deeptho
Specialist Contributor
- Joined
- Apr 7, 2006
- Messages
- 701
- Reaction score
- 422
- Points
- 63
- Age
- 57
- My Satellite Setup
- Wavefrontier T90, Laminas 120cm, 2 other dishes; tbs 5927, tbs6904, tbs6909x, tbs6903x, tbs5990, tbs6981,tbs5927
- My Location
- Europe
The last couple of days, we started loosing TV reception on cable TV: from time to time
heavy pixellation occurred on many channels on two muxes. This lasted for several minutes
and then the problem disappeared for a while.
I finally found out that the problem was due to interference from a 3 meter long HDMI cable
in a room in a completely different part of the house. The Aha-momemnt came when I discovered that
the problem went away when the computer activated the screen saver. Apparently sometimes
the screen woke up because the mouse reacted to small vibrations, but because the monitor is
mostly off and the computer mostly on, I did not notice.
I then replaced the HDMI cable by another one, and the interference became even stronger.
All TV pictures went away fully. The PC is not even connected to the cable system but a cable coax comes
close to the hdmi cable at some point.
I noticed the strongest interference on 147MHz, 294 MHz (the former only when the PCs screen is ot
blanked) and 300 MHz (constant even if screen is blanked). The 294MHz caused the picture problems.
Interestingly I can change the center frequencies of the interference by changing
the PC's screen resolution and I can spread it around by playing a video.
So here is the question: are these HDMI cables really that badly shielded? The first one was a regular round cable and
was installed many years ago. I never noticed problems. There could have been interference already but perhaps
not yet strong enough to notice.
I did disconnect the pc recently and reinstalled it in the same place. So perhaps some minor damage to the connector
could cause problems like this?
The second cable is a flat ribbon cable (and brand new).
heavy pixellation occurred on many channels on two muxes. This lasted for several minutes
and then the problem disappeared for a while.
I finally found out that the problem was due to interference from a 3 meter long HDMI cable
in a room in a completely different part of the house. The Aha-momemnt came when I discovered that
the problem went away when the computer activated the screen saver. Apparently sometimes
the screen woke up because the mouse reacted to small vibrations, but because the monitor is
mostly off and the computer mostly on, I did not notice.
I then replaced the HDMI cable by another one, and the interference became even stronger.
All TV pictures went away fully. The PC is not even connected to the cable system but a cable coax comes
close to the hdmi cable at some point.
I noticed the strongest interference on 147MHz, 294 MHz (the former only when the PCs screen is ot
blanked) and 300 MHz (constant even if screen is blanked). The 294MHz caused the picture problems.
Interestingly I can change the center frequencies of the interference by changing
the PC's screen resolution and I can spread it around by playing a video.
So here is the question: are these HDMI cables really that badly shielded? The first one was a regular round cable and
was installed many years ago. I never noticed problems. There could have been interference already but perhaps
not yet strong enough to notice.
I did disconnect the pc recently and reinstalled it in the same place. So perhaps some minor damage to the connector
could cause problems like this?
The second cable is a flat ribbon cable (and brand new).