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DSB SC Mode
Hello All:
Yeah Double Side band, suppressed carrier. A lot of the CB radios use to transmit DSB, not SSB. Many commercial radios did also in commercial use. But as time has allowed for circuits to be made around a integrated circuit, SSB Single Side band has taken over, as its more efficient. Ya get more effective output with SSB than DSB. Jay in the Mojave |
DSB SC Mode
On a sunny day (11 Jun 2006 06:53:18 -0700) it happened "Telstar Electronics"
wrote in .com: Jay, Yes... SSB has it's advantages... but several disadvantages. The main reason I stay away from SSB is the critical tuning. Somebody always comes on sounding like Donald Duck... LOL. I spend more time tuning people in then talking to them. And then there's the three way conversation... where you have to tune back and forth between the other two guys. Forget it. And last, there's alway the fact that until the CBs reach a stable operating temperature... your tuning like crazy. Nope, SSB is not for me... I have my DSB-SC... and it doesn't have those problems. Something wrong here, DSB-SC received on a normal set can only be made 'inteligible' if it is received as SSB. SSB is simply one sideband of the 2 DSB sends, so your BFO is [just as] critical. If you BFO is of center (so you re-insert the wrong carrier) and your RX filter already removed the other sideband, then you have all the 'duck' sound of SSB. Moderns CB sets have no 'DSB' option, only USB / LSB, so always use one sideband. In case a set DOES pass both sideband, you get double the problem.... Maybe you mean something else by DSB-SC altogether? Leave SOME carrier? |
DSB SC Mode
Not sure what you're talking about. When I say DSB... I'm referring to
what others call the AM mode. www.telstar-electronics.com |
DSB SC Mode
On a sunny day (11 Jun 2006 13:35:21 -0700) it happened "Telstar Electronics"
wrote in .com: Not sure what you're talking about. When I say DSB... I'm referring to what others call the AM mode. www.telstar-electronics.com DSB-SC (as you originally referred to) stands for: Double Sideband Suppressed Carrier. So, if the carrier is surpressed, then you have only 2 sidebands if a signal is present (single tone modulation), nothing if no modulation is present. http://www.ece.drexel.edu/courses/ECE-S306/lab3.pdf Look at figure 4, for a single tone modulating audio signal. You will notice it is quite different from AM! Normal AM is also DSB, but the carrier is not surpressed. Better to say AM if you mean AM, DSB is often used for DSB-SC. |
DSB SC Mode
I looked at your document. It's exactly what I'm talking about AM...
without a solid carrier at no modulation. That's exactly what mode I'm running. With my amplifier being able to key on a multiplexed signal from my radio... The DSB-SC mode really is impressive on the air at high power levels. I would never go back to pure AM mode. And you already know my feelings about SSB... it's got too many negatives for my liking. www.telstar-electronics.com |
DSB SC Mode
On a sunny day (11 Jun 2006 16:51:31 -0700) it happened "Telstar Electronics"
wrote in .com: I looked at your document. It's exactly what I'm talking about AM... without a solid carrier at no modulation. That's exactly what mode I'm running. With my amplifier being able to key on a multiplexed signal from my radio... The DSB-SC mode really is impressive on the air at high power levels. I would never go back to pure AM mode. And you already know my feelings about SSB... it's got too many negatives for my liking. www.telstar-electronics.com Hmmm does not clear up confusion, do you receive it with an AM receiver and no BFO? Then it is no DSB-SC. There exist AM modulation modes where the carrier is somewhat reduced during low modulation levels..... This wil lwork, but is still AM. Maybe that is what you mean? You will note the 'double phase rectifier' like waveform for DBS-SC. In case of that modified AM you have sine wave. So: if you can receive it on an AM receiver without BFO it is AM or a variant there of. If you need a BFO in any way it is DSB-SC, SSB, LSB, USB whatever. As far as range is concerned, SSB DSB will beat any system (with SSB being better then DSB). The variable carrier level AM, if used to give some 'extra' power to the AM stage at high amplitudes, will give some extra rane. however for weak passages in the audio there will be more noise then a similar AM system with noraml carrier, as simply there will be less carrier output. Some AM broadcast statons, if not all? Use that system. But who knows HiFi these days.. mp3... low bitrates... |
DSB SC Mode
I guess you're right. In the strictest sense DSB-SC, there is no
