RE: [AMRadio] Physical Reality of Sidebands
Yep, I know Larry, but I had already gotten deeper than I intended to. Because most of the video is motionless, the sidebands come out at multiples of the sweep rate. The color sub carrier frequency which is only transmitted in burst mode as previously describe, was chosen at the odd frequency that it is, so that in spectrum, most of the sideband energy containing the color info, would fall between the energy of the black and white info. This was in hope of having less "intermodulation" at the detector. As for I know, it was not until Magnavox produced the first COMB FILTER that we were able to make use of this bit of spectrum conservation. It is interesting to note that the color sidebands were 500KHz of upper and lower sideband spectrum except at the phase difference of around 80-100 deg where the flesh tones are produced and at that phase difference the band width is much greater but only on one sideband. The RCA CTC 4 chassis made use of this with the "I and Q" demodulation system, a very difficult sweep / band pass alignment procedure. This is all getting off the subject, but it was interesting to me that all this could be kept separate with the fast switching on and off of the burst and changing bandwidth of the I and Q modulated signal. I love all this type of discussion. I am afraid I would have to lean towards the theory, that it is what ever fits the need of the detector. At what wavelength does Electro-magnetic radiation become a particle? Is the Universe homogeneous or chaotic? That depends upon how it is observed. John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Monday, January 17, 2005 2:40 PM To: Discussion of AM Radio Subject: RE: [AMRadio] Physical Reality of Sidebands John, You are close. That was the old black and white days. Since color its divided down from 3.579454 to 15, 726.xx (approx) and vertical is 59,94 not 60.00. Larry W3LW On Sun, 16 Jan 2005 22:58:04 -0600, "John Coleman ARS WA5BXO" <[EMAIL PROTECTED]> wrote : > > Don, I have often pondered the same thing here is another example. > > The Horizontal sweep rate of a TV is 15750 hz. Every 1/15000 of > a sec there is a sync pedestal, and on the back porch of it is a burst > of a few cycles (as I remember it was 8 to 10 cycles in length) of the > color sub carrier (3.579545 MHz). This burst is removed and processed > by an amplifier that is key on by the horizontal retrace pulse which has > been synced to the horizontal sync pulse that rides atop the sync > pedestal just in front of the color burst. The 8 cycle color burst is > phase compared to a crystal oscillator in a phase locked loop. A good > synchronized scope can look at the full video detected signal and spread > the back porch of the sync pedestal out and view the 8-10 cycles of the > burst. I often wondered what a spectrum analyzer would look like when > monitoring the output of the burst amplifier with the phase detector > diodes remove. > > The burst amplifier was a simple tetrode whose plate circuit had > a parallel tank tuned to 3.58 MHZ and where the detected video was > applied to the grid through a small coupling capacitor that would > differentiate and pass the frequencies higher than 3 MHz. The grid leak > was returned to a circuit where a positive pulse from the fly back was > present to trigger the tube on. The output tank was link coupled to the > phase detector. > > > John, > WA5BXO > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > > > __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net
RE: [AMRadio] Physical Reality of Sidebands
An interesting aside is that burst is a shade of green, and appears a somewhat sickly green at that. >The 8 cycle color burst is phase compared to a crystal oscillator in a phase locked loop.
