|
|
 
|
|
Author
|
Topic: Length of HDMI cables
|
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 11-05-2007 12:16 PM
3-meters is the spec on DVI or HDMI cables. That said, there are certainly longer cables out there that are working but anything beyond 3-meters and you are taking chances depending on the components used, signal type, and the cable quality.
There are means to extend that cable length but there is a cost associated with it. One method uses Cat5 or like cables to extend the length using propritary transmitter/receivers. For instance, Extron has their HDMI 201 which will allow you to get 1080i and less signals up to 200-feet and 1080p signals up to 100-feet. List price for the set of boxes is $810.00 though the street price is somewhat less. I've used it on a long run and it works quite well...plus it also allows one to extend the RS232 signal as well.
As to your other questions...
Signal wise...it is digital versus analog. Good analog will compare to good digital very favorably if all else is equal. However, one thing I'm seeing again and again with analog signals is that the sync pulse on the higher resolution signals is of the same order as a light to dark tansition of the video signal....as such, when there is a light to dark transition (Think camera flashes and such), the projectors or other devices might lose sync mometarily and flash the screen. Digital does not suffer from that. If the source is a digital image, the digital signal has the potential to be sent to the display exactly as it was stored. There is also a handshaking that is done with HDMI/DVI such that you should get the highest resolution that both devices understand. Lastly, HDMI may be the only means you can show 720p and up signals on some devices due to copy protection. That is, if the media is utilizing HDCP, then only the HDMI output is likely to have HD available. The Component outputs may be limited to 480i.
As for making the cables...they are not condusive to being field made at this time or I'm not aware of them being suited for field termination (or DVI). When they are, I plan to be able to terminate them the way we do other video/audio signals.
Steve
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 11-12-2007 08:29 PM
There are typically two things that kill signals...resistance (signal strength goes down) and capacitance (HF signals attenuate at a greater rate than the resistive losses). Thus, yes, larger cross-sectional copper will do better in the resistive department, but cable construction/design is how one does better in the capacitance or impedance matching department. Generally speaking, the higher the signal quality (1080p versus 480i), the higher the frequency of the signal on the cable and thus capacitive effects play a very big role.
I've seen botched DCinema installations where the installer used an analog audio cable for digital audio...sure it will work on short runs but as the runs get longer, one MUST use 110-Ohm cable and that is not the typical audio cable. The stupid thing was that it had a DoReMi tag on it...THEY should know better. I think they were using Belden 1510C (analog audio snake) instead of 1803 (AES-EBU audio snake). For a 6' run, it doesn't really matter...but as the run turns into 10s of feet, the signal degrades geometrically with the distance.
Looking at 1510C a bit closer (using its spec sheet), it has no intrinsic impedance rating. It has a 31pF/ft capacitance conductor to conductor and 58pF/ft capacitance conductor-to-conductor-shield.
Now, compare that to 1803F. It has a 110-Ohm intrinsic impedance, with only 12pF/ft capacitance cond-cond. or 26pF/ft cond-cond-sh.
Note, both cables read the same...4-pair snake, 24awg conductors...etc...only when you look at capacitance and overall size do you start to see what the big differences are. Note to the 1803F, they list the attenuation the cable presents by frequency over 100'...so, for example, it will attenuate a 24.576MHz signal by 3.08dB over 100'. No such rating exists for 1510C. After all, it is audio cable...nobody much cares what it does over 20KHz...and really could care less at 24MHz.
But back on topic...the cable is a big player in getting good results over longer distances...but for 3-6' runs damn near anything will do so long as the connections are good.
Note too, the connector type can also limit your signal. That is, you may take a signal "hit" just due to the connector type. This a problem with HD15 connectors as used for computer signals. The HD15 is not a 75-Ohm connector and will cause reflections at higher frequencies. BNC connectors can be made to 75-Ohms (or 50-Ohms for other applications) and thus will pass the signal with almost not signal degredation.
I highly doubt that either DVI or HDMI connectors are particularly good at preserving the signal as it already has a length specfication using those connectors (3-meters). Also presumably, once a signal reaches its destination, it will be "repeated" out with a fresh copy of the signal rather than any sort of passive switching.
Steve
| IP: Logged
|
|
|
|
All times are Central (GMT -6:00)
|
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Printer-friendly view of this topic