Jeff,
Joe is right about the distortion issues. Your "saving grace" is that you have a total passive network with just the node as a "single active source". This allows you quite a bit of leeway.
Since most distortions (CTB and CSO respectively) are caused by active devices, they are directly related to channel loading, output level and hybrid performance.
This is a major concern when running cascaded amplifiers since, CTB for example, will degrade 2dB for every 1dB of level increase. When you double your cascade, it will degrade by 6dB as a "rule of thumb". That is why we used to "degrade two line extenders in cascade" by 3dB each to equal the CTB of a single line extender in cascade in the "old days".
With your situation, you will have to work the numbers (actual channel loading) and determine if the optical transmitter in the headend has "maximum" or 100% drive power level to it.
EXAMPLE: If your transmitter has a 80 channel (NTSC) input rating for recommended input of +13dBmV and you are using only 40 channels, you could increase the input to +16dBmV to maintain 100% power and improve carrier-to-noise by 3dB. This would also increase your RX output at the node by 3dB. The "zero-dBmV" at the optical RX input is a "sweet spot" for optimum performance and light above or below would reflect the difference from manufacturer distortion calculations.
Another "rule of thumb" is for every one dB of light, you should see a 2dB change in RF.
With exceeding +50dBmV, you should confirm that the diplex filter can reject carries beyond a needed output level or it might "bleed over" as you stated.
Good luck!
Greg Tobin
Interactive Broadband Technical Services, LLC
Re: Maximum Node Output Limit?
Member #: 7190
Registered: 1996-2001
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Name:
Greg Tobin
Name:
Greg Tobin
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Interactive Broadband Technical Services
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