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Floyd Davidson wrote: opcom wrote: Not studio quality. Studio quality AM is +/- 5KHz. "Studio quality AM" is not a valid term. AM Broadcast has never been up to "Studio Quality" standards, which would be _at_ _least_ 20 to 20K Hz. AM Broadcast Band quality is 5K Hz. It's semantics at this point, the AM studio is perfect if it is limited to about 5KHz, something which is quite a different case than an FM studio or a recording studio. +/- 3000-3500 Hz is communications quality, and fine for AM. but we don't need more rules. Why so wide? I answer below.. SSB? 2.5KHz is fine. I am speaking up for the old iron. I do limit my AM to +/-3KHz in the speech amp. There is no difference at all between the audio response necessary for SSB and AM. AM, because it has both sidebands, will necessarily take up twice the RF spectrum for the same audio response, but in fact 2.4KHz (400Hz to 2800Hz) is actually *preferable* to higher fidelity audio response when the purpose is voice communications. (Ma Bell did a bazillion studies on this decades ago, so it is not exactly new information.) Can you find this data for me? I am very interested, it might shed more light on the subject. I understand it may be hard to find today. Since SSB has no carrier, you can shave the bandwidth a little closer by getting rid of the lower frequencies. With AM, you may as well use the lower frequencies if you want, since you have a carrier at 0 Hz so to speak. 2.4KHz bandwidth on AM voice sounds a little muffled to me, and to me, 3.0KHz or (very) slightly more, is much more readable, especially when there is alot of noise. Everyone hears differently in some respect, maybe I have hearing damage. In amy case I am not advocating more than 'necessary', but I do have trouble with speech signals that are cut off too sharply. I always tune my SSB receiver so that the voice is higher pitched than natural, then it is easier for me to hear. It doesn't work with AM that way, the tuning. just as an example, 2.4KHz ssb = 300 to 2700 Hz audio. +/-2.4KHz AM = 0 to 2400 Hz audio. I can't remember what volume I read it in so take it with a grain of salt, or a whole bag of salt, but I recall that for good intelligibility and having a signal that does not tire the operators, there was some mathematical relationship between the highest and lowest audio frequencies to be reproduced. Anyone remember that? I regret I cannot quote the source. Maybe there is a some experimentation to be done. I would like to see a reprint of the Bell studies. But anyway, here are my sources to support the freedon to employ at least some leeway for bandwidth in the matter of communications quality AM. It's definitely your right to interpret them how you wish: ================================================== ======= "Understandable speech requires the reproduction of all frequencies from about 250 to 2700 cycles, or sideband frequencies ranging from 250 to 2700 cycles above and below the carrier frequency." FROM: "RADIO ENGINEERING", second edition, 1937, chapter 9, section 72, page 396, "Waves with Amplitude Modulation", Frederick Emmons Terman, Sc.D., Professor of Electrical Engineering, Stanford University. MY Opinion: Mr. Terman's text says 'requires', therefore this is taken as the minimum requirement for speech to be 'understandable'. This does not necessarily imply good communications quality, but rather 'understandability'. ================================================== ========== "Modulation frequencies Corresponding to Typical Signals (minimum frequency range that must be met)" "Long-distance telephone quality.......250-3500 c/s." FROM: "RADIO ENGINEERING", third edition, 1947, chapter 9, section 9-1, page 469, table 9-1 --Modulation frequencies Corresponding to Typical Signals (minimum frequency range that must be met)., Frederick Emmons Terman, Sc.D., Professor of Electrical Engineering and Dean of theSchool of Engineering, Stanford University. Past president, Institute of Radio Engineers. My Opinion: Please consider the audio quality of long distance telephone service in 1947. ================================================== ========== "...For ordinary SSB telephony, M=3000 Hz. .." "...For high quality SSB Telephony, M=4000Hz. ..." "...For ordinary DSB telephony, M=6000 Hz. ..." "...For high quality DSB Telephony, M=8000Hz. ..." FROM: "THE RADIO MANUAL", fourth edition, 1950, appendix 5, page 859, "Table of necessary bandwidths", George E. Sterling, Commissioner, Federal Communications Commission, and Robert B. Monroe, Radio Engineer, Columbia Broadcasting System, D. Van Nostrand Company, Inc. 4th edition, 1950. ================================================== =========== "Frequencies up to at least 2,500 cycles, and preferrably 3500 cycles, are necessary for good speech intelligibility." FROM: "RADIO HANDBOOK", fourteenth edition, 1956, chapter 12, section 12-1, page 225, Editors and Engineers, Ltd., edited by William I. Orr, W6SAI. ================================================== =========== "...Mediocre reproduction may be restricted to 100-5000 c/s., while many radio receivers are limited to 100-3500c/s. It should be remembered that the frequency range is taken as overall, including the loss of sidebands and including the loudspeaker. Wide frequency range is only comfortable to the listener so long as other forms of distortion are negligible." FROM: "THE RADIOTRON DESIGNER'S HANDBOOK, THIRD EDITION", 1941, chapter 5, page 32, "frequency distortion", THE RADIOTRON DESIGNER'S HANDBOOK, THIRD EDITION", F. Langford Smith, S.SC., Member I.R.E, M. I.R.E., A.M.I.E.E., A.M.I.E |
