas to arrive at wavelength in meters, you might have gotten a similar result. I'll vouch for the likelihood that there are many hams whom almost certainly would have had no problem understanding what you were asking them to do.(Although you might need a considerably larger antenna to inquire about it, because those ops tend not to hang around on two meter, or even 40m for that matter. You might even need to send your query with a straight key or bug to establish your own "credentials" in order to get a response from such hams at all. Even a friendly intellectual exercise like this might seem like a set-up, a "trick question" that only people dumbfounded by it would feel obligated to respond to.)I was a little shocked by the concept of metric/imperial/metric conversion in order to make an antenna. It's certainly true that the ARRL handbook (among other similar sources of information) has become almost a parody of itself; to me at least, it does seem to be more geared toward "appliance operators" rather than experimenters/makers in its current incarnation than, say, the one on my shelf (from 1986, even). I would be thrilled to hear more discussions of the technical aspects of RF on the bands on a regular basis, but it is much rarer than it used to be, for sure.

author: xrunner
author_rank: Super Contributor
timestamp: October 17, 2019, 04:46:44 pm
content: Quote from: Johnboy on October 17, 2019, 03:58:58 pmI understand and I changed the original title to a better one, which is as true as I can get. I have not asked anyone other than hams and it was just a few.Thank you.

author: Johnboy
author_rank: Regular Contributor
timestamp: October 17, 2019, 05:04:32 pm
content: Quote from: xrunner on October 17, 2019, 04:46:44 pmI wasn't being snarky, xrunner; thank you for not taking offense. I myself had never considered your question before, and I thought it's just the type of riddle that ought to be included on the amateur exams. I think the US exams seem to be more focused on making sure the hams "know their place" and don't interfere with signals outside of their bandwidths, rather than on showing that they understand the science behind the hobby.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 18, 2019, 02:23:21 am
content: Quote from: Brumby on October 17, 2019, 09:00:23 amLife is a "rough number"-----I'm quite happy with 0.0692% accuracy, as I'm quite sure I couldn't measure wavelength to that degree of accuracy, anyway!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 18, 2019, 02:55:36 am
content: Quote from: ebastler on October 17, 2019, 03:54:53 pmI think this is the root of the problem, we have all had it hammered into us that "numerical values without units are meaningless!"This makes it difficult to re-organise our brains to work with just the unitless values.We cannot, in conscience, say, "frequency =wavelength", as it is like saying "Cat=building", so we must have the verbose explanation.In the end, it is a mathematical curiosity, of no more importance than the fact that, in Ohms Law, the numerical value of R, I, & V are equal when they all=1.Pretty much----"So what?"

author: fourfathom
author_rank: Super Contributor
timestamp: October 18, 2019, 05:44:41 am
content: Quote from: vk6zgo on October 18, 2019, 02:55:36 amSo what? So what??? "1 V / 1 Ohm = 1 A" is a beautiful thing. So is "1 V * 1 A = 1 W" I refuse to let you dismiss these identities as a mere curiosity.

author: hamster_nz
author_rank: Super Contributor
timestamp: October 18, 2019, 06:52:26 am
content: Quote from: fourfathom on October 18, 2019, 05:44:41 am1 is pretty straight up and down, and I have nothing against 0, but what about pi, e and i?Those numbers have a real (and even imaginary) significance - maybe even a little bit of special magic about them.

author: ebastler
author_rank: Super Contributor
timestamp: October 18, 2019, 08:03:12 am
content: Quote from: fourfathom on October 18, 2019, 05:44:41 amAnd if you divide one by 5, the result is 1/5.Hey, look -- the same number in the denominator which we just divided by! Amazing!!This stuff doesn't even qualify as a "curiosity" in my book.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: October 18, 2019, 02:48:16 pm
content: Quote from: xrunner on October 16, 2019, 11:36:45 pmTechnical people? I think most of these guys take a one-day cram session to memorize just enough to pass the test, and then they promptly forget it.

author: fourfathom
author_rank: Super Contributor
timestamp: October 18, 2019, 03:59:25 pm
content: Quote from: ebastler on October 18, 2019, 08:03:12 amIt's not the numbers, it's the relationship -- one of the most fundamental relationships in electronics. I will admit that plugging "1" into the equations is not strictly necessary to appreciate the beauty of Ohm's Law, but it does seem to make the example more concrete.It's an engineering aesthetics thing, perhaps you and I will never agree.

