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Author
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Topic: making video cables
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 06-30-2008 11:02 AM
As with all cable making...don't cheap out. That includes the cables, connectors and the tooling. If you are going to be making only a couple...then it will be expensive and probably best to just buy what you need premade. If you are going to be making a lot...then it is time to tool up.
Copper video cables are Coax as one is trying to emulate a transmission line such that the impedence remains constant. Low capacitence is also key in keeping the signal good over long distances.
For HDSDI...Belden 1694A is the standard by which others are judged. While I'm sure there are others out there that may be better, 1694A is the benchmark. It is an RG-6 class of cable. Connectors are available from most any of the common manufacturers. We use AMP but most Broadcast types use Kings.
Likewise, most of the crimper manufacturers will have a die set for 1694A. Again, we use AMP but many use Paladin.
SDI can travel on 1694A just fine too and as such, you will likely find it is cheaper to stock fewer spools of cable than to have one for each and every type. Note too, as you increase your cable types, so must your crimpers, crimps and dies increase. With Coax, it is ESSENTIAL to have the proper crimps and dies...don't make do with what you have...the resulting crimp will be poor and the impedence will suffer.
For SDI, I see 1694A and 1505A quite a bit.
For the analog stuff you will see everything under the sun...again 1694A is suitable and will transmit NTSC type signals about 300-feet without any need of a booster or peaking amp. However most use some form of mini-coax...those normally will cause video signals to visibly suffer in less than 100' and with computer signals within 35-feet...depending on the cable.
There is also a bit of a marking in pushing video over Cat-5 cables...watch out...you will get color timing issues if you don't use some form of skew-free cables and not all systems are created equal.
So your question is wide open...what specifics are you looking for?
Steve
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Bruce Hansen
Jedi Master Film Handler
Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999
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posted 06-30-2008 06:59 PM
1694 is good for long runs, even 1505A (RG-59 size) will go 300 feet with 1.5 Gig HD-SDI (personally I don't think I would try to push it that far). For short runs, like when wiring in racks, I would use 1855A. It is smaller than 1505A. Using anything larger on racks with lots of DAs or racks with lots of patch panels will pack your racks so full of cable, you will not be able to get to the back of the equipment. 1855A is also lighter weight. That is a BIG plus in a big production truck where there is a road weight limit. BTW, Beldon says that 1855A will go up to 210 feet with HD-SDI. Want something even smaller, Beldon makes an HD-SDI verion of RG-179.
I like the crimp on connectors. There are crimp on RCA connectors as well. One thing to be carefull of, a lot of RCA connectors in consumer equipment are held in place by the solder connection to the circuit board. Solder is soft, and the connector can easly be torn from the board if too much pressure is put on it by the connector pluged into it. For this reason, I like to use crimp on RCA connectors with 1855A type cable. Using an RCA to BNC adaptor, and RG-59 type cable is more likely to cause a problem. Of course, any video connection using an RCA connector will be analoge, so fell free to solder on that RCA connector.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 06-30-2008 10:52 PM
As for testing...the number bad crimps we encounter (that we hae made) are next to none as we use high-quality cable/crimps and crimpers (we also use good cable strippers). When we adopt a cable type, we set up a kit that has a striper calibrated for it, crimper dedicated for it and crimps specific for it. It really does go a long way towards good performance.
If our cables are shop made, then we generally will do a continuity test to ensure everything was done properly and there are no shorts. This is not an exhaustive test by any stretch and does not take into account frequency losses.
If you are looking into that sort of testing...you merely need an impulse generator and an O'scope that is fast enough to show the loses. When I'm in the field, I'm normally using some form of Multi-burst pattern and an O'scope. A multi-burst pattern will have progressively higher frequency pattern to it that will show HF rolloff in the video just like pink noise will do for your analog soundhead.
For digital video...the problems will show up as hits at first and progressively look worse as you are not getting a steady complete image. There are other factors at play too...how good is the transmission device and how good is the receiving device? I've seen some HDSDI devices that couldn't deal with a cable less than 100-feet long...in fact it topped out at about 35-feet. Put a repeater on the exact same 100-foot cable...no problems at all...the repeater clocked out a duplicate signal so the hard-of-hearing device could have a fresh signal just 2-feet away.
As with Bruce, I often step down my coax when just working within a rack. I don't normally do Broadcast racks though (or trucks). For Analog video using single coax, I will use something like West Penn 818 or Belden 1505F. They are ultra-flexible cables that route really easy and deal with things that tilt or pull-out...etc. However, you don't want to do long runs with them as they are stranded type cores with notably poorer HF response.
For other forms of analog...I will go down to much smaller coax, depending on the run and signal type. Belden 1164B is a popular one for us in component. It fits both RCA and BNC crimpers real well. The only thing I don't like about it is that its overall jacket is pretty thick and it has filler cords so it is 1/2" in diameter for a 3-core cable. For 5-core cable, we use Extron's Mini-High-Res (MHR). It is real easy to work with, fits under a typical HD15 hood and can adapt to RCA or BNC. Its frequency characteristics are pretty impressive for its size. Extron also has things like boots for the cable so you can "ruggidize" the end for field use.
Which brings me to RCA vs BNC...if we know the device will use an RCA connector, then yes, we will install RCA connectors...depending on the cable, that will be solder or crimp (and possibly compression crimp). If we know the end user will be handling the cable a bit...they will be soldered.
Yes, RCA to BNC adapters can (and are often)used they should not be the goal. Each connection point is a point for signal degredation. Also such adapters can often lead to cables that merely "pull out." BNC connectors are also the only ones that give you a chance at extending a cable and keeping the impedance correct. If you use the proper BNC connector the signal as it passes through the BNC connector should look the same as if there was no connector...the same can not be said of an RCA or even the HD15 used for "vga" connectors.
Steve
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