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bchandler02

join:2011-07-08
Oklahoma City, OK
reply to xymox1

Re: High freq attentuator

what are your current signal levels?



xymox1
Premium
join:2008-05-20
Phoenix, AZ

+7 and yea they are within range, but I have some technical reasons I want to hit 0.

My up stream are 39.5 and I dont want to increase my output power.

I want a mfgr of a low pass attentuator with low insertion loss below 54mhz and 6db up at 850Mhz.



bbeesley
VIP
join:2003-08-07
Richardson, TX
kudos:5

said by xymox1:

My up stream are 39.5 and I dont want to increase my output power.

Actually, you do want to increase your output. The higher you can get it without going over ~52db the better your signal to noise ratio will be

as long as you aren't exceeding the DOCSIS 55db spec and/or clipping the output, higher is better


odog
Cable Centric Vendor Biased
Premium,VIP
join:2001-08-05
Atlanta, GA
kudos:14
Reviews:
·Comcast
reply to xymox1

said by xymox1:

+7 and yea they are within range, but I have some technical reasons I want to hit 0.

My up stream are 39.5 and I dont want to increase my output power.

I want a mfgr of a low pass attentuator with low insertion loss below 54mhz and 6db up at 850Mhz.

Your technical reasons are what? FYI that type of filter is generally not made. They also don't normally knock the signal down just a few dB. Most low pass filters have 30-40dB rejection in the stopband, sometimes more. About the only way to get what you want is to dilpex the signal, then pad the "high" side. That 0dB input probably isn't worth the return penalties of adding another diplex.
                   HIGH 6dB pad----"out" two-way
signal---diplex                                             "in" two-way-- CM
                   LOW------------"out" two-way
 

said by bbeesley:

Actually, you do want to increase your output. The higher you can get it without going over ~52db the better your signal to noise ratio will be

as long as you aren't exceeding the DOCSIS 55db spec and/or clipping the output, higher is better

Higher is not better, and not really higher. Ultimately the signal is still at 0dBmV at the upstream receiver in the CMTS, and same levels as other modems in most of the plant before it gets there.

For example, you have a modem on the "through" leg of a 12dB direction coupler.(aka uneven splitter) A DC12 has three ports, an input, a 12dB down tap leg, and through leg with loss of 1dB. For demonstrative purposes a modem hooked directly to the input cable has a TX power of 30dB. Hooking your modem up on the through leg of the tap gives you a return power of ~31dB. I hook my modem up to the DC12 tap leg and my modems power is ~42dB. If you look at our modems power levels, they are ONLY different until we get to the DC12. After that we have identical power on the wire. If it happened any other way this whole DOCSIS thing wouldn't work.


bbeesley
VIP
join:2003-08-07
Richardson, TX
kudos:5

said by odog:

If you look at our modems power levels, they are ONLY different until we get to the DC12. After that we have identical power on the wire.

True, but I want to exit my house as high above the noise floor as possible without clipping as this is where the majority of return path impairments would be potentially generated on the plant