author: james_s
author_rank: Super Contributor
timestamp: October 18, 2019, 04:46:34 pm
content: I've never been a math guy, I know that's odd for someone in engineering but I've just always struggled with the math part. I can learn how to solve the equations I need and the basic stuff like Ohms law I know like the back of my hand, but I've never really grasped or been interested in the abstract mathematics behind it all, it's just not how my brain works. I'm a very visual thinker, I can easily visualize complex mechanical systems in my head and see how everything fits together. I'm good at applied math, when I can see the math "doing something" and relate it to the physical world I can usually pick it up no problem. When it's just manipulating numbers for the sake of manipulating numbers though my eyes glaze over.

author: Bicurico
author_rank: Super Contributor
timestamp: October 18, 2019, 06:49:30 pm
content: I have not understood what the original poster wants to be calculated.While I do believe that there may be HAMs unable to solve mathematical questions, in this case it seems that the question is not clear.Regards,Vitor

author: ebastler
author_rank: Super Contributor
timestamp: October 18, 2019, 07:50:39 pm
content: Quote from: fourfathom on October 18, 2019, 03:59:25 pmSorry, but now you are muddying the waters. It was exactly the fixation onnumbers, ridding them of units and physical meaning, which I was questioning in the first place.QuoteTo the extent that "1/1 = 1" means engineering aesthetics to you, indeed, I'm afraid we won't agree.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: October 18, 2019, 08:30:45 pm
content: Quote from: james_s on October 18, 2019, 04:46:34 pmOne of the things that's wrong with physics these days (IMO) is that too many physicists equate "beautiful" math with reality--theories that have no experimental proof (and no prospects of any in the future), but "it must be right" because the math is pretty.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 18, 2019, 08:32:48 pm
content: Like String theory?

author: worsthorse
author_rank: Super Contributor
timestamp: October 18, 2019, 08:56:10 pm
content: Quote from: bd139 on October 17, 2019, 10:41:30 am/beginIn the US, these points are in the preamble of Part 97, the regs that set up the amateur radio service. They lay out why we get to use the RF spectrum:Continuation and extension of the amateur's proven ability to contribute to the advancement of the radio art.Improvement of the amateur service through rules which provide for advancing skills in both the communication and technical phases of the art.Expansion of the existing reservoir within the amateur radio service of trained operators, technicians, and electronics experts.That is, we are allowed to use the RF spectrum because doing so makes us more technically competent. For a long time, this was actually true of most hams.But it has been decades since organizations like the ARRL promoted technical skill over, say, contesting or collecting badges. You don't have to look any further than the current book list or QST magazine to see that. I think this is, in part, because the ARRL has become a marketing channel for companies selling high end gear but whatever the reason, the result is a community of radio amateurs who mostly don'tadvance the artin any sense of the phrase.That is not to say that every ham before 1999 was an RF or analog engineer. The vast majority weren't. But most of them learned the hobby through building and fixing gear and by studying technically oriented books likeA Course in Radio Fundamentals. Today, the vast majority of hams in my part of the world attend a one day cram course to memorize answers to the test, get a technician license, and never think about the technical aspects of radio again.While it is certainly human nature to find the easiest, lowest energy way to attain some goal (I am a prepper. I need a powerful radio. I can get a ham radio license in one day for less than fifty bucks. Done.) it is also human nature to be curious about how things work. (How does this work? What happens if I change that? How can I make it better?) Unfortunately, our culture rewards efficient goal attainment (get your DXCC in five months with FT8 vs. twenty years with CW) over understanding how shit works. And while this is the way things are, understanding RF or maths or geology or astronomy will not be of much interest to most folks./end

author: janoc
author_rank: Super Contributor
timestamp: October 18, 2019, 09:55:11 pm
content: Guys, don't diss HAMs here.I used to teach at a fairly decent tech university and I had students totally dumbfounded with elementary school math on more than one occasion. E.g. once I wrote fractions on the blackboard as a result of some calculation (didn't have a calculator on hand and the numerical result didn't really matter anyway), I drew blank stares from the class and a complaint that "The result is wrong because it is not what his calculator is showing!"Colleague that taught also at a local gymnasium (type of high school, not a gym!) explained me later that they have never seen fractions because apparently some smart cookie at the education ministry has decided some time ago that today everyone has a calculator and fractions were dropped from the curriculum!Another time I had to explain how to do calculations with negative numbers (not kidding!). Or complex numbers. Or basic algebra, like equation solving. Or ...Even had an engineering master student (4th year!) be totally stumped with having to multiply two matrices during an exam - he has never learned how to do this because "I have never needed it." (?!) (he failed that exam)And those were all engineering students, with at least the mandatory first year of algebra and calculus under their belts when I got them, studying stuff like computer science and electrical engineering!So don't poke fun at mostly elderly guys that had to do some algebra sometime in the high school the last time, some 30-40 years ago. Lack of basic math skills is a general population problem, HAMs are not special here by any measure.

author: fourfathom
author_rank: Super Contributor
timestamp: October 19, 2019, 02:36:09 am
content: Quote from: ebastler on October 18, 2019, 07:50:39 pmI agree with you that "1/1 = 1" is neither interesting nor beautiful. I'm sure that we can find something more interesting to argue about somewhere down the road.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 19, 2019, 02:16:38 pm
content: Remember that video a few years ago where some fresh MIT grads were being asking a simple question about a light bulb and battery?