transmission of the carrier at all. That is not the mode I'm talking about. I guess I was using DSB-SC interchangably with the mode where the carrier is only temporarily supressed. I would certainly not be interested in the mode where the carrier is no longer transmitted... for the same reason I don't like like the SSB mode... mainly the constant fussing over the tuning. Thanks for the correction... www.telstar-electronics.com |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 13:13:42 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.13.13.40.351000@Quetzalcoatl: On Sun, 11 Jun 2006 14:38:54 +0000, Jan Panteltje wrote: Something wrong here, DSB-SC received on a normal set can only be made 'inteligible' if it is received as SSB. SSB is simply one sideband of the 2 DSB sends, so your BFO is [just as] critical. DSB-SC can be received by an ordinary AM detector, no BFO required. The two sidebands work with one another to provide the entirety of the signal so there is no garble effect as encountered when one of the sidebands is suppressed. Bull****. |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 15:09:45 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.15.09.44.566000@Quetzalcoatl: On Mon, 12 Jun 2006 14:11:03 +0000, Jan Panteltje wrote: Bull****. Is that your concise description of coherent detection? Bet you do not know what 'coherent detection' is. because if you did, you would not have written that. Ok, now rent a brain for a day, and thinks. *IF you have an AM receiver, and set the transmitetr carrier to zero, as in the case of DSB-SC with no modulation (= silence remember), then what WOULD you hear? I will tell you: All the noise in the band. Not good for silence, specially if good conditions exist! So you could have figured that out if you had been created with a brain. Also, you did not bother to look up the waveform, you just write some bull, never even designed a DSB-SC transmitter, much less ever used one. No this is perhaps not a politically correct answer, but hopefully you wil lread those papers, gooogle DVB-SC, and learn something, and then stop spreading dis-information. |
DSB SC Mode
Hmmm... that's what I thought originally. Now I'm getting confused. I'm
real interested how this discussion shakes out... www.telstar-electronics.com DSB-SC can be received by an ordinary AM detector, no BFO required. The two sidebands work with one another to provide the entirety of the signal so there is no garble effect as encountered when one of the sidebands is suppressed. In SSB the BFO supplies the missing side's opposite phase and because it's local and not sent with the signal is why it's precise tuning (or phase relationship) is critical. |
DSB SC Mode
On a sunny day (12 Jun 2006 11:20:24 -0700) it happened "Telstar Electronics"
wrote in .com: Hmmm... that's what I thought originally. Now I'm getting confused. I'm real interested how this discussion shakes out... Do not listen to him, it is 100% nonsense. Very simply: An AM detector is an 'enveloppe' detector, a DSB and SSB detector is a 'product detector'. You have seen that waveform I pointed out in fig 4 for a sine wave single tone modulation, the amplitude of the RF signal dos not really look like a sinewave does it? So you hear sever distortion, in fact you cannot make out what it is. In a product detector the BFO is the 'substitute' carrier, and multiplication of one (SSB) or both (DSB) sideband[s] gives the original modulation. There is in fact no need for the 'other' sideband in DSB-SC, no problem if the receiver filters it out, that is why you can receive DSB-SC both with USB and LSB! But for the non-believers, try it out, all you need is an audio amp, oscillator, 4 diodes, and of course a 27 HHz xtal oscillator. http://www.nzart.org.nz/nzart/examin...les/Mixers.htm There is a description and diagram a bit down on the page. Listen to it on an AM receiver, and you will KNOW. |
DSB SC Mode
On Sun, 11 Jun 2006 14:38:54 GMT, Jan Panteltje
wrote: +++Something wrong here, DSB-SC received on a normal set can only be +++made 'inteligible' if it is received as SSB. +++SSB is simply one sideband of the 2 DSB sends, so your BFO is [just as] +++critical. +++If you BFO is of center (so you re-insert the wrong carrier) and your RX +++filter already removed the other sideband, then you have all the 'duck' +++sound of SSB. +++Moderns CB sets have no 'DSB' option, only USB / LSB, so always use one +++sideband. +++In case a set DOES pass both sideband, you get double the problem.... +++ +++Maybe you mean something else by DSB-SC altogether? Leave SOME carrier? ************************** DSB-SC reception is not restricted to just SSB-SC receivers. A DSB-SC signal can be received by reinjecting the carrier, even on a DSB receiver. DSB-SC stands for Double Sideband Supressed Carrier. james |
DSB SC Mode
On Sun, 11 Jun 2006 21:16:28 GMT, Jan Panteltje
wrote: +++On a sunny day (11 Jun 2006 13:35:21 -0700) it happened "Telstar Electronics" wrote in oups.com: +++ +++Not sure what you're talking about. When I say DSB... I'm referring to +++what others call the AM mode. +++ +++www.telstar-electronics.com +++ +++ +++DSB-SC (as you originally referred to) stands for: +++Double Sideband Suppressed Carrier. +++So, if the carrier is surpressed, then you have only 2 sidebands if a signal +++is present (single tone modulation), nothing if no modulation is present. +++ http://www.ece.drexel.edu/courses/ECE-S306/lab3.pdf +++Look at figure 4, for a single tone modulating audio signal. +++You will notice it is quite different from AM! +++ +++Normal AM is also DSB, but the carrier is not surpressed. +++Better to say AM if you mean AM, DSB is often used for DSB-SC. ______________ AM == Double Sideband Full Carrier. james |