Floyd posted, in part:
There is no difference at all between the audio response necessary for SSB and AM. AM, because it has both sidebands, will necessarily take up twice the RF spectrum for the same audio response, but in fact 2.4KHz (400Hz to 2800Hz) is actually *preferable* to higher fidelity audio response when the purpose is voice communications. (Ma Bell did a bazillion studies on this decades ago, so it is not exactly new information.) --------------------- I'd like to make a few comments about this. 1. AM does not necessarily have two sidebands. The same "quality" is had with SSB AM and DSB AM, and SSB AM uses half the spectrum. 2. If the transmitted audio passband is 400 to 2800 Hz (2.4 kHz), the receiver passband still needs to be 2.8 kHz for correct demodulation. That is, the demodulation carrier must have the identical relationship to the sideband that existed at the transmitter. 3. During WWII the Bell system used as little bandwidth as 1.6 kHz in their long-haul channels. The quality was very poor, but you *could* communicate. Modern telecom channel bandwidth is about 200 Hz to 3450 kHz. Generally this is called a 3500 Hz channel. In ham radio that bandwidth provides good fidelity for speech. With anything less it becomes increasingly difficult to recognize who is the speaker. Using narrow band receive filters (1.8 to 2.4 kHz) improves the ability to communicate by eliminating or reducing QRM/QRN, but the quality is reduced by this. 4. Ma Bell's studies on fidelity got into the perceptual area of balance between the low end and high end of the audio spectrum; Having lots of bass without good treble, or good treble without good base did not sound good. That's one of the big reasons that the low end of the telecom voice channels don't start at 100 Hz or lower. I thought I had a copy of the study, but couldn't find it. I would like to see hams who like AM migrate to SSB AM and limit the audio passband to 3500 Hz. For carrierless SSB 3500 Hz should also be the passband limit. Don |
"Larry" wrote:
Floyd, I think it all boils down to this, if you want to limit the frequency range of your radio to whatever, because you believe that you like it best (or whatever) great! It is your privelege to do that. As for me, I think that a little wider is nicer and that's OK for me too. You may believe strongly in your justification but the rules give very wide lattitude in making this call to the amateur. Some may think this is about to change but I don't think so. So good luck and have fun. The hobby is great, isn't it! I did not suggest that there should be a regulatory limit. That came from elsewhere. My argument is purely one of technical aspects that have to be considered. However, if you and others insist on ignoring the appropriate technical aspects, we *will* see regulatory action to curtail it. By the way, in the discussion of bandwidths, your hyperbole is totally without meaning if you are not specifying attenuation at the given limits of bandwidth. 100 to 3500 hz is a very different spec if those are 3 db points than if they are 26 or 60 db points. Also specifying that the limits refer to peak or average would be helpful in making your comments meaningful. Yes, and I could write a ****ing book too. What's your point? The only time any specs that I meantioned deviated from the standard ones, I mentioned not only that it did but what the effect was. Besides not even a moose would take his call at being real with those kinds of limits. You're up there, go ask one! If you want your audio to attract moose, please get a bullhorn and head for the woods. But stay off the ham bands with it. While you are at it... Learn not to top post and learn to trim unnecessary quoted text. Bandwidth is important in places other than a ham rig too. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Floyd,
Being up there in Alaska isn't doing you much good. Sounds like you're not getting any. Tell you what, get your bullhorn, go out in the woods, call a moose .. hope for a female naturally .. well maybe not and maybe that's part of the problem, and come back to the group with a whole lot better attitude. Frankly people like you worry me with all that unfriendy hostility. You sound like an immature young stud who just need to mellow out. Oh BTFW Floyd, I'll post how and when I like and I'll leave any text attached that I think may be appropriate and when it becomes your newsgroup and you are made God, I might listen! Till then FO!! "Floyd Davidson" wrote in message ... "Larry" wrote: Floyd, I think it all boils down to this, if you want to limit the frequency range of your radio to whatever, because you believe that you like it best (or whatever) great! It is your privelege to do that. As for me, I think that a little wider is nicer and that's OK for me too. You may believe strongly in your justification but the rules give very wide lattitude in making this call to the amateur. Some may think this is about to change but I don't think so. So good luck and have fun. The hobby is great, isn't it! I did not suggest that there should be a regulatory limit. That came from elsewhere. My argument is purely one of technical aspects that have to be considered. However, if you and others insist on ignoring the appropriate technical aspects, we *will* see regulatory action to curtail it. By the way, in the discussion of bandwidths, your hyperbole is totally without meaning if you are not specifying attenuation at the given limits of bandwidth. 