Useful tool when designing an antenna

Golly! a calculator to convert frequency to wavelength...

What a waste of a powerful computer connected to an immense database called the internet.

John.

So What !!

Now, now. Play nice children.

Electroman, the wannabes need their space on the internet also.

So what, if you can do the same thing on a hand held calculator.

So what, if you can create a whole table of conversions with a simple Excel spreadsheet.

So what, if it is unlikely that anyone actually needing a crutch like that could do anything creative with the information!

So what, if the simple formula for wavelength in meters is 300 divided by frequency in MHz. and meters are easily converted to inches by moving the decimal point three places for millimeters then dividing by exactly 25.4 (not an approximation!) and then by 12 if you want it in feet.

So what, if it would be a shame to have to go to a website every time you want to calculate a wavelength for a given frequency.

So What!!

Hi STL Engineer. My pocket calculator converts metric to imperial, or vice-versa, measurements at the push of a button. If I punch in 10mm the answer comes up= 0.394", likewise if I punch in 12" the answer= 0.3048mm exactly. Spencer.

Spencer,

Holy Cow! Since when is 12 inches smaller than a millimeter? (Is that what you told her last night? ) Better get that calculator fixed. My brain hurts! 12 inches is equal to 304.8 mm, exactly.

And regarding the other conversion of 10 mm to .394 inches, your calculator may do that, and you may think it is exact, because there are no digits shown beyond three or four places, but it truly is a rounded off approximation, and not very exact at that since engineers commonly use .0001 inch, ten-thousandths, or "tenths" (of a thousandths) or less. An analog micrometer will take a measurement that low, and profilometers will go even lower, to micro-inches (.000 001 inch) in some cases when measuring surface roughness (height of surface irregularities). 10mm converted to inches may easily be taken out several more places to say, .393701 (my PC calculator does it to 0.3937007874015748031496062992126)

Just like I memorized Pi to more than 3.14 (3.14159 if memory serves me), it may not be necessary in most cases, but if you keep more precision, you can always round off later. If your calculator was correct, and 10mm was exactly 0.394 inches, the conversion factor would be 25.380710659898477157360406091371, well, at least to 30 decimal places!

By international agreement, the inch is defined to be, EXACTLY 25.400000000000000000000000000000mm. I could add more zeroes but I think you get the point.

You seem to have a calculator displaying an additional m. Put some paint over it.

I repeat so what ! !

thanks mhoward -- I will find this useful, as I am 64 yrs old and still find things useful, as I really don't know everything YET.

ietech,

I would have thought at age 64 you would have learned it's not knowing everything that counts, but knowing how to use what you know effectively and how to find out what you don't know!

Oh, yeah, and being able to accept correction for what you thought you knew, but really didn't!

And, hey, if you find this "tool" useful, that's great. Just don't be surprised if you find that most here on this forum do not consider it so.

By the way, what is an "ietech" anyway?

You're just really full of yourself aren't ya --

By the way, what is an "ietech" anyway?

Sorry i forgot to answer your question -- but of course I really shouldn't have to answer since you have all the answers already. You figure it out -- rude one.

"Sorry i forgot to answer your question -- but of course I really shouldn't have to answer since you have all the answers already."

I never claimed to have all the answers, quite the opposite. Please re-read my post #5 with an open mind. Maybe you will get something out of it.

"You figure it out -- rude one."

"You're just really full of yourself aren't ya --"

Oh, I'm the rude one? I am not the one calling names and casting aspersions . My earlier post #3 was simply rising to the challenge of Guest #2 who said, "So what?". I only intended to show that there were simple ways to do the same thing without using the internet as a crutch.

And my question to you was a legitimate one. I am always interested in the story behind some of the more interesting screen names. If you chose to make it and my other post some kind of personal attack, well then, that's just your problem, not mine.

Very nice response you made below and the rest of this post is basic middle school stuff.

Holy Cow! Since when is 12 inches smaller than a millimeter? (Is that what you told her last night? ) very nice --- bah

Better get that calculator fixed. My brain hurts! 12 inches is equal to 304.8 mm, exactly.

From another post So what, if it is unlikely that anyone actually needing a crutch like that could do anything creative with the information!

And, hey, if you find this "tool" useful, that's great. Just don't be surprised if you find that most here on this forum do not consider it so.