DSB SC Mode
"Telstar Electronics" wrote in message
oups.com... So let me get this straight... In DSB-SC... both sidebands are transmitted... but there is no carrier sent at all? Correct?... and the carrier is re-inserted at the receiver. Now with the swing set-up... both sidebands are transmitted... along with the carrier... but the carrier's amplitude changes from extremely low to a normal AM carrier when the modulation is added. www.telstar-electronics.com There is no carrier. It's like listening to LSB and USB at the same time. If you remove half the ssb signal, say LSB, you would hear more of the donald duck sound due to the reduced size of the bandwidth. Just forget AM carrier when talking DSB-SC as it just isn't there. DSB is AM and when the carrier is removed you have DSB-SC |
DSB SC Mode
On Mon, 12 Jun 2006 18:34:51 GMT, Jan Panteltje
wrote: +++On a sunny day (12 Jun 2006 11:20:24 -0700) it happened "Telstar Electronics" wrote in oups.com: +++ +++Hmmm... that's what I thought originally. Now I'm getting confused. I'm +++real interested how this discussion shakes out... +++ +++Do not listen to him, it is 100% nonsense. +++ +++Very simply: +++An AM detector is an 'enveloppe' detector, +++a DSB and SSB detector is a 'product detector'. ***** A product Detector is prefered due to its mixer characteristics. Being balanced, the two inputs are supressed sufficiently to make filtering their components in the output much easier. Product detectors and Envelope dection is not the only means of detecting DSB-SC and DSB-LC signals. They are the most simplest and easiest to implement. +++ +++You have seen that waveform I pointed out in fig 4 for a sine wave single +++tone modulation, the amplitude of the RF signal dos not really look like a +++sinewave does it? +++ +++So you hear sever distortion, in fact you cannot make out what it is. +++ ***** Distortion of the RF waveform may not nescessarily indicate that the detected audio is unintelligable. As long as the recovered audio is reproduced accuarately during demodulation then there is no distortion. Spectral content of the demodualted signal can be set by post detection filtering. This can reduce to some extent the harmonics of the modulating signal. By the way the lab you point to is more about the generation of a DSB signal. From figure 4 you are making statements about demodulation. +++In a product detector the BFO is the 'substitute' carrier, and multiplication +++of one (SSB) or both (DSB) sideband[s] gives the original modulation. +++ +++There is in fact no need for the 'other' sideband in DSB-SC, no problem if +++the receiver filters it out, that is why you can receive DSB-SC both with +++USB and LSB! +++ *********** Since the information in both sidebands are indentical the only need for the second sideband is to increase demodulated audio. +++But for the non-believers, try it out, all you need is an audio amp, +++oscillator, 4 diodes, and of course a 27 HHz xtal oscillator. +++http://www.nzart.org.nz/nzart/examin...les/Mixers.htm +++ +++There is a description and diagram a bit down on the page. +++ +++Listen to it on an AM receiver, and you will KNOW. +++ james |
DSB SC Mode
On 12 Jun 2006 13:42:26 -0700, "Telstar Electronics"
wrote: +++So let me get this straight... In DSB-SC... both sidebands are +++transmitted... but there is no carrier sent at all? Correct?... and the +++carrier is re-inserted at the receiver. +++ ************* Not exactly. Supressed carrier is just that. The carrier is suppressed by a desired amount measured in dBs. It can be fully suppressed or partially supressed. +++Now with the swing set-up... both sidebands are transmitted... along +++with the carrier... but the carrier's amplitude changes from extremely +++low to a normal AM carrier when the modulation is added. +++ ************* There is several techniques that has been used in amatuer radio for many decades. One stems from the old tube days called grid modulation. What happens here is that the modulated stage, usually the final RF stage, has the modulation signal applied to the grid of the tube. By varying the grid voltage at an audio rate, the bias on the tube varies. This will change the gain of the tube. What happens then is when there is no modulation signal the tube is at or near cutoff and there is little carrier. As you modulate the carrier varies at an audio rate. Disadvantage of this method is the maximum percentage of modulation is about 85%. Another method is one sed by the Drake 4 line series of transmitters. This is where modulation is applied to a low level stage. Usually a balanced modulator. To achieve AM, the balanced modulator is slightly kicked off balanced to allow a small amount of carrier to appear at the output. With modualtion this will vary some. Subsequent stages of amplification will bring the signal up to the desired level. james |
