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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
Hi:
Please don't be annoyed/offended by my question as I decreased the modulation frequency to where it would actually be realistic. I have a very weird question about electromagnetic radiation, carriers, and modulators. Is it mathematically-possible to carry a modulator signal [in this case, a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared on a AM carrier signal whose frequency is 10^-(1,000,000,000-to-the-power-10^1,000,000,000) nanocycle* every 10^1,000,000,000-to-the-power-10^1,000,000,000 giga- eons and whose amplitude is a minimum of 10^1,000,000,000-to-the- power-10^1,000,000,000 gigaphotons per 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond? If it is not mathematically-possible, then please explain why. 10^-(1,000,000,000-to-the-power-10^1,000,000,000) second is an extremely short amount of time. 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond is even shorter because a nanosecond is shorter than a second. Giga-eon = a billion eons Eon = a billion years *nanocycle = billionth of a cycle Gigaphoton = a billion photons 10^1,000,000,000-to-the-power-10^1,000,000,000 -- now that is one large large number. 10^1,000,000,000 = 10-to-the-power-1,000,000,000 So you get: (10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) 10^-(1,000,000,000-to-the-power-10^1,000,000,000) = 10^-(10-to-the- power-1,000,000,000)-to-the-power-(10-to-the-power-1,000,000,000) 10^-(10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) is an extremely small number at it equals 10-to- the-power-NEGATIVE-[(10-to-the-power-1,000,000,000) to the power (10- to-the-power-1,000,000,000)] No offense but please respond with reasonable answers & keep out the jokes, off-topic nonsense, taunts, insults, and trivializations. I am really interested in this. Thanks, Radium |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Radium wrote:
... Is it mathematically-possible to carry a modulator signal [in this case, a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared on a AM carrier signal whose The 20 Khz is obviously NOT an audio tone, but exists as VLF, what you are terming "modulation" is actually a mixing of carriers then ... and the problem with your question ONLY BEGINS there! JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 29, 8:08 pm, John Smith I wrote:
The 20 Khz is obviously NOT an audio tone, Yes it is. 20 KHz is the highest audible frequency. Humans hear from 20 to 20,000 Hz. No offense but WTF are you thinking?? but exists as VLF, what you are terming "modulation" is actually a mixing of carriers then ... and the problem with your question ONLY BEGINS there! A carrier wave is modulated by the modulator wave. On most AM stations, the modulator wave consists of the voice of someone speaking. Most AM stations have carrier frequencies in the medium wave band - in the range of 520,000 to 1,160,000 cycles every 1 second. In the case I am describing, the modulator wave is a 20 KHz pure sine- wave tone on a carrier frequency of 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanocycle every 10^1,000,000,000-to-the- power-10^1,000,000,000 giga-eons. Is this scenario mathematically- possible? If not, then why?? |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Radium wrote:
WTF are you thinking when you describe the 20 Khz signal as, "a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared" One square meter of copper wire squared, a squared meter of modulation xfrmr ... ? Your question sounds like one of a high school physics student attempting to ask a seemingly logical--yet complex question, and of no real world value. Your ability at obfuscation is only mundane ... If what you say is true, you have an interest, what is the purpose of your question? JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 29, 9:15 pm, John Smith I wrote:
Radium wrote: WTF are you thinking when you describe the 20 Khz signal as, "a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared" One square meter of copper wire squared, a squared meter of modulation xfrmr ... ? Sorry that should be 1 X [10^-6] Watts-per-m^2 http://www.glenbrook.k12.il.us/GBSSC...nd/u11l2b.html 1 X [10^-6] Watts-per-m^2 is about the loudness of a "normal conversation" according to the above link. F-------------------king typos!!!!!!!!!! Your question sounds like one of a high school physics student attempting to ask a seemingly logical--yet complex question, and of no real world value. Your ability at obfuscation is only mundane ... If what you say is true, you have an interest, what is the purpose of your question? My basic question is if I have an AM receiver which receives signals on a carrier frequency of Fc, is it mathematically-possible for me to receive a modulator signal -- on that station -- of a frequency higher than Fc? If not, then why? If not, then how are the submarines which use ELFs [Extremely Low carrier Frequencies around 3 to 30 Hz] able to perform voice communications? I just stretched the question out to astronomical extremes. I have a habit of doing that. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In rec.radio.amateur.antenna Radium wrote:
