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Author Topic: back your post with mathematics  (Read 2067 times)
WX7G
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« Reply #15 on: January 12, 2010, 06:28:53 AM »

K0OD,

I think where you have an issue is S-meters more than S-units. I agree that ham rigs have notoriously inaccurate S-meters. We could also say that ham rigs have notoriously inaccurate decibel meters.

When I make the statement "that costs 1/2 S-unit" one will calculate in their head that that is 3 dB. When I make the statement "that costs 3 dB" one will calculate in the head that that is 1/2 S-unit. There is no getting away from the S-unit and decibel conversion in amateur radio.

We need an electrical unit to describe the power ratio between two signals or two treatments of a system. Decibels are univerally used, with Nepers used by physicists, and S-units by amateur radio operators. What is a Neper? It is like the Bel but based on the natural logarithm rather than the base 10 logarithm.

S-meters have been around since the 1930's. I don't know when the 6 dB per S-unit definition was first offered. I can find no documentation - just heresay - that James Millen proposed it.

In any event, being that the S-unit is an amateur radio unit of power measurement it seems appropriate that the IARU (International Amateur Radio Union) officially defined the S-unit.

Interesting tidbit. The American Wire Gage (AWG) is logarithmic with wire area proportional to 10LOG(N1/N2). Wire sizes are like decibels. When we say the wire size is #16 we can also say that the wire is 6 dB below (or -6 dB) #10 wire. #16 wire is 1 S-unit below #10 wire.
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WG7X
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« Reply #16 on: January 12, 2010, 07:23:06 AM »

Amateur radio is not comprised solely of electrical engineers.

Amateur radio is a small slice of the the overall community and as such, represents us all, not just the scientist or engineer.

At one time, certainly most (some) of the ham population came from the technical ranks. Back when radio itself was leading edge technology.

Radio has not been leading edge for many decades. Emphasizing the technical (mathematical) side of the service is doing us a disservice.

Personally, I admit... I'm not a mathematician nor an engineer.

Does that make me less of a ham?

To some I guess it does... Oh Well.. Life still goes on regardless.

The best thing, I've found is simply not to get into these endless internet arguments. That way people still have to guess whether I'm competent or not based simply on my accomplishments.

73 from a "Non-mathematician but still a ham"

Gary WG7X
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K9IUQ
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Posts: 1775




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« Reply #17 on: January 12, 2010, 08:24:31 AM »

Math gives me a headache. I do not need to see it in a post. I never believe much here on eham anyway. Putting  math in a post on eham is mostly for the poster's ego......

Stan K9IUQ

Give me something I can understand like "If I can hear em I can work em.  :>
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K5END
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« Reply #18 on: January 12, 2010, 08:25:39 AM »


Radio has not been leading edge for many decades. Emphasizing the technical (mathematical) side of the service is doing us a disservice.


Not sure I agree with that.

In the commerical world there is a huge amount of development and challenges for the so-called "wireless" telecommunications.

When the day comes that your cell phone, satellite TV or other "wireless" devices work just fine all the time, every time, no matter what, in all kinds of weather, then perhaps we will have exhausted the frontier of radio.



"Technical" and "mathematical" are not the same thing, but they are intertwined. When people encounter problems learning or applying technical material, it is often because they have approached it from a detailed perspective instead of looking at it with an "understanding."

But instead, they try to use memorized "formulas" such as "1005/f" or "246/f" as if they are doing a tax return.  This is the wrong approach, in my opinion.

The better way is to approach it with understanding of the fundamentals, which in many cases is to consider the basic physics.

Ooooohhhh, scary word, "physics." That is another misconception. Physics is by nature, "simple." That is one goal of physics: to make a simpler expression to explain things. (That doesn't mean it is always easy, I concede.)

But I do like the simplicity of "if I can hear 'em, I can work 'em." That's not far off from the reciprocity theorem. Smiley
« Last Edit: January 12, 2010, 08:33:34 AM by K5END » Logged
K0OD
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« Reply #19 on: January 12, 2010, 08:31:34 AM »

That the IARU would bother to define an S-Unit is certainly puzzling. Why would they do that? Do any of their regulations hinge on S-units?

Why stop at the "S" in RST? The IARU could promulgate modern lab standards for "R" and "T" too. (imagine a Flex 10000 coming out in 5 years with the worlds first RST-meter. LOL!). The T part might be pretty easy to do nowadays.

The RST system doesn't date to ham radio's earliest days. RSTs began appearing on QSL cards around 1930.

