Church and H.O.W. – Forums for HOW Sound and AV - Your Displayed Name Must Be Your Real Full Name To Post In The Church and HOW Forums > H.O.W. AV Archive

Composite video ghosting, 50 ft run will an amplifier cure it?

(1/3) > >>

Jerrybosun:
I have  4 RCA lines run that I am taking a composite video signal from an HD cable box (1 dig audio & 3 video RBG)  and running it to a large screen LCD. I am getting some ghosting on what appears to be more than one color with different ghost horizontal smearing. I used high quality wire and soldered my own connections, (I am a great solderer... forgive my little sin of pride) and there is no big RF/Power lines crossing the path.  The Digital audio is working fine.

Unfortunately these have been buried and drywalled over already. Sooo.... I have a few questions.

1. Will this amp/distributor help the ghosting.
2. Is there a cheaper solution.
3. Is this too cheap of a solution? (do I need a higher end 3 channel (RBG) video amp
4. Does HD make a difference on the type of amp I buy?

FYI ebay sale #120275840797   .. Title is    "3 in 9 Out Composite Video Splitter Distribution Amp"

Brad Weber:
What did you use for cable?  This is video, not audio, so it should be coax video cable and not audio cable.  And 50' is getting a bit long of a run for the tiny coax cables normally used with RCA connectors, with the longer run and cable buried in walls I probably would have used RCA-to-BNC adapters and full size coax.  That being said, I know people that have run video on audio cable for longer distances, however that was for composite video applications rather than component video.

This could be a tricky one to figure out as you are dealing with several potential issues such as the quality of the cable signal, how good an analog output the cable box provides, how the LCD display processes the component analog input and so on along with the cable itself and the result could reflect multiple of these factors.  If you could temporarily get the cable box closer to the LCD display and use a short, component video cable for the connection then that might let you verify if the problem is really, or at least primarily, the cabling.

Many distribution amps only provide gain to make up for the multiple output split, they do not necessarily provide any additional gain.  According to the eBay listing that particular one supposedly does provide additional gain but it is not clear how much.

Jerrybosun:
Yes I did use high quality copper shielded audio wire.
I tried  moving  the box closer and it works 100% with a 6 foot run,  
Yeah this unit is a true amp not just a splitter.  480Mhz but no db info..

Brian Ehlers:
For transmission of high-speed signals -- and yes, composite and component video are high-speed signals -- it is extremely important that the entire path be impedance matched.  The driving amplifier must be of high-quality and drive the signal with a particular impedance (typically 50 or 75 Ohms).  The receiving device must provide termination matched to this impedance.  And every inch of cable and every connector in between the driver and receiver must also be matched to that impedance.

Wait, I can hear everyone scream now, "But I've been using the cheap video cables forever and never had a problem."  Good for you.  But the more you push the envelope, the better chance you'll experience unacceptable degradation.

Sending video through "audio wire" (whatever that is) for 50 feet, and using RCA connectors (which are inherently not suited for video, despite being "standard") is indeed pushing the envelope.  What happens is that when the signal hits an impedance discontinuity, part of that signal reflects back the other direction.  When it hits another discontinuity, it reflects back again.  Do this over a long enough distance with analog video, and a ghost image is exactly what I would expect to see.  Do it over a very short distance (say, from your home VCR to TV) and you only get a slight smearing that no one notices.

It is possible that the distribution amplifier you are considering will do a better job of driving your wiring, but it's more likely you need to optimize the wiring instead.  Or use a different transmission method.

Jerrybosun:
Thanks Brian,
Your explanation made a ton of sense. It cleared up a few misconceptions that I have had since the 1980's.  So this amp may actually work but it will be doing so by overwhelming the reflections that are causing the ghosting smear.
1. Would a filter and or impedance matcher help in any way?
2. If so, what type?
3. If so, where would you located it in the signal path?

Navigation

[0] Message Index

[#] Next page