Hi: Please don't be annoyed/offended by my question as I decreased the modulation frequency to where it would actually be realistic. I have a very weird question about electromagnetic radiation, carriers, and modulators. Is it mathematically-possible to carry a modulator signal [in this case, a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared on a AM carrier signal whose The fact that you specified the modulation in W/M^2 immediately says you don't know WTF you are talking about and the question is meaningless. You can AM modulate any frequency 0 Fc infinity with any other frequency 0 Fm infinity. Whether it's physically possible or results in massive distortion is a separate issue. snip inane crap -- Jim Pennino Remove .spam.sux to reply. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Radium" wrote in message ps.com... My basic question is if I have an AM receiver which receives signals on a carrier frequency of Fc, is it mathematically-possible for me to receive a modulator signal -- on that station -- of a frequency higher than Fc? If not, then why? If not, then how are the submarines which use ELFs [Extremely Low carrier Frequencies around 3 to 30 Hz] able to perform voice communications? I just stretched the question out to astronomical extremes. I have a habit of doing that. Why not simply ask the question you mean to ask, then, rather than the absurd numbers you put in the original version of this (and which you then expect everyone to work through, just to see what the hell you might be talking about)? The answer to the question you seem to be asking is obvious if you simply work through the mathematics of what is going on in amplitude modulation. So why not simply do that, and not ask such incredibly obtuse questions? One hint: the ELF submarine communications to which you refer are NOT carrying voice communications, but very low-rate CW ("Morse code," if you want to think of it that way) signalling. Bob M. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
["Followup-To:" header set to sci.electronics.basics.]
On 2007-06-30, John Smith I wrote: Radium wrote: WTF are you thinking when you describe the 20 Khz signal as, "a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared" Candela Admittedly an odd unit to use for radiation at that frequency. Bye. Jasen |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Radium" is a well known "Troll".
When he runs low/out of meds and tin foil he will post this techo-babble crap all over usenet. Just add him to your killfile list. "Radium" is a "Throw-away"....a complete waste of time...... |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 30, 3:32 am, "Mike Kaliski" wrote:
It is not possible to modulate a carrier frequency at a frequency higher than the carrier frequency. Why not? I am getting conflicting answers. Some say it's possible to modulate a carrier frequency at a frequency higher than the carrier frequency, others say it isn't. Who is right? |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Radium wrote:
... I am getting conflicting answers. Some say it's possible to modulate a carrier frequency at a frequency higher than the carrier frequency, others say it isn't. Who is right? Radium: Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice), (hint, your telephone line is an example) right? However, when you get into RF--possible, usable, desirable are seperate and distinct things. Again, with simple logic, modulating a 30 CPS signal with limited voice freq (say 5K wide) is going to create a LOT of harmonics and mixed signals, ain't it? Suggesting a very wide band receiver would be needed to begin with ... in my humble opinion, and for various reasons, NO, it is NOT possible ... Regards, JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In rec.radio.amateur.antenna Radium wrote:
On Jun 30, 3:32 am, "Mike Kaliski" wrote: It is not possible to modulate a carrier frequency at a frequency higher than the carrier frequency. Why not? I am getting conflicting answers. Some say it's possible to modulate a carrier frequency at a frequency higher than the carrier frequency, others say it isn't. Who is right? The defining equations, you blithering idtiot. Here they are for the last time: http://ccrma.stanford.edu/~jos/mdft/...lation_AM.html -- Jim Pennino Remove .spam.sux to reply. |
(OT) : Radium - In Another Life You Would Have Made A Great High School Science Teacher
RADIUM,
