[AMRadio] Physical Reality of Sidebands


lwill at voicenet.com lwill at voicenet.com
Wed Jan 19 08:48:09 EST 2005


Hi John,

Yep I agree on all this.  Actually I and Q as I remember was a Hazelteen (sp) 
patent that RCA had to buy.  the R-Y B-Y detector was developed by RCA later to 
avoid the license fees from Hazelteen.

Growing up into color TV near RCA's plants and Sarnoff was ben a bif help to me on 
early undestanding (college years0 of how color worked.

I actually worked with RCA Sarnoff while DE at NJ Network on their first HDTV analog 
system which used yet another subcarrier in the imaginary plane at about 3 mhz to 
add the side panels for the wide screen.

Amazing math tricks are used in all this.

Kepp up the good work.

Larry


On Mon, 17 Jan 2005 21:12:42 -0600, "John Coleman, ARS WA5BXO" 
<wa5bxo at pctechref.com> wrote :

> 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: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of lwill at voicenet.com
> 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" 
> <wa5bxo at pctechref.com> 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
> > 
> > 
> > 
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