Comcast intermittent on some HD channels

[Art_B]

I'm experiencing intermittent signal strength on a limited number of Comcast HD channels. The problem channels are all in a narrow frequency band; 747000 KHZ (724) and 753000 KHZ (707 and 709). I've seen the signal strength vary dramatically on an hour by hour or day by day basis. At mid evening tonight, 707 was showing no signal for several hours. In late evening, it jumped up to 86. 709 also showed similar symptoms. I'm located in Sunnyvale, CA.

I don't think the problem is due to poor cabling or loss of high frequency signals within my house. I've just recently replaced the entire cable run between the Comcast connection and the TV with a brand new RG 6 cable. And a station at a higher frequency point, 807000 KHZ (720), shows a consistent reading of 90.

I have two of the S style cablecards. The problem is present on both tuners / cablecards.

My guess is that the problem is due to a poor signal from Comcast. Have others seen this problem of selective intermittent loss of channels? Since the signal strength is moving hour by hour and day by day on the bad channels, this is going to be hard to demonstrate to Comcast.

[ewilts]

Been there, done that. Comcast ended up putting in an amplifier and all of my problems have been solved. I had mild to serious pixelation (depending on time of day) on only a narrow band of channels.

Comcast initially charged me for the amplifier but when I disputed the charge, they immediately gave me a credit.

[Art_B]

Thanks much for the info on your experience. An amplifier could be the solution.

I was wondering if anyone knew how to equate the TiVo signal readings to actual cable loss numbers (dB)? The TiVo numbers are usually about 90-95 on most of my channels. And 60-45, or even no signal present on the problem channels. Signal gain/loss is normally measured in dB. I believe an amplifier might have a typical gain of about 10-20 dB. I'm not sure what a TiVo signal 30-50 below the norm actually means in terms of dB of signal loss. Or how much amplifier gain is required to correct it. The TiVo numbers appear to be much too large to be measured in dB.

[fronesis]

If you tune to a channel and then go into the 'DVR diagnostics' menu, it will show you dB numbers. In my experience it's impossible to correlate the 'signal strength' with actually dB signal - on some channels I'd have 30 dB and a signal strength of 100; on others I'd have 33 dB and a signal strength of 75.

[Art_B]

I was finally able to resolve the problem with intermittent signal. The Comcast technician disconnected and reconnected their cable run at two points outside of my house. Since then, the signal has been rock solid. On all channels I've checked, the signal now measures a consistent 90-95 on the Tivo. And there have been no problems with picture drop out.

He did the disconnect/reconnect operation at my service entrance box, and at a cable pedestal across the street. My guess is that the problem was at the pedestal. All connections he checked appeared to be well tightened, including the one at the pedestal. But disconnecting and reconnecting it cleared the problem. I would guess the issue was slight oxidation of the connection.

Getting to the solution was a long, frustrating march. Over a period of weeks, and several visits, Comcast blamed the problem on my Tivo, on the cable cards, and on my house coax wiring. Replacing the cable cards in the Tivo did not resolve the problem. And required two phone calls to Comcast, plus a technician visit to get the new cable cards working. I had already replaced the wiring once, and was reluctant to replace it again.

I eventually rented a DVR from Comcast and set it up in the garage with a small TV, and connected the DVR to their inlet cable. Their DVR showed the same occasional intermittent symptoms as my Tivo in the living room. To document the intermittent nature of the problem, I took pictures of the garage TV versus the Tivo connected TV. On one evening I watched the Tivo signal strength move from 0 to 72 in three minutes. And six hours later it was back to 0. At that point they finally accepted that the problem was not inside the house.

As part of resolving the problem, I tested the Tivo and the Comcast DVR side by side, connected to the same TV in my living room. I had both units connected via a splitter, driven from a common coax feed. The Tivo had somewhat better ability to work with a weak signal than the Comcast DVR.

I will say in fairness to Comcast, the intermittent nature of the problem made this hard to trouble shoot. It wasn't until I watched the signal move from 0 to 72 in three minutes that I understood how rapidly the signal could change. And how careful I had to be to recheck the problem, after making changes and assuming I had fixed something because the signal level was now different.