Just What Is RF Anyway?

Hello there in Eatontown land,

The FCC defines RF as starting at 9 kHz since that is the frequency at which they begin allocating the spectrum. You mean the army doesn't have an official definition?

Thanks. I don't doubt they have that someplace but when I asked them directly, SEVERAL TIMES, I can't get an answer. I'm obviously not getting to the right people within the FCC but I'm not gonna give up. Thanks, though.

Ken

Mort,

Who would you recommend in the Army? As I've said, I've posed my question to many people in various commercial, Federal and military entities but haven't found the right person/organization yet.

Thanks.

Ken

Antennaman

I'm somewhat confused about your question... no offence intended, but what is there to ask? It's all pretty well defined.

If you have a long enough antenna you can xmit a 1hz signal. THe navy built an ELF station to talk to subs that used the earth as an antenna and required some incredible power and like 6000km long dipole. Operated at 50-85hz if I remember.

But a radio wave is just simply part of the electromagnetic spectrum. RF is from waaaay low to ~300ghz. somewhere around that microwave range the atmosphere jacks the signal...attenuates it..to be unusable until you get into IR.

But rf is rf. Lightning makes rf. Variable frequency drives on too long cables with unmatched motors will cause a reflected wave that you can hear with an a.m. radio.

It's just a part of the spectrum ...we just happen to find that we can modulate and demodulate it with our primitive signals.

Good Point and no offense taken. I see that even you have made a generalization by saying that "RF is from waaay low to ~300GHz" Have you ever been asked what "waaay low" is? I guess my frustration is that I'm interested in so many areas of RF and as a result, I come across many, many references to what RF is. I'm just trying to get back to the basics of physics on this. Why would one person (or for that matter orgainzation) refer to an alternating polarity signal as RF and another refer to that same signal as not (perhaps referring that 10kHz signal as audio, etc.). The IEEE, in their C95.1-2005 (Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3kHz to 300 GHz) obviously considers 3kHz to be RF while audio buffs would call that 3kHz an audio frequency. This was simply ONE example of what I'm referring to.

I've gotten into the physiology effects of contact and induced currents in the human body with regard to shocks, burns, skin-effect with regard to the body being subjected to alternating currents, voltages, etc. I even teach about some of these effects. I'm always looking for yet another effect (good or bad) when exposed to such alternating polarity signals, be they "RF" or not. I've always found that the more I understand, the better I can convey such concepts to those I teach, but I will always be looking for more information such as I am here.

I will admit, you do seem to have a fairly good grasp of the concepts but when we write to others, speak to others that may or may not be in our field of engineering, don't you ever wonder how you'd answer some of the questions that can pop up like "What is waaay low?" I'm not poking fun at you, only suggesting that we all take a moment to look at what we communicate with the "ear" of the lay person.

I still hope to see more discussion on my topic. We seem to go from electrical oscillations to mechanical oscillations to sound to non-ionizing radiation (RF to optical radiation) and eventually to ionizing radiation (e.g. x-rays, gamma radiation, etc.). I'm attempting to obtain a much better grasp of all of this, including all the uses, applications, effects on bilogical tissue, and on and on.

Thanks again for your reply.

Ken

interesting posts and even more interesting replies on the r.f. transmitted frequency effects.

ken the issue of human or animal physiologic injury goes back to preww2 days if you can find any of the that data start looking into Raytheon electronics contibution to the development of radar fo units the r.a.f had installed in b-17's. some info put out by mcgill university on it that could be a place to look in. that is probably protected under canada's official secrets act, theit is my suspicion it would be embarrasing to past and present governments if the research that was done by that instituion were found to have ended up at various times dprior to to and during that war in the hands of axis scientists and armies.(cordless electical power tools are not new) you my find your questions leading to a visit from the u.s. government's s.e.al. training programmes quartmaster security and surveillance agents or a opportunity to meet some of the homeland security agency personell.

A "Guest wrote the following (#15):

interesting posts and even more interesting replies on the r.f. transmitted frequency effects.

ken the issue of human or animal physiologic injury goes back to preww2 days if you can find any of the that data start looking into Raytheon electronics contibution to the development of radar fo units the r.a.f had installed in b-17's. some info put out by mcgill university on it that could be a place to look in. that is probably protected under canada's official secrets act, theit is my suspicion it would be embarrasing to past and present governments if the research that was done by that instituion were found to have ended up at various times dprior to to and during that war in the hands of axis scientists and armies.(cordless electical power tools are not new) you my find your questions leading to a visit from the u.s. government's s.e.al. training programmes quartmaster security and surveillance agents or a opportunity to meet some of the homeland security agency personell.

