Hi,
Now that the weather is becoming warmer with each day, I have noticed that the downstream power level to my cable modem is beginning to decrease. The warm weather also is causing my cable modem to increase it's upstream power level as well. The SNR is also slightly decreasing with warmer weather. During the very cold nights last winter, I was seeing SNR at around 38 and. With the warm days now (currenty 80 degrees), the SNR is between 35 and 36. Downstream power has gone from -3.5 and -4 dBmV to between -7 and -8 dBmV. Upstream power has gone from 42 dBmV to 45 dBmV. Everything still looks well within specs, but I'm concerned that it may pass the thresholds once the 90+ degree temperature arrives.
The cable modem is located right where the cable comes into the house, connected to a wireless router. There are three pieces of additional hardware giving attenuation to the cable line once it comes in: a surge protector, a splitter, and a male/male coupler. The splitter is very solid, it's frequence range is rated up to 1Ghz, and it is spec'd at giving 3.5 dB of attenuation. As a recent test (while 80 degrees outside), I ran the cable line coming in directly to the modem to see what the downstream was and it was a solid +1 dBmV. I then ran it through the splitter (plus a three foot section of my own RG6) and got -2.5 dBmV. I then added the coupler to the splitter, and found it to give an additional 2 dB of attenuation. So, with the splitter, coupler, and a small section of my own RG6, the downstream power level is at -4.5 dBmV -- attenuating the original
+1 dBmV by 5.5 dB.I then ran it through the surge protector, which seems to introduce another
2.5 dB of attenuation. The attenuation of the surge protector, however, doesn't seem constant. It seems to jump between 2 and 2.5 dB -- giving the total output between -7 and -8 dBmV.Unfortunetly, I never took at look at signal level coming in during the cold weather. I suspect that it must have been hotter than +1 dBmV though, since I was using the surge protector, splitter, and coupler at the time and seeing between -3.5 and -4 dBmV.
This will be the first summer that I will have the cable modem. Should I expect much more loss as the weather begins to climb from 80 to 90+ degrees? As I have read, the range for the downstream power level should be between -15 and +15 dBmV, but idealy you want to keep it within -10 and +10 dBmV -- with 0 dBmV being optimum. Should I look at removing one of the three pieces of hardware before the summer months arrive? Perhaps locating a good splitter that has a female connector for input and males for the two outputs (to remove the coupler)? Is the surge protector absolutetly necessary for coax -- or does the cable modem (plus the cable HDTV STB box) provide their own surge protection for the coax inputs? All the electrical inputs for the cable modem, router, HDTV, STB, Dolby Digital receiver, ect are all going through the surge protector of course.
Or, perhaps, I really don't need to be too concerned about it. From everything that I have, it all looks well "in the green".
Is this looking pretty good?
Currently, at 76 degrees outside, and cable uses QAM 256:
Downstream power level: -6 dBmV SNR: 36 dB
Upstream power level: 45 dBmV (This will fall back to around 42 dBmV by evening. Without the splitter, coupler, surge protector, it only requires around 38 dBmV to talk to the cable company.)
Thanks!
-ES