IMHO - In another life "Radium" you would have made a great High School Science Teacher : Who's Students when on to do great things with their lives : Because You "Radium" Touched Them With A Thirst For Knowledge And A Quest For Answers. -but- These NewsGroups are NOT a High School Science Class -and- "Radium" you are just being 'radium'. = http://en.wikipedia.org/wiki/Radium decaying into a gas and dispersing into nothingness. http://en.wikipedia.org/wiki/Radon -alas- "Radium" Your Half-Life of Readable Interest http://en.wikipedia.org/wiki/Half-life is at best about 16.04 Seconds ~ RHF |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Radium" wrote in message oups.com... On Jun 30, 3:32 am, "Mike Kaliski" wrote: It is not possible to modulate a carrier frequency at a frequency higher than the carrier frequency. Why not? I am getting conflicting answers. Some say it's possible to modulate a carrier frequency at a frequency higher than the carrier frequency, others say it isn't. Who is right? Radium Me Read my entire earlier reply. Then go to the library and spend several years reading through the electronics section with particular emphasis on the origins of electrical technology and early wireless. Then take a technical biased university course incorporating logic and critical analysis and all will become clear. Without a basic knowledge of the subject, you are unable to make any form of critical judgement as to the accuracy or correctness of what people are telling you and all your questions become valueless because you do not have the nous to evaluate the answers you receive. Start with the basics and then try working up from there. Many inadvisable things are technically possible, putting a dead short across the mains will generate a pretty good example of electromagnetic pulse, but it is far better to use a capacitive discharge circuit to do the same job. You could try modulating carriers at all different sorts of frequencies to generate harmonics, far better to use a square wave generator. You get the idea. Regards Mike G0ULI |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 30, 3:46 pm, Jeff Liebermann wrote:
With AM, it's ALWAYS the high frequency that acts as the carrier and the lower that acts as the modulation. In AM, isn't the carrier the signal which always maintains a constant frequency and only varies by amplitude? If a carrier signal varies by anything other than just amplitude, then it isn't AM. Right? |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Radium wrote:
... If a carrier signal varies by anything other than just amplitude, then it isn't AM. Right? Let logic be your guide, again. As was pointed out earlier, the voice freqs which modulate the carrier will cause a variance in freq (a small fm component.) In fm, it is not unusual for a small "amplitude modulation" to be generated, as the varying/spanning of freq(s) is caused by the modulation, some changes in fm carrier can be generated. In an imperfect world, nothing is "perfect." Regards, JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
Radium hath wroth:
On Jun 30, 3:46 pm, Jeff Liebermann wrote: With AM, it's ALWAYS the high frequency that acts as the carrier and the lower that acts as the modulation. In AM, isn't the carrier the signal which always maintains a constant frequency and only varies by amplitude? You really are clueless. The carrier does NOT vary in amplitude. If it did, that would be modulating the carrier, which is the job of the modulator, not whatever is producing the carrier. You could have two modulators in series, that would make the circuit overly complicated. Please re-read my highly simplified previous explanation about the symmetry of the AM multiplier (mixer) input ports until it's absorbed and understood by your porous brain. Incidentally, the reason I keep using the term "multiplier (mixer)" is to avoid confusion with a harmonic multiplier. An AM modulator is a mixer, not a harmonic multiplier. Also, the carrier might remain constant frequency, for a given FCC channel assignment, but the modulation is all over the place. For example, your voice goes from 300 to 3000Hz, all of which is fed to the modulator for digestion. Conventional TV is VSB (visidual side band) which is a form of AM with one of the two side bands partially removed, usually by filtering. There's a carrier 1.25MHz offset for the video, another carrier 4.5Mhz offset for the audio, and whatever else they can throw in for low speed data. Two more more carriers are required for TV+audio. If you want to get really high-techy, the new digital modes (DRM, iBiquity, HD Radio, etc) all have multiple carriers, each of which is modulated individually. Same with various OFDM modes, which have multiple carriers, individually modulated and positioned orthogonally from each other to prevent mutual interference from adjacent modulated carriers. If a carrier signal varies by anything other than just amplitude, then it isn't AM. Right? Wrong. The carrier can also vary, such as in a sweep generator or jammer. It's not commonly done but it's possible. Want to obliterate the entire AM broadcast band? No problem. Just sweep the carrier from 530KHz to 1650KHz, while modulating the 300 to 3000Hz audio with a rendition of your incoherent ranting. By the way, you're welcome. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Radium" wrote in message ups.com... On Jun 30, 3:46 pm, Jeff Liebermann wrote: With AM, it's ALWAYS the high frequency that acts as the carrier and the lower that acts as the modulation. In AM, isn't the carrier the signal which always maintains a constant frequency and only varies by amplitude? If a carrier signal varies by anything other than just amplitude, then it isn't AM. Right? Essentially correct. The sidebands either side of the central carrier wave contain the modulation information. If the carrier wave were to shift in frequency then that would be frequency modulation. Before you ask, yes it is possible to have an AM signal modulating an FM one and several other wonderful combinations involving phase transformations, variable pulse widths and sideband(s) only. It is all detailed in the ARRL Handbook, RSGB Handbook and many other prestigious publications. Mike G0ULI |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 30, 7:43 pm, Jeff Liebermann wrote:
The carrier does NOT vary in amplitude. If it did, that would be modulating the carrier, which is the job of the modulator, not whatever is producing the carrier. Exactly. The modulator signal modulates the carrier wave. If there is no modulator signal, then the carrier does not vary by amplitude or by anything. One poster stated that the signal with the higher-frequency is automatically the carrier wave while the signal with the lower- frequency is automatically the modulator wave. This is not true. What I was trying to say is that an AM radio carrier wave cannot vary significantly by anything other than its amplitude [though, as one poster pointed out, the AM carrier can experience extremely-negligible variations in frequency]. If an AM radio signal has that restriction, it is the carrier wave. If an AM radio signal does not have that restriction, then it is the modulator wave. This is true, even if the AM carrier wave is of a lower-frequency than the modulator wave. That's what I was trying to say. In AM radio, determining which is the carrier wave and which is the modulator wave is not by which has the higher frequency but rather by which has the restriction that I stated. If there is no modulator signal, then no carrier signal of any type [AM, FM, etc.] will vary by any quality [frequency, amplitude, phase, etc.] |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 7:31 PM, in article , "John Smith I"
wrote: Radium wrote: ... If a carrier signal varies by anything other than just amplitude, then it isn't AM. Right? Let logic be your guide, again. As was pointed out earlier, the voice freqs which modulate the carrier will cause a variance in freq (a small fm component.) This will not happen in a properly designed transmitter. It is not a characteristic of AM. In fm, it is not unusual for a small "amplitude modulation" to be generated, as the varying/spanning of freq(s) is caused by the modulation, some changes in fm carrier can be generated. In an imperfect world, nothing is "perfect." Regards, JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
... This will not happen in a properly designed transmitter. It is not a characteristic of AM. In fm, it is not unusual for a small "amplitude modulation" to be generated, as the varying/spanning of freq(s) is caused by the modulation, some changes in fm carrier can be generated. In an imperfect world, nothing is "perfect." Regards, JS Listen to a "strong--pure am signal" on an fm receiver, turn up the volume on the fm receiver, something is responsible for that ... repeat experiment with the reverse ... "imperfect world theory" proof! In new equip (I started out decades ago, remember) voltage regulation, filters, suppressors have much improved ... digital processing is king and allows what analog never could achieve ... Regards, JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 8:29 PM, in article , "John Smith I"
wrote: Don Bowey wrote: ... This will not happen in a properly designed transmitter. It is not a characteristic of AM. In fm, it is not unusual for a small "amplitude modulation" to be generated, as the varying/spanning of freq(s) is caused by the modulation, some changes in fm carrier can be generated. In an imperfect world, nothing is "perfect." Regards, JS Listen to a "strong--pure am signal" on an fm receiver, turn up the volume on the fm receiver, something is responsible for that ... repeat experiment with the reverse ... "imperfect world theory" proof! You are hearing the effects of the sidebands, not the Carrier. In new equip (I started out decades ago, remember) voltage regulation, filters, suppressors have much improved ... digital processing is king and allows what analog never could achieve ... Regards, JS In a properly designed transmitter the Carrier amplitude does not change with modulation. I have better tools than FM receivers to prove that fact and theory agree for AM. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