It's time to ditch the S-unit. With my new Flex, I've given out a few dBM reports, some stated in relation to ambient band noise.
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N8EKT
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Posts: 371




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« Reply #20 on: January 12, 2010, 09:25:47 AM »

I DO believe that hams in general have become more appliance operators than inventors and developers.
How many hams do you know that still BUILD their own test equipment or transceivers?
I either never had the money to purchase test equipment
when I got started or had to build my own test equipment because nobody had invented or produced one yet that did what I needed it to do.
NECESSITY is truly the mother of invention.
But now that I can afford it, I have also become lazy, and simply purchase the test equipment I need.
The ham community in general is still a great technical
resource that has HUGE potential in the next quantum leap forward in technology.
Silent key John Kanzius K3TUP is a prime example.
His revolutionary RF cancer treatment may someday save the lives of millions.
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K9IUQ
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« Reply #21 on: January 12, 2010, 09:44:09 AM »

"It's time to ditch the S-unit. With my new Flex, I've given out a few dBM reports"

Aint gonna happen. Even Newbies know what a S-unit is. Gve a dbm report and most hams are going scratch their heads and say huh?

Stan K9IUQ
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N3OX
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« Reply #22 on: January 12, 2010, 11:14:28 AM »

When I make the statement "that costs 1/2 S-unit" one will calculate in their head that that is 3 dB. When I make the statement "that costs 3 dB" one will calculate in the head that that is 1/2 S-unit. There is no getting away from the S-unit and decibel conversion in amateur radio.

But we should try to kill it.  There is never a point in using S-units in technical discussion, because many hams think one S-unit is one division on their radio's scale, i.e., something they can measure simply.

"I measured my Moxon Rectangle and it had four S-units F/B ratio" in NO WAY means that antenna has 24dB F/B.  It means that on whatever that person's S-meter, it had 4 ticks difference.  On my FT-857's S-meter, that could be pretty crummy or pretty good depending on what part of the scale you were on.  Nowhere would it actually be 24dB.

I think we should always use dB on the off chance that we can encourage people's first thought to be "hmm, how do I measure dB?"    They may still try to apply a "four S-meter ticks = 24dB" rule, but at least we didn't SAY anything about S-units.

Not very many radios are any good at consistently measuring 6dB S-units.  But every radio appears to measure S-units.  If we knew that 73% of inch-ruled tape measures were off by up to 3 inches in what they called an inch, with the remaining ones accurately marked off to 2.54cm per inch, but we also knew that all centimeter tape measures were fine, the message "don't measure things in inches" is, IMO, justified.

I think it's important that people know that they don't have a good measuring stick unless they do some extra work to figure out what their S-meter is actually telling them.  Discussing S-units instead of dB, in my opinion, makes it more likely that people will trust their meters, something they shouldn't do without independent calibration.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K5END
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« Reply #23 on: January 12, 2010, 11:22:00 AM »

The S unit is dead. Long live the deci-Bel.
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K0OD
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« Reply #24 on: January 12, 2010, 11:47:46 AM »

Dan, having a Flex has renewed by respect of the lowly dB. I once mentioned in a post here that I believed that even one dB could make a difference in a station's contest score. I based that opinion on the huge score differences usually found between LP and HP CQWW scores.

I've often heard radio gurus roughly define a dB as the tiniest signal difference that a human can detect... ALMOST nothing, a "human hair's width" of audio. 3dB, not much either, is often considered the smallest difference worth worrying about outside a lab.

But with my Flex I can clearly detect a single dB change.  (and I'm a geezer who can't tell whether I'm watching TV in HD or low def... my wife kids me about that)

I can pretty well adjust my antenna tuner just by listening to band noise. The noise difference between a 3:1 SWR and <1.5:1 is probably less than a dB.
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WX7G
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« Reply #25 on: January 12, 2010, 12:29:48 PM »

N3OX and K0OD you've convinced me to stop using the S-unit here. I'll use decibels.

As to decibels I am amazed that I have not been hit with the "do you mean dB volts or dB watts" question. I occasionally encounter this in industry and then have to explain that a dB is a dB is a dB; that a dB is a measure of the ratio of two powers. Next comes the explanation of how 20LOG(V1/V2) comes from 10LOG(P1/P2).
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N2EY
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« Reply #26 on: January 12, 2010, 01:18:12 PM »

N8EKT asks: "How many hams do you know that still BUILD their own test equipment or transceivers?"

(raises hand)

I do!

73 de Jim, N2EY
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KC0SHZ
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Posts: 372




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« Reply #27 on: January 12, 2010, 01:29:43 PM »

At the recent ARRL Kids Day, my 13 year old niece got a first hand chance to learn about the Ionosphere and about the effect of cold weather in the lower atmosphere on propagation.  She made 3 contacts to the East coast and none from the West Coast.  