DSB SC Mode
On Mon, 12 Jun 2006 23:50:21 GMT, Bob Dobbs EC42
wrote: +++On Mon, 12 Jun 2006 16:17:21 -0500, DrDeath wrote: +++ +++ There is no carrier. +++ +++No Carrier - no propagation ****************** You have to remember that in DSB-SC and in SSB tranmission the audio, modulating signal, spectrum is mixed up to the desire frequency range. In these voice signals the audio is now moved u p in the frequency spectrum. That is essentially what modulation does, frequency transform. In both DSB-SC and SSB, your are now transmitting a band of frequencies that is equaly to the voice bandwidth at varying power densities. In DSB-LC, the carrier goes along for the ride to demodulate the signals at the receiver. The carrier does not carry ant information at all. james |
DSB SC Mode
Telstar Electronics wrote: Hmmm... that's what I thought originally. Now I'm getting confused. I'm real interested how this discussion shakes out... www.telstar-electronics.com indeed a something close to a flamefest of a what to call mode oh well at least it is a reasonably on topic post for once personaly I like basci AM well enough although I use SSB on cb since I can't legaly boost the power level but in ham bands I love AM better |
DSB SC Mode
Yes... at least the discussion is something interesting... instead of
dougie this and dougie that... whoever dougie is... LOL I still trying to research this topic.... since there seems to be considerably different views of DSB-SC out here. I'm starting to think my original statement that a very high swing AM transmission can be considered a DSB-SC... and requires no special BFO tuning. www.telstar-electronics.com |
DSB SC Mode
"Telstar Electronics" wrote in message
oups.com... Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL I still trying to research this topic.... since there seems to be considerably different views of DSB-SC out here. I'm starting to think my original statement that a very high swing AM transmission can be considered a DSB-SC... and requires no special BFO tuning. www.telstar-electronics.com Nope, if you listen with your rig set to AM and the transmission is DSB-SC you will hear a garbled mess. If you set both rigs to AM and lower the deadkey to say an 1/8 watt with 15 watts of swing you can understand the low dead key rig. |
DSB SC Mode
"Telstar Electronics" wrote:
Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL Here's who dogie is. (like you didn't know, griffey) http://n8wwm.4t.com/photo.html |
DSB SC Mode
"Steveo" wrote in message
... "Telstar Electronics" wrote: Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL Here's who dogie is. (like you didn't know, griffey) http://n8wwm.4t.com/photo.html He's been here long enough to know. The question is whether he is playing stupid or just plain stupid. |
DSB SC Mode
"Telstar Electronics" wrote in message
oups.com... Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL I still trying to research this topic.... since there seems to be considerably different views of DSB-SC out here. I'm starting to think my original statement that a very high swing AM transmission can be considered a DSB-SC... and requires no special BFO tuning. www.telstar-electronics.com I agree that we finally have a topic worth discussing. The sad part is you call yourself a professor, and design and build amps, leading one to believe you know about radio, yet are having a tough time grasping the DSB-SC theory |
DSB SC Mode
"DrDeath" wrote:
"Steveo" wrote in message ... "Telstar Electronics" wrote: Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL Here's who dogie is. (like you didn't know, griffey) http://n8wwm.4t.com/photo.html He's been here long enough to know. The question is whether he is playing stupid or just plain stupid. He's been kissing up to him for years..ask anyone that would know. They've both have an angle to sell something, and there's nothing wrong with that as long as you're careful who you are in business with. |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 20:22:15 GMT) it happened james