------------------------------------------------------

Ken's reply:

Sorry about having to call you "Guest" but hopefully you'll let us know what your name is, etc.

Guest, I have to say that you made me chuckle when you inferred I might be getting some curious phone calls and/or visits. I'd like nothing more ... since I work for them! But, I'd still like to know what THEY'D have to say about our roundtable! Thanks for the comments!!

Ken

I think there only seems to be an antagonism between the 3kHz beeing either RF or audio frequency. They may be both because noone prohibits that RF and AF may be overlapping.
Regards Uwe

First take a look at wikipedia...it says it well enough http://en.wikipedia.org/wiki/Radio_spectrum

If my well used up brain cells remember correctly ...IF is the beat freq in a receiver and also the freq on the input side of the superheterodyne modulator. RF is the final freq to be amplified and propagated at the antenna.

They use VLF for communication with submarines whilst submerged... dunno how Low the Frequency... but they use veeeeeeeeeeeeeeeeeery looooooooooooooooog aerials to tx and rx.

look here

Del

I can't believe you are trying to ask anyone for a specific frequency!... That is just nonsense...all you will get is an arbitary figure...

Heck I'll tell you any number you care to hear!

I think you have defined it quite well yourself as 'it can be "launched" into the air/freespace'.
Of course this is dependent on the antenna and the power of the transmitter... the whole electromagnetic spectrum is a continuum...

Definitions of 'bands' and allocations are purely a human construct for convenience.

The low and high frequency limits of today are different from those a century ago and doubtless a century hence... Don't worry about it

Del

Del,

I thank you for your reply. You are correct, of course, about the fact that what "we" have at one time referred to one signal as AF (audio frequency) and have later referred to that same signal as being RF. Yep, it may be arbitrary but if we can't "nail" such concepts down and for good reason, those we attempt to convey our knowlege to are likely to become confused and rightfully so. We often say an apple is an apple is aways an apple but are all apples the same? NO they aren't. I'm suggesting that you ask yourself some questions from time to time to challenge yourself for a better understanding of what you THINK you know. I mean no offense either. I mean when we speak of such concepts as RF, what it is, how it's "made," how it's launched into freespace, etc. we often wave our hands when explaining to our peers and in particular those of less understanding than ourselves. It's that waving that has always concerned me as I've attempted to learn more both in and outside my fields of study (e.g. going from E.E. to a solid understanding of physiology (e.g. electrotherapy, etc.) where alternating currents are used in the field of medicine. I feel guilty when I'm teaching someone when all I have is waving in an area. My question that kicked off this discussion was one of my attempts to fill in some blanks so there is less hand waving, on my part ... and perhaps for others here and outside this group.

Thanks for your comments.

Ken

Antennaman, I would avoid referring to a signal as just an rf signal, why not explain that it is an electromagnetic signal created and radiated by a wire carrying the electrical signal...

If you need to describe it in detail then I would recommend you read "Fields and Waves in communication systems".

An extremely good reference book which is crammed full of the maths you will need to explain thoroughly the concept of radiating waves.

I've only managed to read the first chapter in 30 years

If you just want a brief description then remember that the radiated field is of an electric field combined with a magnetic field... So perhaps you could explain how it works by example of the magnetic field surrounding a conducter in a solenoid and then a straight wire with the electric field generated by nature of the wavelength and hence the length of the aerial or transmission line?

John.

John,

I was purposely trying to refrain from referring to the signals as being RF or not since any sort of signal is just that, a signal whether it's modulated or not and regardless as to whether it's "launched" or not. I may check into your text reference but I can only buy so many texts and I LOVE technical reading and I guess that's why I'm so dense when it comes to sports or the news in the papers (other than what is on the tele. The way I figure it, I only have so many (and that's an unknown) years left to do what God put me on Earth to do and I'm still trying to figure out just what He had in mind so I keep trying. Anyway, in a thousand lives I'd never get to understand all that I'd want to understand and what good is knowlege if you don't use it or for that matter what good is knowlege if you can't "turn the light on" for someone who's interested but just hasn't figured out something yet. I love those looks from those I teach. There's nothing more spectacular. I surely got a kick out of your comment that you'd only gotten to read the first chapter of the referenced text in 30-years. Hey, join the crowd of those that read alot. At least you know what you read and you can always return to that reference (or others) to fill in any blanks in your understanding of whatever "flips your switch" as I like to say.