Radium hath wroth:
On Jun 30, 7:43 pm, Jeff Liebermann wrote: The carrier does NOT vary in amplitude. If it did, that would be modulating the carrier, which is the job of the modulator, not whatever is producing the carrier. Exactly. The modulator signal modulates the carrier wave. If there is no modulator signal, then the carrier does not vary by amplitude or by anything. Brilliant. Yes, if there is no signal input, there's no change in output. Incidentally, in an AM system, the carrier does NOT change. You can see that on a spectrum analyzer. Modulate all you want and the carrier stays put at 50% of the total power output. The rest of the power is split between the upper and lower side bands. If there is no modulation input, then the side bands disappear, but the carrier just stays there. As someone mentioned, there is usually some residual FM on the carrier usually caused by sloppy power supply regulation. Also, some synthesizer noise. A well designed AM broadcast transmitter doesn't have much of this junk present. The problem is that the FM that appears on the carrier also appears on all the side bands. It doesn't hurt if the carrier has a little residual FM, but any such junk on the sidebands will result in a substantial increase in audible noise by mixing with the audio. One poster stated that the signal with the higher-frequency is automatically the carrier wave while the signal with the lower- frequency is automatically the modulator wave. That was me. This is not true. Prove it. I explained how it works and why quite adequately. I didn't even need to resort to formulas and calculations. The multiplier (mixer) modulator inputs are symmetrical and identical. Therefore the inputs are also symmetrical and indistinguishable. I also provided a simple audio test you can do in your spare time to demonstrate how it works. Now, convince me that the multiplier (mixer) waveform would be different depending on which input was the carrier or modulation. What I was trying to say is that an AM radio carrier wave cannot vary significantly by anything other than its amplitude [though, as one poster pointed out, the AM carrier can experience extremely-negligible variations in frequency]. If an AM radio signal has that restriction, it is the carrier wave. If an AM radio signal does not have that restriction, then it is the modulator wave. This is true, even if the AM carrier wave is of a lower-frequency than the modulator wave. That's what I was trying to say. I give up. What you've done is created a word salad. That's where you have a mess of buzzwords, shredded together, mixed with some window dressing, and served in a manner to imply that you have a clue what you're disgorging. Even the most basic concepts are not sinking in. You've also ignored multiple suggestions to read some very fine sources on how RF and modulation works. Open book, insert face, and come back when you have a clue as to the basics. In AM radio, determining which is the carrier wave and which is the modulator wave is not by which has the higher frequency but rather by which has the restriction that I stated. Wrong. With AM it's easy. The higher frequency is always the carrier. Can you give me a diagram or a commonly used communications system where the reverse might be true? I can't. If there is no modulator signal, then no carrier signal of any type [AM, FM, etc.] will vary by any quality [frequency, amplitude, phase, etc.] Yawn... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
... You are hearing the effects of the sidebands, not the Carrier. DUH! And, you only have the sidebands as a result of the carrier/modulation ... In a properly designed transmitter the Carrier amplitude does not change with modulation. I have better tools than FM receivers to prove that fact and theory agree for AM. And the time to argue the insignificant ... sharpen that razor blade, you can then successfully split much narrower hairs ... JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 30, 12:55 pm, John Smith I wrote:
Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice), (hint, your telephone line is an example) right? The telephone does not use either AM or FM. It is simply the electrical equivalent of the sound that gets into the microphone. You input a 1 KHz tone into the microphone, telephone lines will carry a 1 KHz AC current to the destination. The louder the sound into the microphone, the stronger the amperage in the telephone lines. |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 8:50 PM, in article , "John Smith I"