How do you know that MOST folks on this forum would not consider this tool useful, have you asked them all and gotten a valid percentage either way?

Electroman, the wannabes need their space on the internet also.

Your responses to a new member were un-necessary and highly negative. His first contribution was not received well -- possibly he was testing the water and being friendly. Responses could have been positive and encouraging.

I reviewed your bio -- quite nice -- you should be proud! But being proud is very different that being prideful and arrogant.

If you have no use for a person's contribution or comments why do you bother to respond. It seems a person with vast knowledge, such as youself, would have better things to do. Why waste your valuable time being degrading and unaccepting of things that some other folks might find vaulable. There are some social values that are necessary to be a good eng. or a good person for that matter. Unfortunately they aren't a requirement for an engineering degree.

John, he's picking on me!

Is he STL??

I read that post and wasn't sure who he was trying to refer to... I thought he was 'having a pop' at both of us!!

He starts by talking about the posts below and not the one he is answering - So I think its probably best to just smile and nod at him!!

ietech certainly doesn't appear to be as old as he stated, maybe he calculated his age using the internet and rounded it up by 50 years?!!

John

Well, ALL of the quotes "ietech" put in italics, bold, and underlined (talk about overkill!) were from my posts! So I had to assume he was picking on me alone!

Frankly, I don't get all this talk about being "nice" and "not scaring away new members". Is this a club for babies who can't take a little criticism? I sure have received my share of it! Personally, I would hope that if someone felt their position was defensible, they would come back with a logical counter-argument, and not just cry like a baby, "waah!, waah! you hurt my feelings!" or start calling names (Rude One, for example!).

Man, if this is a club for engineers who feel that way, they better not ever work in the real world, where people who couldn't even engineer their way out of a paper bag take pot shots at every good idea you ever have, just to puff themselves up. Engineers need to have a thick skin and either accept correction when they realize their errors or be able to defend their positions with logic and evidence, not whining.

I will now step down off my soapbox!

ietech, I'm surprised at your response to STL especially as you should know better at your age.

My original post #1 decrying the use of a computer connected to the internet to do a very basic calculation was an attempt to start a discussion about how we take the power of the computers we use and of the immense knowledge base of the internet and then forget to do simple mental arithmetic in our heads.

It looks like most people seem to have thought I was being rude to the opening poster for which I apologise to him/her.

Sometimes its very difficult to remember that this is an international forum and, in my case, not just based in the UK where a touch of sarcasm would be noted in my first post and smiled at.

With international posters any form of wording of a post can very easily be mis-read and mis-interpreted... This is why I read other people's posts with a casual air.

Perhaps you should try the same?

John.

John,

Its not just a UK/US thing. I got you, and I am here in the heartland of the USA. Perhaps its because I am a bit of an Anglophile myself, I don't know. Certainly a certain segment of the US population finds British humor off-putting. However, you really can't even put one label on British humor anyway. Many Americans loved Monty Python, but hated Benny Hill, and vice versa. Or loved both. Or hated both. And that's just one example.

Yes, I certainly never expected to provoke that sort of response. It did seem a bit much.

I especially liked the "Guest" who said "So What !!" and then "I repeat so what ! !"

How very erudite. (Caution: Sarcasm at Work)

Cheers, John!

Yes, perhaps I should end my posts with....

John < /sarcasm >

Actually the formula is too basic... it will produce an antenna that is 5 to 10 percent too long every time.

The quick formula is

Wavelength == (300 / Frequency) * Velocity Factor == meters

The magic number 300 represents the wavelenth of a 1 mhz signal travelling at the speed of light.

300 == 300,000,000 meters per second / 1,000,000 cycles per second.

However, only in a vacuum dos a radio wave move at the speed of light. Everywhere else it is slowed down somewhat by the medium it traverses. Changing it's velocity affects it's wavelength.

For air VF == .997 , Copper == .95, Aluminum ==.94, RG8 coax == .66

Now, anyone who's ever used an SWR meter knows you want to start off deliberately too long and trim your creations for the best "match" to your transmitter. Ignoring the VF is one way to accomplish this... except when you really need to get it right the first time, such as when you're cutting Coax tuning stubs...

Join the ARRL

Buy The Antenna Book

Buy The ARRL R.A. Handbook

or the equivalent wherever you are located.