wrote in : On Sun, 11 Jun 2006 14:38:54 GMT, Jan Panteltje wrote: +++Something wrong here, DSB-SC received on a normal set can only be +++made 'inteligible' if it is received as SSB. +++SSB is simply one sideband of the 2 DSB sends, so your BFO is [just as] +++critical. +++If you BFO is of center (so you re-insert the wrong carrier) and your RX +++filter already removed the other sideband, then you have all the 'duck' +++sound of SSB. +++Moderns CB sets have no 'DSB' option, only USB / LSB, so always use one +++sideband. +++In case a set DOES pass both sideband, you get double the problem.... +++ +++Maybe you mean something else by DSB-SC altogether? Leave SOME carrier? ************************** DSB-SC reception is not restricted to just SSB-SC receivers. A DSB-SC signal can be received by reinjecting the carrier, even on a DSB receiver. It can be received even on an AM receiver if you feed in a local oscillator at fc, I have done this, so what is your point? |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 23:19:21 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.19.18.864000@Quetzalcoatl: On Mon, 12 Jun 2006 15:28:30 +0000, Jan Panteltje wrote: snipped the cerebral cesspool No this is perhaps not a politically correct answer, but hopefully you wil lread those papers, gooogle DVB-SC, and learn something, and then stop spreading dis-information. OK Here's what your learned suggestion yielded; http://tinyurl.com/g7wy6 I have to admit the results exceeded my ability to correlate them to the topic of discussion, so I guess you win by virtue of posting sufficient arcane bull**** to shock and awe me into submission. ;-) idiot. |
DSB SC Mode
On a sunny day (Tue, 13 Jun 2006 00:32:38 GMT) it happened james
wrote in : A product Detector is prefered due to its mixer characteristics. Being balanced, the two inputs are supressed sufficiently to make filtering their components in the output much easier. Product detectors and Envelope dection is not the only means of detecting DSB-SC and DSB-LC signals. They are the most simplest and easiest to implement. I have used sampling to demodulate QAM, In any color TV you will find it, carrier is regenerated in phase from the color burst, look up NTSC. And there we have 2 modulating systems, here is how that works in the time domain: http://groups.google.com/group/sci.e...ce23fcbb253646 The main thing is perhaps that you can see that in SSB, if we have 1MHz carrier, and 1kHz sine modulation, we get a 1.001 MHz carrier (or 0.999 if the other sideband is used. So to get the original back, it would be sufficient to substract the 1MHz again in the first case (1.001 - 1) = 1kHz, or in the other case 1 - .999. In the DSB-SC case we would have 1.001 AND .999 AT THE SAME TIME. Using one sideband is enough. DSB uses double the bandwidth and as such is less efficient then SSB, Distortion of the RF waveform may not nescessarily indicate that the detected audio is unintelligable. As long as the recovered audio is reproduced accuarately during demodulation then there is no distortion. But it won't [work]. What the 4 diode ring modulator does, is make a RF amplitude phase phi when the audio signal goes positive proportional to the audio amplitude, and the same with phase phi+180 degrees when the audio signal goes negative. If you do AM envelope detector (as the you normally do with a diode and RC lowpass) you get a wave form that is no longer a sine, but looks like double phase rectified sine when filtered. Spectral content of the demodualted signal can be set by post detection filtering. This can reduce to some extent the harmonics of the modulating signal. By the way the lab you point to is more about the generation of a DSB signal. From figure 4 you are making statements about demodulation. Of course, lok at that waveform, build a 'non distorting AM detector for it without carrier re-insertion (BFO, some oscillator), you CANNOT. Modulation /demodulation is related. Please build one, try it, Since the information in both sidebands are indentical the only need for the second sideband is to increase demodulated audio. Yes, we agree here. Please try it: But for the non-believers, try it out, all you need is an audio amp, oscillator, 4 diodes, and of course a 27 HHz xtal oscillator. http://www.nzart.org.nz/nzart/examin...les/Mixers.htm There is a description and diagram a bit down on the page. Listen to it on an AM receiver, and you will KNOW. |
DSB SC Mode
On a sunny day (12 Jun 2006 13:42:26 -0700) it happened "Telstar Electronics"
wrote in .com: So let me get this straight... In DSB-SC... both sidebands are transmitted... but there is no carrier sent at all? Correct?... and the carrier is re-inserted at the receiver. 100% correct. Now with the swing set-up... both sidebands are transmitted... along with the carrier... but the carrier's amplitude changes from extremely low to a normal AM carrier when the modulation is added. right again. www.telstar-electronics.com |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 23:22:52 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.22.49.949000@Quetzalcoatl: On Mon, 12 Jun 2006 11:20:24 -0700, Telstar Electronics wrote: Hmmm... that's what I thought originally. Now I'm getting confused. I'm real interested how this discussion shakes out... Yeah, me too. I'm hoping that Panteltje dude can get over his constipation and offer something more enlightening than the flatulence blowing from his keyboard. idiot |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 23:34:57 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.34.54.717000@Quetzalcoatl: On Mon, 12 Jun 2006 18:34:51 +0000, Jan Panteltje wrote: There is in fact no need for the 'other' sideband