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发表于 2013-10-18 10:49:56
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cable modem主要看三个参数,
Downstream (Rx) Receive Power Level:
This is the amount of signal received by the modem from the transmitter in the cable company head-end.
-7 dBmV to +7 dBmV "Recommended"
-8 dBmV to -10 dBmV / +8 dBmV to +10 dBmV - "Acceptable"
-11 dBmV to -15 dBmV / +11 dBmV to +15 dBmV - "Maximum"
Lower than -15 dBmV & Higher than +15 dBmV - "Out Of Spec."
Upstream (Tx) Transmit Power (a.k.a. Return Signal) level:
This is the amount of signal transmitted by the modem to reach the receiver in the cable company head-end.
+8 dBmV to +58 dBmV maximum for QPSK. (DOCSIS 1.0, 1.1)
+8 dBmV to +55 dBmV maximum for 8 QAM and 16 QAM. (DOCSIS 1.0, 1.1)
+8 dBmV to +54 dBmV maximum for 32 QAM and 64 QAM. (A-TDMA DOCSIS 2.0)
+8 dBmV to +53 dBmV maximum for S-CDMA DOCSIS 2.0 (All Modulation)
+8 dBmV to +52 dBmV maximum for A-TDMA & TDMA (DOCSIS 3.0)
SNR (signal to noise ratio) levels:
This is how clear the signal is at either the modem receiver (downstream SNR) or the receiver in the cable company head-end (upstream SNR).
QPSK: 12 dB minimum. 15 dB or higher recommended. (often used in upstream channels)
16 QAM: 18 dB minimum. 21 dB or higher recommended. (often used in upstream channels)
64 QAM: 24 dB minimum. 27 dB or higher recommended. (often used in downstream channels)
256 QAM: 30 dB minimum. 33 dB or higher recommended. (often used in downstream channels)
信号强度是以dBmv为单位,如果Comcast那人说的是downstream level 36dBmv,你加一个splitter大概衰减3.5dB,应该没有帮助,这个level一般都不会太高,就算真的过高,也应该在户外Comcast线路放大器来调。如果他真说dB,那应该是指信噪比SNR,它应该越大越好。最简单方法,下次你安装自己买的那个cable modem时,试试不用这个splitter,看看有能不能正常工作就知道。
你图中这个网速不是连接Internet的速度,它显示的是你电脑网卡的连接router的速度,你Internet的速度可以点击这个链接测试Comcast Speed Test
by:玫瑰玫瑰花园967叶西关小姐 |
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