wrote: Don Bowey wrote: ... You are hearing the effects of the sidebands, not the Carrier. DUH! And, you only have the sidebands as a result of the carrier/modulation ... So what? You implied or inferred that what was heard from the FM radio was caused by the AM Carrier. Leave out the Carrier and you will hear the same thing. In a properly designed transmitter the Carrier amplitude does not change with modulation. I have better tools than FM receivers to prove that fact and theory agree for AM. And the time to argue the insignificant ... sharpen that razor blade, you can then successfully split much narrower hairs ... It is important that we not confuse a person new to electronics by the type of inane points you make. It doesn't matter a whit if someone's AM transmitter Carrier shifts on power peaks due to poor regulation. It has nothing to do with "AM" and everything to do with poor design. Side issues don't help the new folks. JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Mike Kaliski wrote:
ELF communications are carried out at very slow data rates, only a few characters per hour at best. Actually its on the order of several characters per minute using a 64 character "alphabet". It is possible to communicate at a base band frequency of 0Hz. This is what happens when you talk down a hard wired telephone or intercom. At a telephone exchange (switching centre), the signals from each line are modulated onto a higher frequency for onward transmission down a trunk wire cable or fibre optic cable. The multiplexed high frequency modulated signals are down converted back to audio frequencies once they reach the intended destination. In the old T carrier (before 24 channel digital T1) carrier, each telephone conversation was modulated onto a low frequency radio frequency AM signal ranging from (and don't quote me as its been over thirty years since I worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Radium wrote:
You input a 1 KHz tone into the microphone, telephone lines will carry a 1 KHz AC current to the destination. The louder the sound into the microphone, the stronger the amperage in the telephone lines. On a side note, its actually voltage modulation towards the subscribe and current modulation back to the central office. The earpiece is a high impedance (2,000 ohm) device that responds to voltage variations. The carbon microphone element 220 to 200 ohms modulates the talk battery current. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Jeff Liebermann wrote:
DTC hath wroth: Mike Kaliski wrote: ELF communications are carried out at very slow data rates, only a few characters per hour at best. Actually its on the order of several characters per minute using a 64 character "alphabet". It is possible to communicate at a base band frequency of 0Hz. This is what happens when you talk down a hard wired telephone or intercom. At a telephone exchange (switching centre), the signals from each line are modulated onto a higher frequency for onward transmission down a trunk wire cable or fibre optic cable. The multiplexed high frequency modulated signals are down converted back to audio frequencies once they reach the intended destination. In the old T carrier (before 24 channel digital T1) carrier, each telephone conversation was modulated onto a low frequency radio frequency AM signal ranging from (and don't quote me as its been over thirty years since I worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band. Argh, that brings back fond nightmares of Ma Bell. 4Hz per voice channel with FDM (frequency division mux). Most were FM systems, but there were some AM implimentations (to avoid patent infringement). Later, there were SSB systems that doubled the number of channels. No voice Spectrum BW channels KHz kHz AT&T ITU-T 12 60-108 48 Group Group 60 312-552 240 Supergroup Supergroup 300 812-2044 1232 Mastergroup 600 564-3084 2520 Mastergroup 3600 564-17548 16984 Jumbogroup That does bring back memories. I worked on STC built systems that used AM modulation using Double-Balanced Modulators and depending on "Group" classification used either the lower or upper sideband. Up to the 60 "voice" Ch's, we had some low Baud rate Modems on as well with the signalling frequency disabled, the spectrum usage was the the same however the next step up was 16 Supergroups using 60-4028KHz with Supergroup 2 not being translated. We also had a 30 Ch PCM link which worked very well apart from the "Regenerators" being susceptible to lightning. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In message , cledus