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 20, 2019, 01:39:58 am
content: You are calling people out for not making an intuitive leap you yourself did not even describe.λ = c/f ⇔ λ·f=cis the easy part, and a lot of people will get that far. The trick is understanding that the next step isλ = x·1 andf = x·1,000,000 and substituting them to the original equation:x·1  · x·1,000,000  = 299,792,458 [m/s]which simplifies tox2= 299,792,458 [m/s] / (1  · 1000000 )and tox2= 299.792458yielding the solution,±x = √299.792458 ≅ 17.314516Substituting back to the original variables, only positive values make physical sense, soλ ≅ 17.315 f ≅ 17.315 Unless you show the entire sequence of operations needed to get to the result, you're skipping things, and not presenting the problem and solution realistically; you are skipping major steps that you might have found intuitive. Mathematicians do this extremely often; even in peer-reviewed articles, the interesting bit,howto find a numerical answer, is very often completely ignored and skipped. That may work for mathematicians, but it does not work for us who just use math as a tool.Do not be a mathematician.So, in a way, it is a similar trick question as asking how much is eπ-π. When you calculate that, you'll recalculate it again, because you'll think you calculated it wrong. You didn't, it is just a numerical coincidence.

author: fourfathom
author_rank: Super Contributor
timestamp: October 20, 2019, 02:07:35 am
content: λ·f=c (meters, megahertz, 300)Given that λ=f, F*F=c, f2=c, f=√csince c=300, f=λ ≅ 17.32MHz

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 20, 2019, 03:29:35 am
content: Quote from: fourfathom on October 20, 2019, 02:07:35 amThat makes absolutely no sense whatsoever.It only makes sense if you think physical quantities can be represented by dimensionless numbers. People should not think that way, because it leads to errors (both numerical and logical).Dimensional analysisis your friend, and a very important tool in understanding things.

author: fourfathom
author_rank: Super Contributor
timestamp: October 20, 2019, 06:57:56 am
content: Quote from: Nominal Animal on October 20, 2019, 03:29:35 amOK, how about this:λ·f=c (meters, megahertz, 300)Let λ = kLet f = kk * k = 300k = √300k = ≅ 17.32f = ≅ 17.32MHz, λ ≅ 17.32meters

author: RoGeorge
author_rank: Super Contributor
timestamp: October 20, 2019, 07:59:59 am
content: About measuring units, it's crucial to keep them attached to the numbers.1*1=1 is very, very different from 1A*1=1V or from 1A*1V=1W, because each equality describes something else.Also, 1 centimeter is not the same as 1 meter or 1 inchhttps://www.simscale.com/blog/2017/12/nasa-mars-climate-orbiter-metric/No way to neglect the physical units in engineering, not even by mistake.Quote from: xrunner on October 16, 2019, 11:36:45 pmFirst, why would this value be interesting? I don't get it.Second, the sentence is misleading, because usually "same numerical value for both it's frequency and it's wavelength" does not imply MHz and meters, but Hz and m.

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2019, 11:32:56 am
content: Quote from: janoc on October 18, 2019, 09:55:11 pmToday, the most talented EE students use Excel in order to solve such math problems, like - when and how far from town B or A the two cars meet themselves

author: ebastler
author_rank: Super Contributor
timestamp: October 20, 2019, 03:51:39 pm
content: Quote from: fourfathom on October 20, 2019, 06:57:56 amOuch.I think a cleaner notation for the starting point would be e.g.λ/m · f/MHz = c/(106m/s).That gives you dimensionless quantities λ, f and c to play with.

author: james_s
author_rank: Super Contributor
timestamp: October 22, 2019, 03:52:13 pm
content: There was no other way, if you wanted to communicate with people all over the world and weren't rich you had to build equipment, modify surplus gear and understand the technical details. Now there are other options, and given the fact that ham in general has so much less draw, it needs all the options it can get in order to keep the hobby alive. Must have been very exciting back in the day to make a contact in a foreign country, it's still cool but I interact with people all over the world right here on the forum. I can even use my phone to make a voip call to my friend in the uk for free. I can't justify spending a bunch of money on radio gear.