I'm quite familiar with the fact that a radiated "field" actually contains both an electric field and a magnetic time varying field and that both "propagate" at right angles to each other but I didn't want to go there yet. Your comment on the problems with the very low signals are that you can't modulate it, the way most of us think, with an audio signal with any kind of bandwidth since the signal isn't going to be as long (wavelength) as the modulating signal is in wavelength but see that only as a reason for asking yourself how ELSE can I modulate it before I "launch" it. That's the beauty of our minds. None of us can be experts in all fields, let alone in any one of them and that doesn't bother me at all. That's my reason for respecting those that know more than I do in any given specialty or field and hopefully they will recognize and appreciate what I have to offer at the "table." We are each an island until we reach out and join our peers, or for that matter experts in OTHER fields completely. I marvel at ALL the experts out there and I mean ALL of them from the electrician, the cable installer, the plummer, the sewer cleaner, the shoe-shiner and on and on. Wouldn't we all like to learn to be better at almost anything? I would. Sure, I might be able to do plumbing or electrical work but I really marvel when I see a master in his or her own trade doing their "thing." I just wish they didn't assume that because of what I wear each day that I'm some kind of stiff shirt. Ok, on to my next posting. Great job, John!

Ken

Perhaps you would care to comment on #7.

Regarding Audio frequencies...this is a dangerous missnomer as you know 'audio' is sound waves. Of course you can have an electromagnetic waves at these frequencies... but they would be best called something other than 'audio'.

One reason we don't bother with low frequencies is that you will have difficulty transmitting usefull data on a low frequency carrier. E.G. It would self evidently be difficult to modulate music (from say 30hz to 20khz) onto a carrier below 20khz.

I hope this helps to clarify the difference between what I think I know and what I actually know

Del

Hey there, Del,

You're getting to be a habitual contributor! I hadn't seen your number 7 comment yet but I will and I WILL comment on it you can be sure! With regard to your comment above (#13). I guess my overall comment is "Very Good!" You and I are like two automobiles driving on two non-parallel roads. They're just "bound" to intersect in the future. You'll see what I mean in a future post ... regarding one of your OTHER posts.

As far as your comment that you hoped that we'd see the difference between what you THINK you know and what you ACTUALLY know. Well, that doesn't concern me. I like what I'm seeing already so keep it up!

Ken

Del,

Boy, when I read your post I wanted to tell you that you'd just about hit on one of my MAIN questions. Continue reading since as I recall you may have hit on it in a future post. I don't want to tell you where and how you just about hit on it but it will be clear on one of my upcoming posts/replies. Thanks again!

Ken

wonderment of just how low in frequency a signal can be transmitted??

If pressed for the lowest frquency... I'd say events like the reversal of the Earths magnetic poles possibly transmitted incredibly slow but incredibly weak signals.

The problem is defined as much by what we can detect as what we can transmit.
What we detect is also governed by what we are actually looking for!
I don't s'pose anyone is looking for signals of 10^-12Hz ! But it doesn't mean they don't exist.

Hey I'm beginning to realise why it's making you think! Good question!

Del

As far as I'm aware audio frequencies are limited to those that the human ear can hear, and by that description alone means that they are pressure variations of the atmosphere and not part of the electromagnetic spectrum?

Audio frequencies can easily be converted into radiated electromagnetic waves transmitted by an antenna so the only distinction between rf and af is that the rf is an electromagnetic signal which can be transmitted in a vacuum. As opposed to audio which can only be heard through a gaseous medium...

Does that help anyone? Or am I adding fuel to the fire?

John.