RE: [AMRadio] Physical Reality of Sidebands
John, You are close. That was the old black and white days. Since color its divided down from 3.579454 to 15, 726.xx (approx) and vertical is 59,94 not 60.00. Larry W3LW On Sun, 16 Jan 2005 22:58:04 -0600, "John Coleman ARS WA5BXO" <[EMAIL PROTECTED]> wrote : > > Don, I have often pondered the same thing here is another example. > > The Horizontal sweep rate of a TV is 15750 hz. Every 1/15000 of > a sec there is a sync pedestal, and on the back porch of it is a burst > of a few cycles (as I remember it was 8 to 10 cycles in length) of the > color sub carrier (3.579545 MHz). This burst is removed and processed > by an amplifier that is key on by the horizontal retrace pulse which has > been synced to the horizontal sync pulse that rides atop the sync > pedestal just in front of the color burst. The 8 cycle color burst is > phase compared to a crystal oscillator in a phase locked loop. A good > synchronized scope can look at the full video detected signal and spread > the back porch of the sync pedestal out and view the 8-10 cycles of the > burst. I often wondered what a spectrum analyzer would look like when > monitoring the output of the burst amplifier with the phase detector > diodes remove. > > The burst amplifier was a simple tetrode whose plate circuit had > a parallel tank tuned to 3.58 MHZ and where the detected video was > applied to the grid through a small coupling capacitor that would > differentiate and pass the frequencies higher than 3 MHz. The grid leak > was returned to a circuit where a positive pulse from the fly back was > present to trigger the tube on. The output tank was link coupled to the > phase detector. > > > John, > WA5BXO > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > > >
Re: [AMRadio] Physical Reality of Sidebands
Bob, You are correct. If I was home I'd send along the basic formula for modulation. In FLA right now on vacation. It is multiplication just as a mixer is (the formula is the same really). All AM modulation and demodulation is multiplication but in vector notation. Check any college text on information theory. regards, Larry W3LW On Mon, 17 Jan 2005 14:17:54 -0500, "Bob Bruhns" <[EMAIL PROTECTED]> wrote : > Hi Gary, > > The carrier is not multiplied with the sideband frequencies to > generate AM, it is multiplied with the baseband modulating > frequency. In my example, three sine waves corresponding to a > carrier and two sideband frequencies are added together to produce > the AM signal, but a relatively low frequency is multiplied with the > carrier in the AM transmitter to produce the carrier and sideband > frequencies in the reverse example. Interestingly, if the AM > signal, with or without carrier, is multiplied at the receiver with > a regenerated carrier of proper frequency and phase, then the > baseband modulating signal is recovered. > > In the transmitter, the multiplication occurs in the modulated > stage. In plate-modulated AM, the carrier is multiplied by the > plate voltage. Normalizing plate voltage to unity, it is multiplied > by +1 without modulation. Modulation varies the B+, and therefore > the multiplication factor. The normalized multiplication factor > varies from 0 to +2 with 100% sine wave modulation. > > Bacon, WA3WDR > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > > >
Re: [AMRadio] Physical Reality of Sidebands
Hi Gary, The carrier is not multiplied with the sideband frequencies to generate AM, it is multiplied with the baseband modulating frequency. In my example, three sine waves corresponding to a carrier and two sideband frequencies are added together to produce the AM signal, but a relatively low frequency is multiplied with the carrier in the AM transmitter to produce the carrier and sideband frequencies in the reverse example. Interestingly, if the AM signal, with or without carrier, is multiplied at the receiver with a regenerated carrier of proper frequency and phase, then the baseband modulating signal is recovered. In the transmitter, the multiplication occurs in the modulated stage. In plate-modulated AM, the carrier is multiplied by the plate voltage. Normalizing plate voltage to unity, it is multiplied by +1 without modulation. Modulation varies the B+, and therefore the multiplication factor. The normalized multiplication factor varies from 0 to +2 with 100% sine wave modulation. Bacon, WA3WDR
Re: [AMRadio] Physical Reality of Sidebands
Jim Wilhite wrote: Out of curiosity Gary, where do you think the multiplication occurs? In the plate of the final(s), at the juncture of the plate and output network, or in the final network? I have pondered this one and have an opinion, but would like yours and others opinions. 73 Jim W5JO Hi Jim, I should have figured you would come up with that one. :>) In an oscillator it is really the tuned circuit that is the oscillator and the tube is just a switch that keeps the oscillation going in the tank. Same for the output tank on an amplifier. The tube is a switch that excites the tank. However with modulation you can do it with a diode and a resistor for the load so I would have to say that modulation takes place as a function of the switch action. But without the load there is no current so nothing happens. So it seems it may occur at the junction of the load and the switch? 73 Gary K4FMX
Re: [AMRadio] Physical Reality of Sidebands
Out of curiosity Gary, where do you think the multiplication occurs? In the plate of the final(s), at the juncture of the plate and output network, or in the final network? I have pondered this one and have an opinion, but would like yours and others opinions. 73 Jim W5JO - Original Message - From: "Gary Schafer" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Monday, January 17, 2005 10:01 AM Subject: Re: [AMRadio] Physical Reality of Sidebands Bob Bruhns wrote: Indeed, 'tis a puzzlement. I can draw three continuous sine waves of apppropriate amplitude, frequency and phase, corresponding to carrier, upper sideband and lower sideband, and I can add them point by point, and I can duplicate a 100% modulated AM signal waveform as we understand it. I have to believe that this works backwards; if I make this waveform by modulating a carrier in an AM transmitter, then I am synthesizing the same continuous sine waves.
