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
