Originally Posted by
redburgundy
An amplifier *might* help a cable modem. The downstream signal (cable headend to home) is usually carried in the same frequency range as the video, 54 MHz up to 600 to 800 MHz, and usually near the upper edge; the frequency of the upper edge depends on the specific cable system. If the downstream cable modem signal is right at the upper edge, and if the cable signal strength "rolls off" at the high frequency end (decreased amplitude), then an amplifier could help the cable modem signal. The upstream signal (home to cable headend) is carried in the frequency range below 50 MHz, and indeed amplifiers cannot help the upstream signals.
Amplifiers tend to cause more problems than they solve. Almost all are passive return and have an insertion loss penalty that can cause far more problems than the downstream amplification potentially solves.
Active return amplifiers exist, but require much more careful setup to avoid causing massive problems for everyone on the node. Whereas a downstream amp only screws you up if it's not set up correctly, an upstream amp that's misconfigured will result in a visit from the cable co in fairly short order. I've heard of an 'automated' active return amp that is self-controlling but haven't seen one yet.