writes Radium wrote: Hi: Please don't be annoyed/offended by my question as I decreased the modulation frequency to where it would actually be realistic. I have a very weird question about electromagnetic radiation, carriers, and modulators. No offense but please respond with reasonable answers & keep out the jokes, off-topic nonsense, taunts, insults, and trivializations. I am really interested in this. Thanks, Radium The fundamental answer is no, it is not possible to generate AM where the baseband signal is a pure 20 kHz sinewave and Fc20kHz. The reason is that the modulated waveform consists of the sum of a sinewave at Fc, a sinewave at Fc+20kHz, and a sinewave at Fc-20kHz. If Fc20kHz then one of the components becomes a "negative" frequency. So the carrier must be greater than the baseband signal to prevent this. I'm afraid that this is not correct. The 'laws of physics' don't suddenly stop working if the carrier is lower than the modulating frequency. However, there's no need to get into complicated mathematics to illustrate this. Here is a simple example: (a) If you modulate a 10MHz carrier with a 1MHz signal, you will produce two new signals (the sidebands) at the difference frequency of 10 minus 1 = 9MHz, and the sum frequency of 10 plus 1 = 11MHz. So you have the original carrier at 10MHz, and sideband signals at 9 and 11MHz (with a balanced modulator - no carrier - only 9 and 11MHz). (b) If you modulate a 1MHz carrier with a 10MHz signal, you will produce two new signals (the sidebands) at the difference frequency of 1 minus 10 = minus 9MHz, and the sum frequency of 1 plus 10 = 11MHz. The implication of the negative 'minus 9' MHz signal is that the phase of the 9MHz signal is inverted, ie 180 degrees out-of-phase from 9MHz produced in (a). So you have the original carrier at 1MHz, and sidebands at 9 and 11MHz (again, with a balanced modulator - no carrier - only 9 and 11MHz). The waveforms of the full composite AM signals of (a) and (b) will look quite different. The carriers are at different frequencies, and the phase of the 9MHz signal is inverted. However, with a double-balanced modulator, you will only have the 9 and 11MHz signal so, surprisingly, the resulting signals of (a) and (b) will look the same. [Note that, in practice, many double-balanced modulators/mixers put loads of unwanted signals - mainly due the effects of harmonic mixing. However, the basic 'laws of physics' still apply.] Finally, although I have spoken with great authority, when I get a chance I WILL be doing at test with a tobacco-tin double-balanced mixer, a couple of signal generators and a spectrum analyser - just to make sure that I'm not talking rubbish. In the meantime, I'm sure that some will correct me if I'm wrong. Ian. -- |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Jeff Liebermann wrote:
Argh, that brings back fond nightmares of Ma Bell. And of splicing damaged buried plant in a wet trench...that stuff had a bite to it. |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 10:44 PM, in article
et, "DTC" wrote: Mike Kaliski wrote: ELF communications are carried out at very slow data rates, only a few characters per hour at best. Actually its on the order of several characters per minute using a 64 character "alphabet". It is possible to communicate at a base band frequency of 0Hz. This is what happens when you talk down a hard wired telephone or intercom. At a telephone exchange (switching centre), the signals from each line are modulated onto a higher frequency for onward transmission down a trunk wire cable or fibre optic cable. The multiplexed high frequency modulated signals are down converted back to audio frequencies once they reach the intended destination. In the old T carrier (before 24 channel digital T1) carrier, each telephone conversation was modulated onto a low frequency radio frequency AM signal ranging from (and don't quote me as its been over thirty years since I worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band. The O Carrier systems went from a low of about 32 kHz up to 164 kHz if I remember right. And the mainstay of long-haul communications (L Carrier) channel bank, was 64 - 108 kHz. One of the most strange Carrier Systems I worked with was a 1930s vintage H Carrier, one channel ssb "system" operating at about 12 kHz, and it ran without automatic synchronization. That was in the 60s. We used it as a maintenance channel in a voice over data configuration for a gap-filler radar site. I've never seen a more extreme merging of old and new technologies. Don |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 11:25 PM, in article , "John Smith
I" wrote: Radium wrote: ... You miss the simple point, the dc is the carrier ... instead of dc, you could put a 1 hz signal on the line and modulate it with your voice, indeed, you can put a 30 hz signal on the line and modulate it with your voice--if you can tollerate a bad 30 hz hum! But, who knows, perhaps you are tone deaf to the 30 hz hum and would like it ... JS But you miss the basic point...... The topic was Amplitude Modulation. |
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