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