Re: [AMRadio] Physical Reality of Sidebands
Bob Bruhns wrote: Indeed, 'tis a puzzlement. I can draw three continuous sine waves of apppropriate amplitude, frequency and phase, corresponding to carrier, upper sideband and lower sideband, and I can add them point by point, and I can duplicate a 100% modulated AM signal waveform as we understand it. I have to believe that this works backwards; if I make this waveform by modulating a carrier in an AM transmitter, then I am synthesizing the same continuous sine waves. Hi Bob, The three sin waves look like what is happening but in reality the am signal is not produced by adding sin waves. It is produced by multiplying them. It just happens that when you add them you come out with the same result so it appears that they are added. And to keep things simple that is how it has been taught over the years as another poster mentioned. 73 Gary K4FMX
[AMRadio] coils needed
Howdy Men I am in need of a 40jel and a 80jel coil set.. I have sockets. Even if they need repair.. anyone have any of these to part with? thanks Ronnie
Re: [AMRadio] Physical Reality of Sidebands
I am convinced that sidebands exist. But as for whether the carrier goes away at 100% negative modulation... How's this: a carrier should be considered to exist during the period when it has recently been detected, and we are actually receiving modulation from it. It should not be considered to exist when it is clearly not being generated. So in the example of an AM signal at the instant of 100% negative modulation, we should consider the zero to represent zero percent of the carrier, averaged over time during recent history. We can see that this will result in appropriate demodulation of the actual signal. But when the AM transmission is over, either after the end of a transmission, or after the end of a broadcast day, or in most cases if the signal fades out due to propagation, etc, we should consider the carrier not to be present. This gets a little tricky, because we can not really be certain (Don's Heisenberg Uncertainty Principle thought here) that the transmitter is not sending us a very, very long zero. But we can be pretty sure, pretty quick. A synchronous detector is a good flywheel that tracks the known carrier frequency and holds the reference for us during zeros and noise bursts. We set up a synchronous detector to detect the carrier and hold the reference for a short period of time. This works pretty well for the signals we actually transmit. Now take the example of a 1 KHz sinewave transmitted as double sideband suppressed carrier. You get pulses of alternating carrier polarity. During any given pulse, for about 500 microseconds at a time, you get an AM signal with a carrier, transmitting one half of a sine wave. When the pulse is over and the signal passes through zero, it goes negative and the next pulse appears - pretty much identical to the first pulse, but with reverse carrier polarity. You would not know the carrier polarity reversed except for your flywheel reference. But demodulating with the flywheel reference gives you the 1 KHz sinewave. It is evident to the observer that the flywheel reference was correct. With a very low modulating frequency, a DSBSC signal would just look like a fading carrier. The transmit frequency stability and the reference flywheel precision would have to be very high to determione that the carrier polarity had reversed. At some point this becomes irrelevant, because the transmission path varies in length, there is drift and phase noise in TX and RX, and the signal is not received well enough to know for sure that the carrier polarity flipped. (Uncertainty again.) And although with DSBSC we keep getting pulses of carrier, they keep reversing, and on average they balance out to zero. We accept that the carrier is suppressed, we don't hear a heterodyne where we would usually hear one, etc, yet we see the carrier dancing on the oscilloscope. But over the appropriate integration time, its frequent polarity reversals cause it to balance out to zero. For most real signals, a very long time base is inappropriate. In some cases though, such as slow synchronous CW, a long time base is appropriate. So the receiver time scale should be appropriate to the signal being sought. So it's a reality check issue. Surely a carrier was not transmitted for all time, just because it existed for less than a second at some point. But just as surely, the instant of 100% negative modulation should not be reproduced as a glitch. The application of the appropriate time scale is the key, and it is up to the listener to determine what happened. Bacon, WA3WDR