Electroman,

I can tell you're one of those that needs to open his thinking to other than the limits of human capabilities. If we all did that we'd never give a crap about optical wavelengths above (or actually shorter than) those that we humans can perceive. Can you immagine where we'd be without RF? After all, we can't hear that or see that either! When we take a look at the electromagnetic spectrum and check out the narrow slice that we humans can perceive it's pretty sad. Honey bees can see the UV range and that's how they know which flowers to go to. Sure we are smart enough to make a converter of sorts to see the same wavelengths but no where as compact as the capability given to the bee. We design so many things that essentially make up for the fact that we cannot see or hear or perhaps feel "things" that are there but we weren't designed for some of those detection schemes. No, you didn't add fuel to the fire. You made a great comment that afforded me the privilege to open some more eyes and brains, so THANKS! You gave us all some other things to think about. Good job!

Ken

If pressed for the lowest frquency... I'd say events like the reversal of the Earths magnetic poles possibly transmitted incredibly slow but incredibly weak signals.

The problem is defined as much by what we can detect as what we can transmit.
What we detect is also governed by what we are actually looking for!
I don't s'pose anyone is looking for signals of 10^-12Hz ! But it doesn't mean they don't exist

Del, why would you surmise that?

Again, the inquirer asks a reasonable question. Let's provide them with reasonable answers and the very best we have to offer. Interestingly enough, and for a change, our inquirer here (so many others do not, little info/reference) comes across quite well with very good and bona-fide comprehensive question.

You otherwise seem to be to probably be a very intelligent person and delivers good responses. With that, you have my admiration!

Del, Del, Del. My, my my. Yet another post! Ok, you asked for it. In fact Del and Bill ML have hit my reason for writing you all. DEAD ON! Bill ML, I'll write you directly so hang in there but I wanted to recognize your keen sense of where I'm going with all this just as Del has. Specifically (with regard to Del for now), Del made the statement or question? right off and that was the following:

"wonderment of just how low in frequency a signal can be transmitted??" Yes, absolutely! That's what us RF types wonder about. Surely we design antennas and the like to sent out higher and higher frequencies/signals and the benefits of those higher frequencies are that you can develop quite a lot of gain and many other characteristics with the higher frequencies but what about "transmitting" signals at the lower ends of the spectrum? How about under water? How about in a cave, way down in the earth? Del's comment about if we transmit it can someone detect it. Dead on, Del! After all, what good is a signal if you can't use it or make use of it. Perhaps it was only meant to be a one-way signal. Sure, that's possible but I'm more of a two-way kinda guy. Del's comment about folks not probably looking for signals of 10^-12Hz but that doesn't mean they don't exist. That hits on another nerve of mine (that means interest for you all), extraterrestrials, visits from other beings, etc. Hey, how many of you are so ignorant that you think that God coudn't make beings smarter that we are and more develped? Do you HONESTLY think He dusted His hands off on the Seventh Day and said I'm done? No, I don't think so and neither should you.

Another great post, Del. Thanks.

Ken

There has been a number of good explanations here; but one that has been missed: The common denominator - HOW the energy is transposed or propagated.

For example: Even given even a 1 Hertz generated signal to a 1/2 wave antenna (however quite large), you will have an RF signal propagated and electromagnetic in nature. Drive the same to a "speaker"/acoustical transducer (that is what it IS) and you have audio, however not discernible by the human ear.

There are barriers defined by our technology that move our definitions for basically audio, radio frequency (microwave being the same), and light spectrum's (however with various photon and other theory). Again, where one comes into play and another disappears, seemingly, is only the method it is originated (with transducer/antenna/other). The other remains to be of interest to me. For instance, I believe that we could transmit the light spectrum with an 'antenna' but there is no technology where we can do that (using conversion methods such as lasers, lamps and LED's) and where (an those others are substituted as some sort of 'transducer', but in fact they are not, only a method). The physics rather wane at some point into that spectrum yet. But then what about the photon theory? Is there a transition to mass somewhere? Is it valid? Not discounting it at all, the photon theory might be a clue into a whole different realm of transmitting, as we know it. Certainly would lead to other innovative.

As I've said elsewhere in another forum, I believe that there is another method of communication/propagation not yet discovered. Maybe to circumvent the proverbial speed of light limitation.

BTW: I believe that the FCC is very much understaffed these days and does not have the resource to respond to much of the inquiries they likely receive each day.

To our inquirer Antennaman: Hope this helps.

Bill ML,

I hope it's not a sin that I've not been rating the individual posts as I think that tends to stiffle our current thinking trend and Bill ML, you get the GOLDEN Prize for landing straight on one of my recent TOP questions for many, many technical types I hang out with and converse with both in the Government and in the private sector. Drum roll, please maestro!