There is a whole world of neat stuff to explore in Amateur Radio!

mhoward - thanks for taking the time to share the information with everyone. Obviously, some people more experienced in antenna design find the information redundant. However, those of us not so experienced (to whom, I assume, you addressed your post) appreciate it. Now, if those who have mastered all the disciplines in in engineering could divert their interest towards mastering common courtesy, just think of the potential. Thanks Again For The Info. I happen to be working on an antenna as we speak. Tim. Lousy engineer. Nice guy.

Welcome to CR4 -- a new guy on the block is good because new points of view are very valuable. Don't judge the whole forum by responses that are less than civil -- like some of those in this thread -- there are a few folks here that are like that -- just ignore them. And keep on posting most folks here have an open mind and if they are not interested in your posting they will simply not respond. Then there are others who try to insult or degrade to make themselves feel taller. These are few and far between.

I am not in radio but have some ham friends spending a lot of time figuring out antennas.

Most of them know the optimum lengths by hart.

From what I have seen is after watching their efforts to get a antenna on a vehicle right for 1/2 a day. What the are looking for is the sweet spot where the antenna perform acceptably well on a range of frequencies.

Hi mhoward,

Welcome to CR4, I hope you get out of being involved in CR4 as I do. Don't worry too much about the negative responses, the majority of CR4 members are only too willing to help and learn from what others post. Whilst it is true that most engineers will know the relationship between frequency and wavelength the link you supplied has itself go further links to other items that can be of help.

Don't be put off and restrict your queries because you think it may be a stupid question. If you are feeling self conscious you can ask any of the CR4 members a question confidentially using the CR4 internal message system. Just click on a members name in any thread and follow the "Send xxx a message" link Alternatively, by following this link to the send MASU a message page which will allow you to send me a confidential message.

Ooops, I didn't expect to cause so much trouble... . I know it's a simple calculation but... why use a calculator and think about unit conversion, if we spend XX% of our time in front of the computer and it can help us? ;)

Thank you very much for your support.

If things didn't get stirred up every now and then this could turn into a terribly boring site and nobody would bother to participate. Actually the discussions then to meander all over the place and split into multiple sub threads that have little to do with the original post. Come to think of it that's pretty much what happens when you add copious quantities of beer to a room full of engineers so I guess CR4 is a pretty good representation of the real world.

mhoward,

Nothing against you personally, or the person who put up that website, but it just seems to me, and apparently a few others, that it is just overkill (for Engineers anyway). Why not put up an Ohm's Law calculator (oh, I bet there probably are a few), or one that does Force = Mass X Acceleration, or Metric/Inch conversion, etc., etc., etc.

Yes, they are out there, but does any Engineer (and CR4 calls itself "The Engineer's Place for News and Discussion") worth his salt really need stuff like that? That is the point we are trying to make.

But then I read the post from someone who relies on his calculator to give him "exact" unit conversions, when it apparently rounds off to three decimal places, and I have to wonder! I am still wondering how 12 inches can be less than one millimeter, all kidding aside.

That is why any calculation I do I always carry the units along and perform the same math on the units as I do on the values. And do a sanity check by stepping back and saying, what do those numbers really mean? What do they represent? Does this result make sense? I "know" that a quarter-wave antenna on 2-meters is around 20 inches (about 1/2 meter) long, so the calculated wavelength result for 146 MHz being 2.0548 meters make sense. Yes, as someone else pointed out, there are other factors when designing an antenna, so "cut long and trim to resonance" is good advice.

If you feel the need to use such a crutch, be my guest. I am glad it works for you. Just don't expect everyone here to be as enthusiastic about your "find".

STL said: " If you feel the need to use such a crutch, be my guest. I am glad it works for you. Just don't expect everyone here to be as enthusiastic about your "find"".

STL said: "And, hey, if you find this "tool" useful, that's great. Just don't be surprised if you find that most here on this forum do not consider it so".

Some responses from CR4 members

Are "On LINE" calculators useful to you??

Hoo boy! Where do I start with this one! Yeah, I read your other thread that you so KINDLY linked here.

First of all, you should have asked this question: "Do you find a simple on-line calculator like this one useful? Or would you rather use the simple formula:

Wavelength (in meters) = 300 / Frequency (in MHz)"

Not the generalized, "Are "On LINE" calculators useful to you??"

