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Why is a video amp also known as wideband amp? - RF Cafe Forums
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| dookkie |
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Post subject: Why is a video amp also known as wideband amp?
Posted: Sat Mar 24, 2012 12:25 pm
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Joined: Sat Mar 24, 2012 11:57 am
Posts: 1
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Just curious as to why is video and wideband used interchangably in this case. Any help
is greatly appreciated. Thanks
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| wb9jtk
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Post subject:
Posted: Tue Mar 27, 2012 3:17 pm
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| General |
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Joined: Tue Dec 26, 2006 5:39 pm
Posts: 66
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People often refer to any wideband amplifier as a "video amp" even though it might not
be amplifying video at all.
In analogue television, you needed to faithfully
reproduce from near dc to 4.25 MHz. The color signals were 3.579545 MHz +/- 0.3 Hz,
horizontal sync pulses were 15,734, vertical sync were 59.94 Hz. The synch pulses were
very 'square' with very high rise and fall times.
Signals going to the crt beam
guns had been stripped of synch pulses, just the luminance information remaining. A
high contrast image might have content up to nearly 4.5 MHz in it, but an "all white"
or "all black" (or all gray) image would require reproducing 0Hz in the beam control
circuits. The surprising thing is that B&W tube tv receivers used a.c. coupled amplifiers
but did an impressive job amplifying down to 0 Hz !
Its not impressive that
the video amps had a 6 or 8 or 10 MHz bandwidth... the impressive thing is that the
high frequency capability was 6 million times higher than the low frequency, and the
phase shift had to be well controlled through that extremely high ratio.
So for
all of my life, when people say "video amp" they might not be referring to an amplifier
amplifying video, but any very high bandwidth amplifier.
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| Syncopator
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Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Fri May 25, 2012 1:17 pm
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Joined: Fri May 25, 2012 1:05 pm
Posts: 2
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dookkie wrote:
why is video and wideband used interchangably?
Because the word video
means wideband. Or at least it did until
the uninformed media heard and typically misunderstood it. The Hewlett Packard
3400A RMS Voltmeter, a rather ancient instrument now, has a video amplifier (because
it has a bandwidth of 10MHz) and the technical manual refers to it as such.
_________________
Equal rights for equal responsibilities.
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Kirt Blattenberger |
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Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Sun May 27, 2012 11:17 am
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| Site Admin |
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Joined: Sun Aug 03, 2003 2:02 pm
Posts: 878
Location: Erie, PA |
Syncopator wrote:
Equal rights for equal responsibilities.
A profound statement whose meaning could easily be missed...
_________________ - Kirt Blattenberger
 RF Cafe Progenitor & Webmaster
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| Syncopator
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Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Sun May 27, 2012 11:29 am
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Joined: Fri May 25, 2012 1:05 pm
Posts: 2
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Yes Kirt.
This site doesn't allow enough characters to post the signature which
I use elsewhere:
Equal rights for equal responsibilities.
Equal opportunities
for equal abilities.
_________________
Equal rights for equal responsibilities.
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Posted 11/12/2012
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