I knew I could count on all of you and while what I'm about to say (or actually write) isn't the only question I have, it is one of my TOP questions so I don't want to abandon my original question, that of trying to answer what makes a signal turn into a RF signal but, once we get a satisfactory answer to that my next question was going to be what Bill ML asked, "HOW the energy is transposed or propagated."

DING, DING, DING, DING!!!! Ok, folks, let's not forget MY Question but let's ALSO try to wrestle with Bill ML's question. Good Going, Bill!

Once we have an answer for what yields/defines a signal as RF and that signal is applied to the terminals or feed of our antenna .... I think I'd like to keep it a RF signal that's not yet a field so no waveguide theory yet. We have this current heading to the antenna via the transmission line and eventually to the antenna itself. What are the conditions for that signal to be radiated or "launched" as I like to call it, from that antenna? Obviously, any signal will be radiated, or will it? Afterall, if the signal isn't made to mate with the antenna, i.e. meet up with an antenna that is resonant with the antenna, the signal may still radiate but not as well or as efficiently as one that is DESIGNED for that antenna ... or vise-versa. We can make any conductor radiate but there are conditions that must be met to OPTIMIZE the antenna to efficiently radiate the signal. I'll leave this here for you or our other contributors to ponder and provide posts but I wanted to make one other comment to you, Bill; You've not only discovered where I've been going but you've taken it a bit farther so I hope someone will take your ponderings and take it to the next level and/or expand on it somewhat with some thoughts. I will certainly look forward to those that take your "bait" and run with it.

I've got to get back to my work here in the office but I'll be reading and hopefully post again tomorrow. I'll be reading the other posts that I didn't have time to comment on today but I will.

Ken

OK, I've read a lot of this and I'm not sure the nuances are captured so let me give it a shot.

RF is radio frequency and the reason some frequencies are chosen as radio frequencies is that they propigate well in free air. Some also have a nice habit of bouncing off the ionosphere, so you can transmit RF over long distances if you want. It was the trial and error approach of the early radio pioneers that pretty much came up with the limit of what is RF and what isn't.

Of course you can communicate with submerged subs at th 50-80Hz range because the signal will couple through the air / water interface at these frequencies rather than being completely reflected as higher frequencies are. Of course the data rates at such low frequencies are painfully slow, but subs typically aren't going anywhere fast anyway.

Audio frequencies are the range of human hearing, typically 20Hz-20kHz. Of course that implies sound pressure, which is air pressure. But you have to have an amplifier to produce the energy that drives the speaker, so audio frequencies are also electronic.

As technology and understanding have expanded the frequencies used by radio have expanded, so most frequencies can now be considered RF. But RF usually connotes communication purposes and the technolody associated with that.

Well, that's my 0.02 euros.

Eric, I have to kind of agree and kind of disagree with you on this. It all depends on how much a person goes with "accepted" definitions.

Based on "accepted" definition...day-to-day go to the stereo shop definition... you will hear people say that the signal from a stereo amp output is AF. You will also hear people say that, with regards to a xmitted or received signal, RF is from antenna to antenna.

But...by proper definition...audio frequency = audible frequency = a frequency, a physical vibration however generated, that is audible to the human ear. By proper definition...until the signal is converted from electrical energy to mechanical energy by the work of the coil it is RF.

But does that matter?..not really...even though I know the difference, I still find that I call the output from my amp to be AF, I guess.

Same with RF...talk with 5 guys, get 5 answers. I did 10yrs in the Air Force doing comm/nav. We were trained that once you hit carrier freq for final transmission, regardless of modulation or amplification ... you had RF. Has nothing to do with an antenna or not. Once you go from IF to RF ... even in the cable ...you still got RF. The OP was asking what the true proper definition of when RF becomes RF so I thought I'd throw a couple more of my pennies in the pile...

Alternate the current at any radio Hz and get RF.

Leave a solder peak on a motherboard and get RF. Leave two peaks the same length then send and receive making a nightmare to troubleshoot from the logic test.

Rf will come off any wire/antenna when the field changes. How efficiently it propagates is a function of length, shape, and environment.

Is there a connection to whether the signal can be connected to an "antenna" of proper length (I'm assuming it would be a dipole) and expect it to be launched into freespace BECAUSE of it's FREQUENCY?

