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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-low carrier frequency
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 -- 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
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 |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
... You are an idiot ... bother some one who has the time to take you to task ... JS |
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. |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 6/30/07 11:27 PM, in article , "John Smith
I" wrote: Don Bowey wrote: ... You are an idiot ... bother some one who has the time to take you to task ... Open your mind. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 30, 2:55 pm, John Smith I wrote:
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 radium, I applaud you in your interest generating discussion. if there are no questions there are no answers; dumb or smart! to me your questions came across wonderfully, and generated both responses. as humans we stand on two legs, most of us that is. men get the honor and privilage to stand on three legs from time to time. this is our blessing and our curse! ps. how would u like to change the cell phone industry? and your discussion group of course! remeber all things are possible!!!!!!!!!!!!!!!! |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
Open your mind. Geesh! Hook up a 20X linear behind an xmitter and see if you can't find some artifacts ... JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
DTC wrote:
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. The Coax we used for the repeaters was fed with 250-0-250V DC and the current was regulated at 49mA. The only time the cable jointers worked on it the power feed was disabled. |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 8:05 AM, in article , "John Smith I"
wrote: Don Bowey wrote: Open your mind. Geesh! Hook up a 20X linear behind an xmitter and see if you can't find some artifacts ... JS Sheesh.... That has nothing to do with helping someone understand AM. It appears you are more interested in dumping your blog on this board, than providing something to clarify the real answers for an electronic novice. |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 8:05 AM, in article , "John Smith I"
wrote: Don Bowey wrote: Open your mind. Geesh! Hook up a 20X linear behind an xmitter and see if you can't find some artifacts ... JS By the way, I have. A 10B to a GPT750. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
That has nothing to do with helping someone understand AM. It appears you are more interested in dumping your blog on this board, than providing something to clarify the real answers for an electronic novice. So, you will decide what he needs to know and what he doesn't? If he becomes aware of the more esoteric and trivial it is dangerous. Get real control freak! JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 8:39 AM, in article , "John Smith I"
wrote: Don Bowey wrote: That has nothing to do with helping someone understand AM. It appears you are more interested in dumping your blog on this board, than providing something to clarify the real answers for an electronic novice. So, you will decide what he needs to know and what he doesn't? If he becomes aware of the more esoteric and trivial it is dangerous. Get real control freak! JS You really are thick headed if you can read Radium's posts and can't see how he can't even deal with the real topic, much less the junk you toss in. The more esoteric material should come after there is a grasp of the basics. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
You really are thick headed if you can read Radium's posts and can't see how he can't even deal with the real topic, much less the junk you toss in. The more esoteric material should come after there is a grasp of the basics. What, you have already given up on him and consigned him to a special education class? Damn, I missed him being that dense, of course I tend to give everyone the benefit of the doubt--even you ... JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
John Smith I hath wroth:
RHF wrote: ... Because "Radium" Touched Them With A Thirst For Knowledge And A Quest For Answers. ... I don't know, according to any instructor I have ever had respect for: "There are NO stupid questions, only stupid people who are afraid to ask questions." I beg to differ. My favorite mentor/instructor/employer had a different philosophy regarding questions and answers. His line was something like "If you don't understand the problem, no solution is possible". His method was to concentrate on understanding the problem, refining the corresponding questions, and only then concentrating on finding the answer. I would spend much more time thinking about "what problem am I trying to solve" instead of blundering prematurely toward some potentially irrelevant solution. My problem with the original question is that it fails to associate itself with anything recognizable as a real problem to solve or a theory to expound. In my never humble opinion, if there was a question under all that rubbish, it was quite well hidden and severely muddled. He also introduced a substantial number of "facts" that varied from irrelevant to incoherent to just plain wrong. The problem for us in not in finding the answer, but in decoding the question. There may not be any stupid questions, but there seem to be a substantial number of marginal people asking questions. I answer some techy questions in alt.internet.wireless. What I see, all too often, are people that seem to think that no effort on their part is necessary to obtain an answer. They exert no effort to read the FAQ, no effort to supply what problem they are trying to solve, and no effort to supply what they have to work with. In this case, Mr Radium has either exerted no effort to compose his question in a form that can be answered, or if there was such an effort, it has failed miserably. He couldn't even find a suitable collection of newsgroups for his question. There may not be any stupid questions, but there certainly are questions not worth the time attempting to answer. If Mr Radium had left the question at the subject line: "AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency" the question would have been easy to answer, as several people have done. However, those that answered and I all did the same thing. We extracted from the word salad question what we thought was something resembling a coherent question, and ignored the rest of the rubbish. In other words, we did the necessary simplification and problem reduction, and discarded the bulk of the incoherent residue. There may not be any stupid questions, but if you bury it under a sufficient number of words, it may closely resemble a stupid question. Depends ... I guess. JS Well, let's see: http://groups.google.com/groups?as_q=%22guess%28tm%29%22&as_uauthors=Jeff+L iebermann 533 guesses, out of about 16,000 postings, which I guess(tm) isn't all that bad. -- 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 anastronomically-low carrier frequency
On 7/1/07 8:55 AM, in article , "John Smith I"
wrote: Don Bowey wrote: You really are thick headed if you can read Radium's posts and can't see how he can't even deal with the real topic, much less the junk you toss in. The more esoteric material should come after there is a grasp of the basics. What, you have already given up on him and consigned him to a special education class? Damn, I missed him being that dense, of course I tend to give everyone the benefit of the doubt--even you ... JS As a matter of fact, as you should be able to see, I am working here in support of his learning process while you do nothing but rag on in support of your blog. |
AM electromagnetic waves: 20 KHz modulation frequency on anast...
