CATV Archives - Everybody Staze...

Since moving into my home, I’ve had my cable modem in our office. A room above our garage that has coax run to it from the garage, which is where the CATV coax enters the house. Coax enters the house through a wall, goes into a splitter, and heads from there up to our office. Total run length from the splitter is about 30ft. With the modem in the office, and then in the garage, the data for the modem follows (Update 5/26/11: After a couple days, the signal levels changed a bit in its new location. I’ve found online that 6 dBmV is actually a bit on the high side for signal strength, but within acceptable limits):

	Office	Garage	Garage 2
Downstream Freq	567.00 mhz	567.00 mhz	579.00 mhz
Downstream Power	3 dBmV	4 dBmV	6 dBmV
Downstream SNR	36 dB	36 dB	35 dB
Modulation	QAM256	QAM256	QAM256
Upstream Freq	32.400 mhz	32.400 mhz	22.800
Upstream Power	44 dBmV	43 dBmV	42 dBmV
Channel Type	DOCSIS 2.0 (ATDMA)	DOCSIS 2.0 (ATDMA)	DOCSIS 2.0 (ATDMA)
Symbol Rate	5120 kSym/sec	5120 kSym/sec	5120 kSym/sec
Modulation	QAM64	QAM64	QAM64

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Ungrounded CATV coax connections can cause some rather bad speaker hum (at 60hz here in the US), and horizontal lines in your picture. Grounding your coax connection can help alleviate these problems, though it may not fully solve your issues. To demonstrate, here’s some backstory.

We have a older CRT TV in the garage that we use to play DDR/Stepmania, as well as have a TV going when working in the garage. I recently hooked an old computer up to the TV for a permanent Stepmania machine. Right after hooking this computer up, I started getting a really bad ground hum on the TV, which could be quickly fixed by installing a ground lift (Cheater Plug) on the computer power connection, but this is generally a bad idea (computers like being grounded). After doing some research, I found out that an ungrounded CATV connection can cause ground hum. Checking it out, I removed the CATV connection from the TV, and viola, the hum was gone. Okay… so, now to actually FIX the problem.

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Moving the modem

Ground your cable TV coax!