We got to talk about the atmosphere, and how radio waves moved.

We got to briefly touch on Einstein's theory of general relativity.

All in a brief afternoon of ham radio fun.  

Whether I am an "appliance operator" or a "REAL HAM RADIO OPERATOR (tm)", I would call that a productive afternoon.

When she goes to school and some science teacher asks for an example of relativity, she can cite what she has experienced with her times on the radio.
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WG7X
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« Reply #28 on: January 12, 2010, 02:30:30 PM »

K5END,

Since you quoted my reply, I will reply again to expand a bit.

Amateur radio is now and always been a technical service. If it was not then we would not exist.

My point was simply this: to be an Amateur radio operator, one does not necessarily have to be an electrical engineer.

In fact, possibly ham radio might look more to the "softer sciences" if we want to include more people in the hobby.

A hard focus on the science of radio is not necessary now. Yes, folks should have an interest in and a basic understanding to the technical aspects, but no to the level that the other thread was alluding to.

73 Gary
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N3OX
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« Reply #29 on: January 12, 2010, 07:06:24 PM »

Gary,  you're quite right that hams don't have to be technical.  And I also think we need to be respectful of good non-mathematical insights from non-mathy folks.  There are lots of topics on which that is straightforward.

However, I think that there is something of an issue in this hobby of authoritative sounding but totally wrong ideas coming from people who maybe don't have the math and physical intuition to recognize the errors they're making.  Some of the pontification I hear on the low bands about antennas is, I think, harmful nonsense.  Some of these people are so ready to take new hams under their wing and teach them a whole book worth of wrong electromagnetic ideas....  

Sometimes they're guilty merely of marginally useful oversimplification and generalization, but some of it is basically fairy tales; ideas that are totally incompatible with actual physics. Does this necessarily ruin the hobby for non-technical folks?  Maybe not, but I think it does a great disservice to those who want to learn the right things.  And I think it injects a significant element of luck into whether or not the non-technical people can find good technical advice to set up their stations.

I don't think everyone needs to focus on hard science.  That said, I really hate to see how potential amateur scientists and amateur technical people first have to un-learn the things they learned from their local blustery guru before they can make solid technical progress.   If we can foster an environment on eHam where we spend time trying to quantitatively support our positions where quantitative considerations are warranted, we'll be better off.  It slows down advice giving, and it allows the advice givers to LEARN something too.  I've learned a lot by nearly hitting "Post" and then going back and saying... "waaaaaaait a minute, do I *know* this is true, or is it just my OPINION that I think is physical fact?"  45 minutes later, I might not even have a post anymore, but I do have a better understanding, or at least a knowledge of what I don't yet know about that topic.

I've thought a lot about this in regard to certain antenna topics.  There are certain aspects of short antennas that are real traps for qualitative discussion.  There tends to be a "full size or nothin" crowd and a crowd that doesn't much care how short it is, they know it "works."  The "full size or nothin" crowd seems to think that ANY shortening causes noticeable loss and the "it works" crowd doesn't recognize the steepness of the performance dropoff at the "really short" end and the fundamental tendency of super-short antennas to act as feedline exciters more than they do antennas.

You get the "it works" crowd insisting that their 30 inch 40m antenna (mounted, of course, atop a grounded 33 foot pole, no balun included) works just as well as their weirdo off center fed antenna, so it MUST work as well for anyone who tries it, and further, it's negligibly different from a full size dipole. Then you get the "full size" crowd railing against really excellent quarter-wavelength-total-length dipole designs with big capacitance hats and reasonable amounts of loading inductance...

Neither of those positions are really supportable, yet both are very popular.  Those two particular groups like to argue with each other, and ultimately all they manage to do is greatly decrease the forum signal-to-noise ratio.  Then when it comes down to it, the apartment dweller who listens to the "it works" crowd and buys the 30 inch antenna and feeds it with three feet of feedline has just installed a really miserable antenna system.  And the limited-space PSK enthusiast who one who swears off HF because of the "full-size" advice?  Maybe that person could have built an 85% efficient antenna with 20kHz 2:1 SWR bandwidth in the space available.  That's all the bandwidth they'd ever need, and more.  

In the end, to attract more non-technical people and to maximize their chances of ham radio success, we need to have good plain-English advice and answers to their technical questions.  *Sometimes* that means glossing over some details.  But, in my opinion, it's important for us to work toward advice and answers that are  understandable by relatively non-technical folks but where applicable, are as scrupulously quantitatively correct as we can make them.

73
Dan
« Last Edit: January 12, 2010, 07:50:08 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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