Radium wrote:
"I have a very weird question about electromagnetic radiation, carriers, and modulators." It makes no difference which signal you call the modulating signal and which you call the carrier. Modulation is simply mixing the two together at a nonlinear point to create new frequencies along with the originals. The same modulation products are produced by 20 Hz on a 20 KHz carrier or 20 KHz on a 20 Hz carrier. The nonlinear point may be a single diode, a diode bridge, or a high-level plate modulator. The signals out can be the same except for amplitudes. I think Ian Jackson has also given a correct answer that is more complete though less simple. Best regards, Richard Harrison, KB5WZI |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
As a matter of fact, as you should be able to see, I am working here in support of his learning process while you do nothing but rag on in support of your blog. idiot JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 11:11 AM, in article , "John Smith I"
wrote: Don Bowey wrote: As a matter of fact, as you should be able to see, I am working here in support of his learning process while you do nothing but rag on in support of your blog. idiot JS OK, you win. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
[pure crap!] "In the mid-1870s, a form of amplitude modulation—initially called "undulatory currents"—was the first method to successfully produce quality audio over telephone lines. Beginning with Reginald Fessenden's audio demonstrations in the early 1900s, it was also the original method used for audio radio transmissions, and remains in use by some forms of radio communication—"AM" is often used to refer to the mediumwave broadcast band (see AM radio)." Taken from this URL: http://en.wikipedia.org/wiki/Amplitude_modulation And, please read the WHOLE PAGE before making a larger idiot of yourself ... JS |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 11:19 AM, in article , "John Smith I"
wrote: Don Bowey wrote: [pure crap!] "In the mid-1870s, a form of amplitude modulation‹initially called "undulatory currents"‹was the first method to successfully produce quality audio over telephone lines. Beginning with Reginald Fessenden's audio demonstrations in the early 1900s, it was also the original method used for audio radio transmissions, and remains in use by some forms of radio communication‹"AM" is often used to refer to the mediumwave broadcast band (see AM radio)." Taken from this URL: http://en.wikipedia.org/wiki/Amplitude_modulation And, please read the WHOLE PAGE before making a larger idiot of yourself ... JS I didn't read the link, as it has nothing to do with this string. You posted to Radium's question about Amplitude Modulation, saying that on a telephone line, the DC voltage is the Carrier and the microphone current (or voltage if you prefer) is the modulation. Now THAT is un-pure crap and it is what I responded to and which you deleted in this post hoping to look better, which you don't. I already conceded to your ignorance, so you really didn't need to post more, but thanks for the opportunity to help. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Don Bowey wrote:
[more crap!] Oh, that explains it, your understanding of amplitude modulation is: AM = Black Magic. ROFLOL! JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jul 1, 7:24 am, wrote:
radium, I applaud you in your interest generating discussion. if there are no questions there are no answers; dumb or smart! to me your questions came across wonderfully, and generated both responses. as humans we stand on two legs, most of us that is. men get the honor and privilage to stand on three legs from time to time. this is our blessing and our curse! Thanks for your understanding. ps. how would u like to change the cell phone industry? Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. As I learned recently, 40 KHz is the minimum radio frequency required to coherently transmit/receive audio signals. The highest sound a human can hear is 20 KHz. The radio-frequency used must be at least 2x the intended frequency of the information being transmitted/received. I chose 285 KHz to be the highest radio frequency for cell-phones because it is roughly the highest-frequency categorized as "long wave" radio. and your discussion group of course! You mean the anti-yahoo group? http://groups.google.com/group/yahoo...s?lnk=li&hl=en |
"Radium" [email protected] COMPLETE IDIOT..........