Yes, Basically an antenna tuner modifies the circuit into acting like different lengths for optimal receiving/transmitting. dipole or not.

With a name like Antennaman I'm sure you know this already.

Brad

Hi Antennaman,

The book IEEE Standard Dictionary of Electrical and Electronic Terms defines Radio Frequency thusly:

(1) (Loosely) The frequency in the portion of the electromagnetic spectrum that is between the audio-frequency portion and the infrared portion.

(2) A frequency useful for radio transmission. Note: The present practical limits of radio frequency are roughly 10 kilohertz to 100,000 megahertz. Within this frequency range, electromagnetic radiation may be detected and amplified as an electric current at the wave frequency.

The book Reference Data for Radio Engineers gives designations for frequency ranges as follows:

30 to 300 hertz: Extremely Low Frequency

300 to 3000 hertz: Voice Frequency

3 to 30 kHz: Very Low Frequency

30 t0 300 kHz: Low Frequency

300 to 3000 kHz: Medium Frequency

3 to 30 MHz: High Frequency

30 to 300 MHz: Very High Frequency

300 to 3000 MHz: Ultra High Frequency

3 to 30 GHz: Super High Frequency

30 to 300 GHz: Extremely High Frequency

Hope this helps. Regards,

S

I seem to be so inspired to be locked into the new respondents here this evening.

We can cite IEEE, FCC CFR and other references all day long; but likely Antennaman (our inquirer) has already seen these. Definitions,and that's all they are; and these do not answer this question, only to place some sense of 'law' that is otherwise of use as a reference.

So far, I believe that my earlier comments contain the answer, and where the reader should take notice that I did not make any reference to frequency/wavelength limitations. The transmission method is the key and limitation. I stand on that.

Excuse me, but he was asking for a definition. That's what I gave him.

Surely the only useful definition is any frequency which can be transmitted through a non electrically conductive medium (and received with an antenna), and, can be useful OR can cause a problem.

Hi Antennaman (it's obvious),

Your question has been adequately answered (any frequency can be transmitted, and is, therefore RF). What really do you want? You have us all confused. Do you want to know at what frequency and what power an RF signal becomes dangerous? Do tell.

S

Hello all. I've been extra busy at work and at home preparing for my divorce so haven't had much Xtra time on my hands so I feel badly about not getting back any sooner. My court case, after almost two years of this stuff is tomorrow (2/13) so I hope that does it. Nuff on that though. No, I'm not done with this thread and will return in a couple of days so hang on there, StandardsGuy. While I am multi-task oriented on this, there are several parts; 1. Under what conditions and/or signal characteristics do we classify that signal as being RF? 2. If part and/or all of those conditions are that it be ABOVE some frequency (take note at what the IEEE has used for their IEEE C95.1 2005, which uses 3kHz but has some good information in Annex C of that document about why the frequencies were chosen or implies same, etc.). 3. Can that signal at this special frequency be launched by an antenna of classical sense (e.g. half-wave dipole) in all cases or are there conditions which must be met that are not simply the usual speed of light divided by the frequency (but take into account the thickness of the elements and the end-effect/end effects? Most inportantly, 3. Once this RF signal which now has the required time varying electric field and magnetic fields or currents that are applied to the antenna ... just how the heck is the signal, now a combination electric and magnetic field, LAUNCHED? What "pushes" the signal off the antenna so that it is replaced by the next cycle or wavelength? Do you (not just you StandardsGuy) see what I'm getting at? The bottom line is we can all SAY that something happens but if we truly don't understand HOW it happens, we cannot grow in our fields.

As far as when a RF signal becomes dangerous, I haven't asked that one. To answer that question many more must be asked. We can get there, just not yet. Let's see what thoughts come forth on this reply. Some of you may think that I know the answers to some of these questions. As far as I'm concerned, until I know all the criteria that must be met and the conditions for radiating/or launching a timevarying signal that has a mathematical relationship to the physical length of the "antenna" I'm not happy with myself. I want MORE INPUT as the "Short-Circuit" robot would say.

The more we REALLY understand the basics the better we can be at teaching those behind us. I'll NEVER feel like I'm done learning and am frustrated that I only have one lifetime (that I know of) to gather as much knowledge as I can and challenge those behind me to learn as well.

