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jamsys
Joined: 29 Jun 2006
Posts: 152
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| Posted: Thu Jul 03, 2008 2:30 am Post subject: How much bandwidth do you need... |
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Looking at different analog line drivers (dont need gamma and all the other stuff)
I see them rated @ 300-450mhz, but I see things like the BOX1021 rated at 1Ghz.. What is needed for 1080p
Thx
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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jamsys
Joined: 29 Jun 2006
Posts: 152
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| Posted: Thu Jul 03, 2008 2:34 am Post subject: |
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| Nashou66 wrote: | The more the merrier !!!! Get the box 1021 From what i hear its awesome.
Athanasios |
I know the BOX is great.. Just dont need gamma, and also want a line driver that has BNC connectors on it (extron)
Just need to know the bandwidth
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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jamsys
Joined: 29 Jun 2006
Posts: 152
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| Posted: Thu Jul 03, 2008 4:12 am Post subject: |
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I did read it.... WAY over my head... Tried to catch some points tho...
Wish there was a rule for 720p need x, 1080i needs x etc..
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jamsys
Joined: 29 Jun 2006
Posts: 152
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Kwint Sommer
Joined: 04 Jun 2008
Posts: 31
Location: MIT
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| Posted: Thu Jul 03, 2008 5:06 am Post subject: |
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| jamsys wrote: |
I did read it.... WAY over my head... Tried to catch some points tho...
Wish there was a rule for 720p need x, 1080i needs x etc.. |
Here's a formula you can use:
BW = [(TP x Vt) /2] x 3
Where BW = Bandwidth in Megahertz (MHz)
TP = total pixels (horizontal x vertical)
Vt = picture refresh rate in Hertz (Hz)
For example:
1080P
1920x1080 = 2,073,600 pixels x 60 Hz = 124,416,000. Divide by 2 (62,208,000), then multiply by 3 (for a 3dB bandwidth specification) = 186,624,000, or 186.6 MHz.
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jamsys
Joined: 29 Jun 2006
Posts: 152
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| Posted: Thu Jul 03, 2008 5:29 am Post subject: |
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| Kwint Sommer wrote: | | jamsys wrote: |
I did read it.... WAY over my head... Tried to catch some points tho...
Wish there was a rule for 720p need x, 1080i needs x etc.. |
Here's a formula you can use:
BW = [(TP x Vt) /2] x 3
Where BW = Bandwidth in Megahertz (MHz)
TP = total pixels (horizontal x vertical)
Vt = picture refresh rate in Hertz (Hz)
For example:
1080P
1920x1080 = 2,073,600 pixels x 60 Hz = 124,416,000. Divide by 2 (62,208,000), then multiply by 3 (for a 3dB bandwidth specification) = 186,624,000, or 186.6 MHz. |
THANK YOU!!!!!
Why the hell do people say you need 1GHZ??? (like BOX1021)
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Kwint Sommer
Joined: 04 Jun 2008
Posts: 31
Location: MIT
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| Posted: Thu Jul 03, 2008 5:56 am Post subject: |
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| jamsys wrote: | | Kwint Sommer wrote: |
Here's a formula you can use:
BW = [(TP x Vt) /2] x 3
Where BW = Bandwidth in Megahertz (MHz)
TP = total pixels (horizontal x vertical)
Vt = picture refresh rate in Hertz (Hz)
For example:
1080P
1920x1080 = 2,073,600 pixels x 60 Hz = 124,416,000. Divide by 2 (62,208,000), then multiply by 3 (for a 3dB bandwidth specification) = 186,624,000, or 186.6 MHz. |
THANK YOU!!!!!
Why the hell do people say you need 1GHZ??? (like BOX1021) |
You don't need it. In fact, 720P/1080i use about 37 MHz without the 3dB bandwidth. But, as that paper does a very rigorous job explaining, the more bandwidth the better. Even though both are above the minimum, a projector displaying 1080i with 50MHz of bandwidth will not look quite as good as one with 100MHz, all things being equal. But, in my mind a GHz is serious overkill for 1080P and I can't even recall a projector that has 1GHz of bandwidth and you're overall bandwidth is equal to the bandwidth of the weakest link in the chain.
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1031
Joined: 22 Mar 2006
Posts: 657
Location: Finland
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David_Web
Joined: 02 May 2007
Posts: 418
Location: Sweden
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| Posted: Thu Jul 03, 2008 10:58 am Post subject: |
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A line driver with a lot of bandwidth usually has some more oompf when it comes to driving the cables.
Basically the transition between a black and white pixel will be sharper and less smeared.
A 3db step is reduction of half the power so it's not something unnoticeable.
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SNR of people are ridiculously low.
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WTS
Joined: 08 Mar 2006
Posts: 1276
Location: Calgary
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| Posted: Thu Jul 03, 2008 1:06 pm Post subject: |
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Granted, the more the BW the better, but just because it has more BW doesn't mean it is a better performer than one with less BW. There are more factors involved in getting good PQ than BW alone.
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Thanks
Walter
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garyfritz
Joined: 08 Apr 2006
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Location: Fort Collins, CO
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jamsys
Joined: 29 Jun 2006
Posts: 152
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| Posted: Thu Jul 03, 2008 1:24 pm Post subject: |
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See, I always liked calculators better 
So I did 1080x1920 @ 67h and it told me 208.4Mhz bandwidth... I prob have a 60foot cable run.. So I am guessing the 300Mhz bandwidth of the extron s/b enuf?
Thx guys this is really informative!
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Thu Jul 03, 2008 2:23 pm Post subject: Re: How much bandwidth do you need... |
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| jamsys wrote: | Looking at different analog line drivers (dont need gamma and all the other stuff)
I see them rated @ 300-450mhz, but I see things like the BOX1021 rated at 1Ghz.. What is needed for 1080p
Thx |
300-450mhz is very good for line drivers, considering that's all you'll really need anyway. 1080P can be a bit of a challenge, but still those numbers are good. The bandwidth for switchers when doing 1080P should be around the 450 number.
I'm not familiar with the BOX1021 so I can't comment on how it's able to claim 1Ghz. I know of chips that are rated at that bandwidth, but those figures are only relevant for RF signals. For video (especially 75 ohm loads) you'll have to look at the devices specs. And when you do that there's so many other things that determine how well that same chip will work in that video circuit. For instance, a chips bandwidth rating has a lot to do with the output load and gain factors. So a chip could have a bandwidth of say 800mhz, but that rating is only possible based on the gain that the chip is being used in the circuit for. And in most cases especially with line drivers, the gain rating is +2. A +2 gain rating would rarely get the best and rated bandwidth of the chip.
On the other hand, too much bandwidth can be as bad as too little bandwidth. If the bandwidth rating by far exceeds the usable bandwidth ratings of the circuit, the results could be a higher signal to noise ratio, because higher bandwidth chips will amplify and produce a lot of un-wanted noise. The challenge is to achieve both bandwidth and low noise at the same time. And when doing that, you'll usually end up with a deice that's no more than three times the usable bandwidth or a bit higher.
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VideoGrabber
Joined: 09 Apr 2006
Posts: 933
Location: Michigan
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| Posted: Mon Jul 07, 2008 8:21 pm Post subject: |
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Mike wrote:
> the results could be a higher signal to noise ratio, because higher bandwidth chips will amplify and produce a lot of un-wanted noise. <
Just picking nits, but that would be a lower S/N ratio (because the noise floor is raised). [Higher S/N is good.] Everything else Mike wrote is spot-on.
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