"Radium" wrote in message oups.com... On Jul 1, 7:24 am, wrote: Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. I chose 285 KHz to be the highest radio frequency for cell-phones because it is roughly the highest-frequency categorized as "long wave" radio. IDIOT!......complete idiot...... |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Sun, 01 Jul 2007 12:16:35 -0700, Radium
wrote: On Jul 1, 7:24 am, wrote: radium, I applaud you in your interest generating discussion. if there are no questions there are no answers; dumb or smart! to me your questions came across wonderfully, and generated both responses. as humans we stand on two legs, most of us that is. men get the honor and privilage to stand on three legs from time to time. this is our blessing and our curse! Thanks for your understanding. ps. how would u like to change the cell phone industry? Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. --- Good idea. The available spectrum between 40kHz and 285kHz is 245kHz wide, so at a little less than 3kHz per channel the maximum number of channels available would be 82. That means that no more than 82 people can be on the air at the same time. Probably all over the world, to boot, what with those frequencies being able to propagate over long distances. That's probably a good thing, because with those 1875 meter long 1/4 wave whips at 40kHz and those 263 meter 1/4 wave whips at 285kHz on the mobiles, any more people on the air than that would certainly create a hazardous situation. -- JF |
AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
On 7/1/07 11:53 AM, in article , "John Smith I"
wrote: Don Bowey wrote: [more crap!] Oh, that explains it, your understanding of amplitude modulation is: AM = Black Magic. ROFLOL! JS OK you stupid ****, I'm almost out of patience with your ignorance. I was hoping you might learn something, but I see that is unlikely. AM is a process of frequency multiplication. Now you tell me where you think such multiplication takes place on a phone line, and I'll follow-uo by telling why you're full of crap. SIMECS! |
"Radium" a COMPLETE IDIOT... - More Likely An In-Complete-Want-To-Be [.]
On Jul 1, 12:50 pm, "Porgy Tirebiter" wrote:
"Radium" wrote in message oups.com... On Jul 1, 7:24 am, wrote: Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. I chose 285 KHz to be the highest radio frequency for cell-phones because it is roughly the highest-frequency categorized as "long wave" radio. - IDIOT!......complete idiot...... PT - Once again why waste your time replying to his posts ? ? ? {Oops Like I Am Doing Too !} Actually "Radium" would appear to be an In-Complete-Want-To-Be driven by the 'urge' to Post these Forever Ponding Questions for others to charge at like Don Quijote's quest to slay Windmills {a fool's errand} http://en.wikipedia.org/wiki/Don_Quixote http://en.wikipedia.org/wiki/Fool%27s_errand FWIW - While many of his Post might fit into the "sci.electronics.basics" NewsGroup; often they would be consider OFF-TOPIC in other NewsGroups like : rec.radio.shortwave, rec.radio.amateur.antenna, alt.cellular.cingular, alt.internet.wireless, etc IMHO - In another life "Radium" would have made a great High School Science Teacher : Who's Students when on to do great things with their lives : Because "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" is just being 'radium'. http://en.wikipedia.org/wiki/Radium -alas- Our "Radium's" 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 an astronomically-low carrier frequency
Radium hath wroth:
ps. how would u like to change the cell phone industry? Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. Analog cell phones are going to be history in the US on Feb 18, 2008. Japan killed off analog around June 1999, Korea in Jan 2000, most of Europe in 1997, etc. 40KHz thru 285Khz? Great idea. Just one minor problem. A 1/4 wave antenna at about 100Khz frequency is 750 meters long. That's going to be a rather large antenna for literally dragging behind you. Maybe a balloon? Maybe a loop like this one? http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10850 Of course propagation might be a problem, as it will only work at night and you'll have to connect to a cell site on the opposite coast for those frequencies to work. The customers can be ignored when they complain about atmospheric static and noise. Of course, 240KHz of usable bandwidth is much less than the hundreds of MHz currently in use by cellular providers, so there will substantially fewer users. Let's see.... there are 240 million subscribers in the US. Your AM system can handle about 40 users (6KHz channels), so your cell phone bill will only be 6 million times larger than it is currently. Now do you see why the microwave bands are so in demand for cellular. As I learned recently, 40 KHz is the minimum radio frequency required to coherently transmit/receive audio signals. Coherently? I would be worried if you planned to incoherently transmit/receive audio signals. Perhaps if you added 40KHz to your word salad, it would make your blather more coherent. (Hint: Look up the definition of coherent and then use it where appropriate). Actually, you're close. 