in DSB-SC, no problem if the receiver filters it out, that is why you can receive DSB-SC both with USB and LSB! Without both sidebands, it would no longer be DSB, and the reason stations use DSB instead of SSB is for the use of ordinary receivers that lack a BFO. How about providing a source of those 'undetectable" DSBSC signals that one might encounter within or nearby to the CB band, instead of some technobabble with irrelevant circuitry illustrations? OK for the last time before you enter my killfile: DSB is not AM. AM is AM, and AM has both sidebands, but when we say 'DSB we mean DSB-SC. idiot |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 23:42:59 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.42.57.909000@Quetzalcoatl: On Mon, 12 Jun 2006 13:42:26 -0700, Telstar Electronics wrote: So let me get this straight... In DSB-SC... both sidebands are transmitted... but there is no carrier sent at all? Correct?... and the carrier is re-inserted at the receiver. That's what Panteltje would have you believe. Without a carrier there would be no RF propagation. Now with the swing set-up... both sidebands are transmitted... along with the carrier... but the carrier's amplitude changes from extremely low to a normal AM carrier when the modulation is added. That's right, the supressed carrier becomes un-supressed according to the amplitude of the Modulation, otherwise there wouldn't be a signal. IOW: Supress the carrier out entirely and all you have is audio, no radio propagation, have to shout real loud to get any DX out of that. Sorry dude, the sidebands are RF. |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 23:50:21 GMT) it happened Bob Dobbs EC42
wrote in pan.2006.06.12.23.50.19.219000@Quetzalcoatl: On Mon, 12 Jun 2006 16:17:21 -0500, DrDeath wrote: There is no carrier. No Carrier - no propagation It's like listening to LSB and USB at the same time. That's what an AM receiver does. If you remove half the ssb signal, say LSB, you would hear more of the donald duck sound due to the reduced size of the bandwidth. Not bandwidth reduction, but the lacy of waveform symetry Just forget AM carrier when talking DSB-SC as it just isn't there. DSB is AM and when the carrier is removed you have DSB-SC As I've tried to point out with out a carrier there isn't propagation. why do you think they call it "supressed" carrier Because it ain't there anymore, just like in SSB. instead of removed carrier? Because they already used 'removed' for brain. |
DSB SC Mode
On a sunny day (Tue, 13 Jun 2006 00:44:15 GMT) it happened james
wrote in : On 12 Jun 2006 13:42:26 -0700, "Telstar Electronics" wrote: +++So let me get this straight... In DSB-SC... both sidebands are +++transmitted... but there is no carrier sent at all? Correct?... and the +++carrier is re-inserted at the receiver. +++ ************* Not exactly. Supressed carrier is just that. The carrier is suppressed by a desired amount measured in dBs. It can be fully suppressed or partially supressed. +++Now with the swing set-up... both sidebands are transmitted... along +++with the carrier... but the carrier's amplitude changes from extremely +++low to a normal AM carrier when the modulation is added. +++ ************* There is several techniques that has been used in amatuer radio for many decades. One stems from the old tube days called grid modulation. What happens here is that the modulated stage, usually the final RF stage, has the modulation signal applied to the grid of the tube. By varying the grid voltage at an audio rate, the bias on the tube varies. This will change the gain of the tube. What happens then is when there is no modulation signal the tube is at or near cutoff and there is little carrier. As you modulate the carrier varies at an audio rate. Disadvantage of this method is the maximum percentage of modulation is about 85%. Another method is one sed by the Drake 4 line series of transmitters. This is where modulation is applied to a low level stage. Usually a balanced modulator. To achieve AM, the balanced modulator is slightly kicked off balanced to allow a small amount of carrier to appear at the output. With modualtion this will vary some. Subsequent stages of amplification will bring the signal up to the desired level. james 100% agreed. |
DSB SC Mode
On a sunny day (Mon, 12 Jun 2006 21:01:33 -0500) it happened "DrDeath"
wrote in : "Telstar Electronics" wrote in message roups.com... Yes... at least the discussion is something interesting... instead of dougie this and dougie that... whoever dougie is... LOL I still trying to research this topic.... since there seems to be considerably different views of DSB-SC out here. I'm starting to think my original statement that a very high swing AM transmission can be considered a DSB-SC... and requires no special BFO tuning. www.telstar-electronics.com Nope, if you listen with your rig set to AM and the transmission is DSB-SC you will hear a garbled mess. Exactly! |
DSB SC Mode
I thought this was very helpful for me.
