CCTV video quality suffers when connected alongside Cable TV

[ehzzy 0]

We recently tried to set up some CCTV cameras for our home and everything is fine except that the CCTV video feeds from some of the cameras suffer when we try to simultaneously connect the DVR and cable TV to a Samsung LCD TV monitor. It work's fine if you only connect them one at a time, but the moment you try them both (since we want a TV that's also a CCTV monitor) things just go bad. They're both on separate inputs though, with the DVR on the TV's VGA port and the cable TV connected through (what I think is) a UHF connector so I really don't see a reason for why this should be happening.

 

There's also only one other monitor which is connected only to the DVR through a different DVR output labelled 'Main Out" which uses a BNC connector to connect the DVR to the monitor (the other monitor with problems uses the VGA out). This one is also affected by the drop in quality when we try to connect the cable TV to the other monitor.

 

We've tried several things to try and fix this: We've tested this with different TVs (different brands and types), we've tried completely disconnecting the other monitor attached to the DVR, and we've tried switching out the power supply for the 5 cameras that are affected. All of it doesn't seem to make a difference.

 

Any help or advice would be appreciated. Thank you.

[Soundy 1]

Sounds like a ground-loop issue somewhere, but narrowing it down could be tricky with so many variables. You could try isolating the power grounds on each device using a ground-lift plug:

 

[ehzzy 0]

Will do and thanks for the quick reply. Wikipedia says something about these plugs being dangerous though so I'm assuming that these are just for testing and not a permanent solution.

 

Just some additional information:

The cameras are divided in two sets, each with their own power supplies. One set of 5 with a 20 ampere power supply and another set of 3 connected to a 6 ampere power supply. It's only the 5 with the 20 ampere power supply that go wrong when the cable TV is connected. Both sets are physically located pretty far away from each other.

[Soundy 1]

Will do and thanks for the quick reply. Wikipedia says something about these plugs being dangerous though so I'm assuming that these are just for testing and not a permanent solution.

Keep in mind that ANYONE can write or edit a Wikipedia article, so take that accuracy for what it's worth... these CAN be dangerous if used improperly, in certain situations where a ground is REQUIRED for safety. In this case, it's not. We used to use them regularly in the studio for lifting grounds on guitar amps when they caused interference issues... and sometimes actually to IMPROVE safety (ever seen a spark jump from a mic to a musician's lip because a leaky circuit is trying to find a ground through him via his amp's ground?)

 

You can alternately snip the ground plug off your various equipment's power cords, but that's kind of a more permanent thing... these will allow you to test the theory first.

 

Just some additional information:

The cameras are divided in two sets, each with their own power supplies. One set of 5 with a 20 ampere power supply and another set of 3 connected to a 6 ampere power supply. It's only the 5 with the 20 ampere power supply that go wrong when the cable TV is connected. Both sets are physically located pretty far away from each other.

That would make sense - when using a common power supply for multiple cameras, it means all those cameras are sharing a ground. They're also sharing a ground at the DVR, through the video connections.

 

The DVR is then grounded via its own power cord. The TV's power cord may also be grounded. If not, the TV is still grounded via the VGA connected to the DVR. The TV is then ALSO grounded via the cable input. At a guess: does the 20A power power supply have a grounded plug, and the 6A supply just a two-pronged plug?

 

With all those different ground paths, it's pretty easy to get some differential levels happening, and thus have noise introduced.

 

I didn't notice if you'd said already, but is everything okay if you disconnect the RF cable from the TV? It's not uncommon for the incoming cable feeds to have poor grounds that can cause various issues - that final connection between the CCTV and TV systems could easily be enough for the two to generate noise.

[bpzle 0]

what is a "uhf connector"? do you mean "f" connector for cable tv?

[ehzzy 0]

what is a "uhf connector"? do you mean "f" connector for cable tv?

It's actually the RF cable, my mistake. I'm not very familiar with these things.

 

At a guess: does the 20A power power supply have a grounded plug, and the 6A supply just a two-pronged plug?

I'm away right now so I'll have to look at that when I get back there. From what I recall both power supplies were two-pronged but I'll have to double check on that.

 

I didn't notice if you'd said already, but is everything okay if you disconnect the RF cable from the TV? It's not uncommon for the incoming cable feeds to have poor grounds that can cause various issues - that final connection between the CCTV and TV systems could easily be enough for the two to generate noise.

Yes, everything works perfectly when we disconnect the RF cable (for the cable TV?) from the TV.