100 to 3500 hz is a very different spec if those are 3 db points than if they are 26 or 60 db points. Also specifying that the limits refer to peak or average would be helpful in making your comments meaningful. Yes, and I could write a ****ing book too. What's your point? The only time any specs that I meantioned deviated from the standard ones, I mentioned not only that it did but what the effect was. Besides not even a moose would take his call at being real with those kinds of limits. You're up there, go ask one! If you want your audio to attract moose, please get a bullhorn and head for the woods. But stay off the ham bands with it. While you are at it... Learn not to top post and learn to trim unnecessary quoted text. Bandwidth is important in places other than a ham rig too. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"Larry" wrote:
Floyd, Being up there in Alaska isn't doing you much good. Sounds like you're not getting any. Tell you what, get your bullhorn, go out in the woods, call a moose .. hope for a female naturally .. well maybe not and maybe that's part of the problem, and come back to the group with a whole lot better attitude. Frankly people like you worry me with all that unfriendy hostility. In other words, you don't have a valid response, and can only come up with "go call a moose". You sound like an immature young stud who just need to mellow out. *You* are the one posting "go call a moose" responses, kid. Oh BTFW Floyd, I'll post how and when I like and I'll leave any text attached that I think may be appropriate and when it becomes your newsgroup and you are made God, I might listen! Till then FO!! You don't have a clue about Usenet either, do you. Take a look at *any* of the thousands of Usenet guides on formatting articles. Take a look at RFC-1855. Do a google search on "netiquette". Nobody made me god, and that has nothing to do with your arrogant ignorance of what works and what doesn't, on Usenet or on ham radio. "Floyd Davidson" wrote in message ... While you are at it... Learn not to top post and learn to trim unnecessary quoted text. Bandwidth is important in places other than a ham rig too. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
As to SSB AM, (called "AM Equivalent" by the military) some radios will do this, but others won't.
The military surplus GRC-106 for instance does this, and the final is a linear amplifier with associated efficiency issues. To the listener, it sounds like AM, but they can tell that a sideband is missing if they tune around. The Johnson Viking for instance does not do it, and the final is a class-C stage modulated by a class AB2 push-pull stage. So some gear just can't do it. I don't prefer linear amplifiers as final stages for AM, but it's an opinion. There is nothing wrong with either mode. SSB AM can be used in the AM nets along with DSB AM. |
FO! ??
Flash Override -the FO key function on some military field phones. ... Till then FO!! |
In article , Floyd Davidson
writes: "Studio quality AM" is not a valid term. AM Broadcast has never been up to "Studio Quality" standards, which would be _at_ _least_ 20 to 20K Hz. Hey, even FM Broadcast is only up to 15 KC. At least that's been the limit since they added the stereo subcarrier. I agree that recording equipment should be good at least up to 20 K. There is no difference at all between the audio response necessary for SSB and AM. AM, because it has both sidebands, will necessarily take up twice the RF spectrum for the same audio response, but in fact 2.4KHz (400Hz to 2800Hz) is actually *preferable* to higher fidelity audio response when the purpose is voice communications. (Ma Bell did a bazillion studies on this decades ago, so it is not exactly new information.) During my years at Bell Labsm, working in speech coding, our preferred standard range was 300 - 3300 Hz. At 3300 you have a fighting chance of telling an "F" from an "S" and a "T" from a "D" sound. At 4000 you have very little trouble. At 2800 you have all those military types spelling it out with phonetics and lots of "say again". The low, bass end doesn't really affect BW much (not at all in AM with carrier), but too much bass wastes power and voltage swings in the modulator, and overlaods and distorts in the receiver's audio circuits and speaker, and also batters your ears. That's why a lot of radios have tone switch positionsthat cut out some of the bass response. 73, Mike K. Oscar loves trash, but hates Spam! Delete him to reply to me. |
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