[AMRadio] Physical Reality of Sidebands


lwill at voicenet.com lwill at voicenet.com
Mon Jan 17 15:39:31 EST 2005


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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