40KHz is the common frequency used by ultrasonic TV remote controls. I've seen PWM modulation system using a pair of these to act as a crude cordless phone (that doesn't require FCC type certification). You could probably go down to 20KHz, but then intermodulation products (mixes) between the audio and the carrier will begin to be a problem. Congratulations, you got one thing mostly correct. The highest sound a human can hear is 20 KHz. Voice is from 300 to 3000Hz. You could probably get away with 300 to 2400Hz. If you're planning to transmitting AM hi-fi or data, then you might need the 20KHz. The radio-frequency used must be at least 2x the intended frequency of the information being transmitted/received. Ummm... no. You're apparently thinking of the Shannon rule for information bandwidth: http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem If your input audio is perhaps bandwidth limited to 3KHz, a 6KHz carrier will not work. You'll get considerable mixing (aliasing) and audio intermodulation crud. The carrier would need to be somewhat higher in frequency as limited by whatever output RF filtering is used. I chose 285 KHz to be the highest radio frequency for cell-phones because it is roughly the highest-frequency categorized as "long wave" radio. Nope. See details at: http://en.wikipedia.org/wiki/Longwave -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
"Radium" a COMPLETE IDIOT... - More Likely AnIn-Complete-Want-To-Be [.]
On 7/1/07 2:11 PM, in article
, "RHF" wrote: On Jul 1, 12:50 pm, "Porgy Tirebiter" wrote: "Radium" wrote in message oups.com... On Jul 1, 7:24 am, wrote: Analog cells phones should stop using FM and should start using AM between frequencies of 40,000 to 285,000 Hz. I chose 285 KHz to be the highest radio frequency for cell-phones because it is roughly the highest-frequency categorized as "long wave" radio. - IDIOT!......complete idiot...... PT - Once again why waste your time replying to his posts ? ? ? {Oops Like I Am Doing Too !} Actually "Radium" would appear to be an In-Complete-Want-To-Be driven by the 'urge' to Post these Forever Ponding Questions for others to charge at like Don Quijote's quest to slay Windmills {a fool's errand} http://en.wikipedia.org/wiki/Don_Quixote http://en.wikipedia.org/wiki/Fool%27s_errand FWIW - While many of his Post might fit into the "sci.electronics.basics" NewsGroup; often they would be consider OFF-TOPIC in other NewsGroups like : rec.radio.shortwave, rec.radio.amateur.antenna, alt.cellular.cingular, alt.internet.wireless, etc IMHO - In another life "Radium" would have made a great High School Science Teacher : Who's Students when on to do great things with their lives : Because "Radium" Touched Them With A Thirst For Knowledge And A Quest For Answers. But a teacher MUST be rational. You rate Radium with more potential than I can. This most recent post is really off the wall. -but- These NewsGroups are NOT a High School Science Class -and- "Radium" is just being 'radium'. http://en.wikipedia.org/wiki/Radium -alas- Our "Radium's" 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 an astronomically-low carrier frequency
"Ian Jackson" wrote in message ... In message , cledus writes snip 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 Actually there would be no phase flip. cos(-a) = cos(a) 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. A double-balanced mixer is a multiplier. A * B = B * A [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, What's 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. You did pretty good. Ian. -- -- rb |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Jeff Liebermann wrote:
40KHz thru 285Khz? Great idea. Just one minor problem. A 1/4 wave antenna at about 100Khz frequency is 750 meters long. That's going to be a rather large antenna for literally dragging behind you. Well, your math is correct. However, the so-called "atomic" wrist watches receive their time signal from WWVB which transmits at 60kHz. How do they get that 1250 meter long antenna ( 1/4 wave at 60 kHz) inside that itty bitty wrist watch case? ;-) |
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