There are several other mini-threads where this discussion can go so I hope we still have some interest in answering some of the questions I've asked here today.

Standards Guy, thanks for asking the questions you did. They were fair and very useful as a springboard for my answer.

Ken

Hi Antennaman,

I sympathize that a divorce is on your plate. I hope I have not caused any hard feelings. The distraction is expected, and may God be with you in moving forward.

I also sympathize with wanting to understand more deeply the subject of antennas (or any other). That is the frustration with quantum mechanics and cosmology that are some of my interests.

"1. Under what conditions and/or signal characteristics do we classify that signal as being RF?"

I think it depends on who is classifying it, and what their motives are.

"3. Can that signal at this special frequency be launched by an antenna of classical sense (e.g. half-wave dipole) in all cases or are there conditions which must be met that are not simply the usual speed of light divided by the frequency (but take into account the thickness of the elements and the end-effect/end effects? Most inportantly, 3. Once this RF signal which now has the required time varying electric field and magnetic fields or currents that are applied to the antenna ... just how the heck is the signal, now a combination electric and magnetic field, LAUNCHED? What "pushes" the signal off the antenna so that it is replaced by the next cycle or wavelength?"

This is the more interesting question. I'll give you some thoughts I have on it. You know, no doubt, that an antenna must match the impedance of the transmission line or some of the power will be reflected back to the transmitter. I have some experience in this area (SWR meters and impedance bridges). In my opinion, the purpose of the antenna is to match the impedance of the transmission line to the air (in the case of air transmissions). Part of the process is to make the antenna resonant to the applied frequency. End effects have an effect on resonance. Thickness of the conductor effects capacitance which affects resonance too. An antenna can be shorter that 1/2 wavelength if there is an inductor to make it resonant. Does it transmit as well? I don't think so. I think the impedance is not as well matched to the air. There is also the effect of radiating in a different direction than you wanted. Does this partially answer your question? Anybody else have thoughts on this?

S

The dipole 1/2 wavelength radiator is of a standard reference and with purpose. It is the most effective radiator; that is, that it propagates the best transfer into the either. In free space, it is optimum, all other exhibits attenuation.

The intrinsic impedance of transmission in propagating to a dipole antenna tends to land on about 50-100 ohms.

The lowest frequency? Believe earlier that I cited 1 Hz perhaps as an example, but there's no reason why any fraction of a Hertz can be transmitted, and please: let's keep the subject matter limited to sinusoidal. A square wave or other complex makes it just that: Complex and further subjective.

But back to a transmitter operating below about 30 KHz, and in particular in the subaudible range: At some point, it ends up becoming a direct current amplifier because of related component limitations. Modulating such any signal with certain technique could be a problem (see below). Similarly, receiving would be interesting; and where a basic and very old technology would have to be retrieved; but back to: TRF, and "tuned radio frequency". This had no intermediate conversion, but now thinking about it, wonder if it is viable? Maybe, for some rudimentary application. Never toyed with it. Maybe with SAW technology, one could achieve recovery of data/audio/whatever on that below 30 KHz (e.g) but the lower the frequency, the less bandwidth available to transmit/recover/receive.

On a practical side, transmitting an EM signal below some 30 KHz perhaps would probably be not well propagated. Those attuned to the US Navy sub comms fleet broadcast technique would know that they achieved and worked well for quadrants of the earth, but takes a lot of power=megawatts.

There are limitations of propagation that limit us to transmission of RF energy.

Point-to-point, or line of sight, virtually never is often a problem. In the physical world there has been some reliance on the upper layers for transmitting beyond the horizon, by reflection. But those proven not to be reliable nor really predictive.

All frequencies will be RF as all voltage signals radiate even DC.

If you want to carry information modulated on to these signals DC would be a bad choice though and so would be anything less than few kHz as you would have a small band width and not much information could be carried.

When the transmission carrier wave is of a low frequency even a 1/4 dipole is going to be long so as you raise the frequency you get lots of benefits for costs for transmission and reception but if the frequency get too high you then have problems like beam width etc and the cost starts to rise again so with current technology we tend to use RF as a term for our systems in use.

I don't know anyone with a 3Km long transmitter so they can communicate with submarines but I know lot's of people with transistor radios and cell phones.

Possibly just a misinterpretation of the RF term by the industry.