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Why is a video amp also known as wideband amp? - RF Cafe Forums

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dookkie
 Post subject: Why is a video amp also known as wideband amp?
Posted: Sat Mar 24, 2012 12:25 pm 
 
Lieutenant

Joined: Sat Mar 24, 2012 11:57 am

Posts: 1

Just curious as to why is video and wideband used interchangably in this case. Any help is greatly appreciated. Thanks

 
   
 
wb9jtk
 Post subject:
Posted: Tue Mar 27, 2012 3:17 pm 
 
General
User avatar

Joined: Tue Dec 26, 2006 5:39 pm

Posts: 66

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.


 
   
 
Syncopator
 Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Fri May 25, 2012 1:17 pm 
 
Lieutenant

Joined: Fri May 25, 2012 1:05 pm

Posts: 2

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.


 
   
 
Kirt Blattenberger
 Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Sun May 27, 2012 11:17 am 
 
Site Admin
User avatar

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...

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Syncopator
 Post subject: Re: Why is a video amp also known as wideband amp?
Posted: Sun May 27, 2012 11:29 am 
 
Lieutenant

Joined: Fri May 25, 2012 1:05 pm

Posts: 2

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.


Posted  11/12/2012

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