http://www.williamson-labs.com/480_dsb.htm It shows that in DSB-SC... both sidebands are transmitted (they are RF) and that no carrier is ever transmitted. The carrier would have to be added back at the receiver. I believe that would have the same critical tuning issues as SSB. I'm not sure why anyone would want to do this as all the intelligence is contained in a single sideband anyway. So it appears that DSB-SC is not much different than SSB-SC. I guess that really figured. I was wrong in using DSB-SC and a mode that is basically AM (with a greatly reduced carrier that increases via modulation) interchangeably. It now is apparent they are not the same. www.telstar-electronics.com |
DSB SC Mode
Jan
I don't have to go through your exercises, I am very well familiar with diode ring demodulators and various other techniques to demodulate audio in amplitude modualted sysytems. I am well aware of the trade offs in effectiveness and costs of may different aprroaches. james On Tue, 13 Jun 2006 10:15:08 GMT, Jan Panteltje wrote: +++On a sunny day (Tue, 13 Jun 2006 00:32:38 GMT) it happened james wrote in : +++ +++A product Detector is prefered due to its mixer characteristics. Being +++balanced, the two inputs are supressed sufficiently to make filtering +++their components in the output much easier. Product detectors and +++Envelope dection is not the only means of detecting DSB-SC and DSB-LC +++signals. They are the most simplest and easiest to implement. +++ +++I have used sampling to demodulate QAM, In any color TV you will find it, +++carrier is regenerated in phase from the color burst, look up NTSC. +++And there we have 2 modulating systems, here is how that works in the +++time domain: +++ http://groups.google.com/group/sci.e...ce23fcbb253646 +++ +++The main thing is perhaps that you can see that in SSB, if we have 1MHz +++carrier, and 1kHz sine modulation, we get a 1.001 MHz carrier (or 0.999 if +++the other sideband is used. +++So to get the original back, it would be sufficient to substract the 1MHz +++again in the first case (1.001 - 1) = 1kHz, or in the other case 1 - .999. +++ +++In the DSB-SC case we would have 1.001 AND .999 AT THE SAME TIME. +++ +++Using one sideband is enough. DSB uses double the bandwidth and as such +++is less efficient then SSB, +++ +++Distortion of the RF waveform may not nescessarily indicate that the +++detected audio is unintelligable. As long as the recovered audio is +++reproduced accuarately during demodulation then there is no +++distortion. +++ +++But it won't [work]. +++What the 4 diode ring modulator does, is make a RF amplitude phase phi +++when the audio signal goes positive proportional to the audio amplitude, +++and the same with phase phi+180 degrees when the audio signal goes negative. +++If you do AM envelope detector (as the you normally do with a diode and RC +++lowpass) you get a wave form that is no longer a sine, but looks like double +++phase rectified sine when filtered. +++ +++ +++ Spectral content of the demodualted signal can be set by +++post detection filtering. This can reduce to some extent the harmonics +++of the modulating signal. +++ +++ +++ +++By the way the lab you point to is more about the generation of a DSB +++signal. From figure 4 you are making statements about demodulation. +++ +++Of course, lok at that waveform, build a 'non distorting AM detector +++for it without carrier re-insertion (BFO, some oscillator), you CANNOT. +++Modulation /demodulation is related. +++ +++Please build one, try it, +++ +++Since the information in both sidebands are indentical the only need +++for the second sideband is to increase demodulated audio. +++ +++Yes, we agree here. +++ +++Please try it: +++ +++But for the non-believers, try it out, all you need is an audio amp, +++oscillator, 4 diodes, and of course a 27 HHz xtal oscillator. +++http://www.nzart.org.nz/nzart/examin...les/Mixers.htm +++There is a description and diagram a bit down on the page. +++ +++Listen to it on an AM receiver, and you will KNOW. +++ |
DSB SC Mode
On Tue, 13 Jun 2006 10:18:17 GMT, Jan Panteltje
wrote: +++On a sunny day (Mon, 12 Jun 2006 23:34:57 GMT) it happened Bob Dobbs EC42 wrote in pan.2006.06.12.23.34.54.717000@Quetzalcoatl: +++ +++On Mon, 12 Jun 2006 18:34:51 +0000, Jan Panteltje wrote: +++ +++ There is in fact no need for the 'other' sideband in DSB-SC, no problem +++ if the receiver filters it out, that is why you can receive DSB-SC both +++ with USB and LSB! +++ +++Without both sidebands, it would no longer be DSB, and the reason stations +++use DSB instead of SSB is for the use of ordinary receivers that lack a +++BFO. +++ +++How about providing a source of those 'undetectable" DSBSC signals that +++one might encounter within or nearby to the CB band, instead of some +++technobabble with irrelevant circuitry illustrations? +++ +++OK for the last time before you enter my killfile: +++DSB is not AM. AM is AM, and AM has both sidebands, but when we say 'DSB we mean DSB-SC. +++idiot +++ +++ +++ +++ ************************** We seem to be hung up on abbreviations and their applications to analog communications. A list of Abbreviation in analog Modulation from Introduction to Communications System Third Edition by Ferrel G. Stremler. This is taken from my Communications Textbook from college. 