Talk:8VSB

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Comments[edit]

There is a link to a spectrum analizer product, which looks like an advertisement. And the sections on instruments cite it too. Moreover, the final section on digital radio standards has nothing to do with 8VSB. Cantalamessa 09:59, 27 January 2006 (UTC)[reply]

Bifurcation of digital transmission systems[edit]

This is an interesting topic, but shouldn't it be moved to a more relevant article? Serrano24 16:10, 13 November 2007 (UTC)[reply]

Agreed. Actually the HD Radio article already covers this. As it has nothing to do with either 8VSB or ATSC, I've purged the section --208.152.231.254 (talk) 18:24, 28 October 2009 (UTC)[reply]

Power levels not lower[edit]

The section that claims ATSC transmitters operate at lower power is comparing apples to oranges. NTSC power is measured as peak power. Typically, this is the power of the sync pulses, which have a much higher amplitude than white (video is inverted before amplitude modulating the carrier). ATSC power is measured as average power, and for ATSC typically average power much closer to peak power simply because of the random nature of the modulating data. —Preceding unsigned comment added by Nsayer (talk • contribs) 17:39, 15 August 2008 (UTC)[reply]

ATSC's average power is still lower than NTSC's average power. In order to get NTSC average power, divide the peak by 1.6, and you will find it's about four times higher than ATSC values. --- 149.32.192.33 (talk) —Preceding undated comment was added at 18:32, 30 September 2008 (UTC).[reply]
Um, where do you get the 1.6 factor? Citation needed... Nsayer (talk) 22:06, 7 October 2008 (UTC)[reply]

Television Broadcasting:Equipment, Systems and operating fundamentals page 601 lists the factor as 1.68 for an all black analog signal. At 50kw average power the peak power is 84kw. A 50 kw digital transmitter sends out its peaks at 200kw. The FCC allowed analog stations a maximum of 5 megawatts ERP but only allows digital stations a maximum of 1 megawatt ERP The real measure is service area. The FCC charts show they are comparable with the lower average power. "Your mileage may vary" —Preceding unsigned comment added by Stairstep24 (talk • contribs) 21:28, 30 May 2009 (UTC)[reply]

The NTSC average power level depends on scene brightness, so it can (could) vary quite a bit. Black is maximum power (except for blanking and sync, which are even higher) and white is minimum power, so a brighter scene means lower average power. The peak power remained constant since it is set by the sync pulses, so the peak-average ratio was larger for a bright scene.

The NTSC transmitter I ran in my youth (WMPB-TV, channel 67) used klystrons that were essentially "efficiency modulated". I still remember the numbers: DC input power to the visual klystrons was constant at 18 kV * (2*4.5A) = 162 kW regardless of signal level. As I recall, the peak (tip of sync) efficiency was only about 30%, and given the non-trivial electric bills for a continuous 162 kW load, things like peak/average power ratios really matter. A lot.

Karn (talk) 09:47, 26 January 2018 (UTC)[reply]

Context in introduction[edit]

I came here trying to find out what "8VSB" meant in the specifications of a TV I was looking at, and found the "this introduction needs to provide more context" tag. I was able to understand the introduction well enough to answer my question, so I edited the introduction to answer it for those less technical than I am. If someone thinks it doesn't fit well enough with Wikipedia style, I won't object. Metageek (talk) 18:25, 10 August 2009 (UTC)[reply]

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QAM[edit]

Hello all,

The DVB-T standard uses OFDM, but is modulated using QAM16 or QAM64. The modulation method presented here mentions only QAM for cable. QAM is the method by which (C)OFDM or any other mehod is modulating a signal. Gerben49 (talk) 17:53, 29 November 2018 (UTC)[reply]

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