Re: [AMRadio] Physical Reality of Sidebands
At 02:25 PM 1/16/2005, you wrote: there is no correct yes or no answer to the age-old question whether or not sidebands are physical reality, or exist only in the mathematics of modulation theory. It all depends on how you physically observe the signal. Sidebands physically exist only if you use an instrument selective enough to observe them. The only pure frequency is the sine wave. ANY amplitude distortion is the result of OTHER sine waves in the composite signal. I think the question above arises from the way AM theory has been taught. The simple, no math version which has been taught to technicians primarily takes into consideration the envelope as a single entity and is easier for the majority of people to understand. 73, Mark N5RFX
Re: [AMRadio] Physical Reality of Sidebands
Indeed, 'tis a puzzlement. I can draw three continuous sine waves of apppropriate amplitude, frequency and phase, corresponding to carrier, upper sideband and lower sideband, and I can add them point by point, and I can duplicate a 100% modulated AM signal waveform as we understand it. I have to believe that this works backwards; if I make this waveform by modulating a carrier in an AM transmitter, then I am synthesizing the same continuous sine waves. It seems to me that an on-off sequence would only differ from the sine wave modulated condition in the complexity of the sideband spectrum. But in the real world, sometimes theory does not produce results. For example, if there was some FM audio subchannel modulating the on-off carrier, I would simply not be able to receive it while the transmitter was off, even if I was positive that the carrier was theoretically still present. So as Dennis asked on the amradio mailing list - if a tree falls in the forest, and nobody sees it or hears it... did it really fall? When I am receiving zero, I can only know that I am receiving zero. And if there is interference, I may not even be sure I am receiving zero! And as Don pointed out, there is the question of reality, and the appearance of reality. If I took the time scale to infinity, then if a carrier was EVER transmitted, even for only a second, I would have to say that it existed for all of time. That's ridiculous! I only think that because I am integrating over all time, and then generalizing. I guess it's off when it's off, and it's signalling us when it's on. So the question becomes, at what time scale do we stop seeing beat notes, and start seeing variations and on-off switching? Bacon, WA3WDR
[AMRadio] Help with Audio driver
To All, Thanks so much for all your comets on the conversion of the BC-1 F audio driver to solid state. I really appreciated your comments, and learned a lot. I think the best is to leave it as it is as long as I got tubes and driver transformer. Don,K4KYV's comments and theory really was great, it was exactly what I wanted to know. My I wish I had the knowledge he has, now I know who to go to with questions. Don Moore W5FFK
RE: [AMRadio] Physical Reality of Sidebands
Don, I have often pondered the same thing here is another example. The Horizontal sweep rate of a TV is 15750 hz. Every 1/15000 of a sec there is a sync pedestal, and on the back porch of it is a burst of a few cycles (as I remember it was 8 to 10 cycles in length) of the color sub carrier (3.579545 MHz). This burst is removed and processed by an amplifier that is key on by the horizontal retrace pulse which has been synced to the horizontal sync pulse that rides atop the sync pedestal just in front of the color burst. The 8 cycle color burst is phase compared to a crystal oscillator in a phase locked loop. A good synchronized scope can look at the full video detected signal and spread the back porch of the sync pedestal out and view the 8-10 cycles of the burst. I often wondered what a spectrum analyzer would look like when monitoring the output of the burst amplifier with the phase detector diodes remove. The burst amplifier was a simple tetrode whose plate circuit had a parallel tank tuned to 3.58 MHZ and where the detected video was applied to the grid through a small coupling capacitor that would differentiate and pass the frequencies higher than 3 MHz. The grid leak was returned to a circuit where a positive pulse from the fly back was present to trigger the tube on. The output tank was link coupled to the phase detector. John, WA5BXO