Yes, yes. You are so smart. Quoting me out of context. Getting people to agree with your general statement about ALL on-line calculators, while I was being specific about very simple ones, such as the frequency/wavelength conversion or inch/metric conversions.

I never said ALL on-line calculators were a waste of space. If you read what most of your "supporters" say very carefully, you will see most of them agree with what I am saying:

"Personally I'd not have need for the calculator offered" - Kris

"I use online conversion calculators occasionally and think they can be very useful, especially when one needs to convert some arcane units." – Troy36

"A complex online calculator is ok." –Hendrik

"I find a few on line calculators to be very useful, and I rely on them regularly. Many are of no use to me but may be helpful to others. Some of them are truly junk," – Ace Boeringa

"Beats memorizing scores of formulae for converting this unit to that unit ad infinitum" –Dvader1000

"My >opinion<, they're a waste of server space and as already mentioned are usually full of ads. But that's just my opinion. For those who find them helpful, they probably aren't a waste of space" –JubaJabba

"They are useful...especially if you can't find a hardware one...or the one you do find hasn't the functions you need. ...I'm sure we all use the net for finding obscure data..." - Del the Cat

And Roxane went even further than I did when she said in reply to you, "I agree with the posts that disagreed with the use of calculators. That's why we lag in computational skills and the scientific knowledge to exceed countries that insist calculations be "brain-monitored"

Funny, your reply to her confirmed you were paraphrasing what I said. Too bad your "paraphrase" was INACCURATE! I NEVER said that all on-line calculators were useless or a waste. I also use them occasionally for obscure formulae and exotic unit conversions. My point was, and still is, CR4 declares itself a discussion place for Engineers. Engineers need to be familiar with basic scientific formula and unit conversion, and, yes, if you are an engineer and don't know this basic formula, then it IS a CRUTCH, not a tool.

Next time, better pick on someone who can't argue with your logical fallacies and your taking quotes out of context and inaccurate paraphrasing.

Anything more you might add will just be beating a dead horse so I suggest you just leave this one alone.

Have a great day

You too!

Blimey, is that it now?

Can I go home at last?

About the word "crutch"

It was said: If you feel the need to use such a crutch, ...

Ah, WHO decides something is a "crutch" and not a "tool"?

That is the question.

And the correct answer = ???

And the correct answer should be simple, since "crutch" and "tool" are simple words that convey a simple idea, correct?

See the third to last paragraph in my post #31 above.

So, most things are crutches to someone in this world.

IF it is your field, it is a crutch.

IF it isn't your field, it is a tool to be used.

Got it.

Thank you.

Ken

Well, yes, and no. If it is so simple and common, "even a caveman can do it" (apologies to GEICO), and you would expect the normal practitioner to have the inherent ability to perform without it, then it is a crutch. If it is somewhat more complex, arcane, or infrequently used, and there would be little value maintaining the ability personally, and more value in accessing it only when needed, then it could be a tool.

A M E N !

Do nothing simply if a way can be found to make it complex and wonderful !

Ah, The Witlessism of the Day award. Other candidates:

"If the design has been completed, then it just doesn't have enough features yet!"

"Remember, Murphy was an optimist!"

Or another, "Every Silver Lining has a cloud."

And of course, my favorite, "No good deed goes unpunished!"

Ah, YES! The TV is one of the world's biggest crutches!! Used by those who can't figure out how to entertain themselves without it.

Oops, same can be said for these computers too. Dang. That is a drag.

What the hell would I do without my 5 computers. I still ponder why one of my ex-wives said: You love that f***ing thing more than you love me.

A few years later... divorce, 1995 style. Remarried, divorce 1996 style. Wait a while longer, marriage 2000 style and then: I am young, (31, 30 when spoken) I am beautiful, (you can decide for yourself by looking at photos of her in one of my galleries) I am smart, (128-130IQ) you will never be rich, all you own is this old house and that old machine shop, AND, I deserve better than this... divorce 2006 style.

Ah, deserving of better! Maybe I am too? LOL

Still got my computers though! Without them as a crutch I don't know what I would do.

Strange how computers are or still seem to be a male thing. Although the last ex (Ani) can tear them apart and put them together and has 2 at the present time, I think that women like her are few and far between. Our 7 years (6 of marriage) were enjoyable for the most part, until she decided she had to live with a millionaire in a house worth over a million dollarsUS and go for joyrides in his two airplanes.

There is always hope... I hope.