RGBHV over shielded Cat 5 success!
I am currently typing this message using a 25ft
shielded cat 5 Ethernet cable. The image is extremely clear noticeably better
than my 30 foot bundled coax that I normally use. To make the test more
difficult, the Cat 5 cable is actually two separate pieces with a junction box 6
feet away from my monitor. This will be the cable that I will use as my HT
redesign reaches final completion.
The idea actually came from Thumper.
Dismayed by the price of plenum or standard rated coax cable and video
amplifiers for his installed, he started tinkering with the idea of using
Ethernet cable to run his video signals. He shared his success with me
He
told me that I could get good results with standard Cat 5E cable and outstanding
results with shielded Cat 5.
Well, premade shielded Cat 5 cables are a
little hard to come by so I first tried the experiment using unshielded cat 5. I
bought a 25 footer cut it into two 6 foot and 19 foot section and put an HD-15
on each of the cut ends. I then put an in-line Ethernet splicer to join the two
Ethernet ends (explain latter). This yielded a long HD-15 to HD-15
cable.
Well the results with this cable where far from stunning. I got
plenty of ringing and blurring at most frequencies including really bad results
at 60 Hz.
I explained my results to Thumper and he told me to redo it
with shielded Cat 5. I was very skeptical because I wasn't having a noise
problem but ringing (i.e. impedance mismatch) problem instead.
That's
when it hit me; general Cat 5 is 100 ohm twisted pair; however, with the shield
tied to ground on the shielded version this would help lower the impedance to
closer to video's 75 ohm requirement. I decided to give it another
try.
The construction details:
The only local place I could find
shielded Cat 5 products was at Fry's. L-com has them but they are mail order and
a little more expensive.
I did the exact same thing as before. I bought a
25 foot shielded cat 5 cable and cut it into a 6 foot and 19 foot piece. I also
bought a shielded Cat 5 junction box, two HD-15 male solder cup plugs and to
9-pin metal hoods (HD-15 is the same size). I wired the HD-15's in the following
fashion to the shielded cat 5 cable.
HD-15 pin Cat 5
color
-------------------------
1. Red + Orange
2. Green + Green
3.
Blue + Blue
4.
5.
6. Red - (aka GND) Orange stripe
7. Green - (GND)
Green stripe
8. Blue - (GND) Blue stripe
9.
10. Ground (GND) shield
wire.
11.
12.
13. H sync Brown
14. V sync Brown
stripe
15.
The "-" signals are actually the very same ground as
"Ground" is. The H and V don't need their own separate ground line. The results
were excellent as I stated before.
At this point you might be saying
cool but what does shielded Cat 5 give me over bundled coax? It gives a few
things:
1. Thinner form factor.
2. Cheaper cable. Plenum being much
cheaper
3. Much easier to solder to an HD-15 connector. Bundled coax requires
shield terminators when soldering and big mouth back shells to allow the larger
diameter of the cable to exit.
4. similarly, no break-out BNC to HD-15 cables
required. These bring their own problems
and my favorite,
5. It
allows me to manually switch four RGB sources between 2 displays. This would
normally require a matrix switcher which is usually $1000+. To do this, I have
two Ethernet jacks (one for my UP-1100 and one for my Princeton Graphics
monitor) and four cables (HTPC, AccessDTV, Digital cable and Dreamcast) that go
in in any configuration that I want.
All of this with an outstanding
video quality to boot. This is really cool.
Thanks Thumper,
-Mr.
Wigggles
------------------
The Mothership is now
boarding.
[This message has been edited by MrWigggles (edited
06-12-2001).]