1)AM AMplitude Modulation: A CW modulation using amplitude variation in proportion to the amplitude of the modulating signal. Usually taken as DSB-LC for commercial broadcast transmission and DSB-SC for multiplexed systemes. 2) CW COntinuous Wave: A carrier signal (usually sinusoidal) used for modulation or keying. 3) DSB Double Sideband(LC or SC): a signal having two spectral sidebands symetrically balanced with respect tothe carrier frequency. 4) LC Large Carrier: a signal in which a relatively large proprotion of the spectrum is concentrated at the carrier frequency ( used with DSB, SSB, and VSB). 5) SC Supressed Carrier: a signal in which a relatively small proportion (ideally zero) of the spectrum is is concentrated at the carier frequency ( used with DSB, SSB, VSB). Now translating into CB lingo AM and DSB-LC are synonymous. That is what nearly all off the shelf AM CB radios produce. Modulation takes place in the final stage before the antenna. There are some that use low level modulation that follow the modulated stage with further amplification afterwards to raise the power density to a level to effect the desired communication range with the intended antenna system. Please note that the difference between Large Carrier and Suppressed carrier can be used with DSB, SSB and VSB amplitude systems. The difference is the role the carrier itself plays in demodulaztion ONLY! In DSB it is generally accepted that both sidebands carry the same information during modualation. SSB is defined as a spectrum in which only one sideband is trransmitted with or without the carrier. Vestigial Sideband is where one full sideband is and a partial of the other sideband is not fully transmitted. TV signals are VSB signals. hope this helps james |
DSB SC Mode
"Jan Panteltje" wrote in message ... I did a nice frequency counter on an FPGA lab board: http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2 And just how do you open/view such a beast? WinRAR opened the file, but left me with another file that was unknown and completely useless... If you are trying to make a point, you might want to put it in a format that humans can actually use... |
DSB SC Mode
PowerHouse Communications schreef: "Jan Panteltje" wrote in message ... I did a nice frequency counter on an FPGA lab board: http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2 And just how do you open/view such a beast? WinRAR opened the file, but left me with another file that was unknown and completely useless... If you are trying to make a point, you might want to put it in a format that humans can actually use... 'bz2' is a compressed format, it is open source, and frequently used in Linux. It has a higher compression ratio then for exmpel 'zip' or tgz. the correct way to 'unpack' it in Linux / unix is: tar -jxvf frequency_counter-0.2.1.bz2 In MS windows there is as far as i knwo no correct way to do anything, so I cannot help you there. You would only find verilog source files anyways, and then complain you cannot read verilog (language), that posting really was on level3, you were still on level 1. |
DSB SC Mode
wrote in message
oups.com... PowerHouse Communications schreef: "Jan Panteltje" wrote in message ... I did a nice frequency counter on an FPGA lab board: http://panteltje.com/panteltje/fpga/...nter-0.2.1.bz2 And just how do you open/view such a beast? WinRAR opened the file, but left me with another file that was unknown and completely useless... If you are trying to make a point, you might want to put it in a format that humans can actually use... 'bz2' is a compressed format, it is open source, and frequently used in Linux. It has a higher compression ratio then for exmpel 'zip' or tgz. the correct way to 'unpack' it in Linux / unix is: tar -jxvf frequency_counter-0.2.1.bz2 In MS windows there is as far as i knwo no correct way to do anything, so I cannot help you there. Like I told you, WinRAR opened (uncompressed) the file (unpack[ed] it in your language)... You would only find verilog source files anyways, and then complain you cannot read verilog (language), that posting really was on level3, you were still on level 1. I could really give a **** less what planet you are on, I asked a simple question, all you had to do was answer it without your nasty attitude. It was nice of you to provide a link, however I'd roughly guess that over 98% of the people reading this group, including the person you replied to, does not use Linux, and therefore would have no use for the file. Oh, and since you have a cocky attitude about you, let me return the favor... IT'S "example", NOT "exmpel"! |
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