I have coax cables for VGA/Component run in my ceiling to my projector. I do not have a HDMI cable run but wonder if there exists a converter that will go from HDMI to coax and then back so that when I upgrade to a better projector with a HDMI input I can use the coax cables to send the HDMI signal. I believe that the HDMI uses differential signalling so I'd imagine the converter would have to have baluns in it. Additionally, I have a total of 8 coax cables (5 for VGA, 3 for component) and wonder if that is enough for all the critical HDMI signals.


Any experts with an opinion on this?


Thanks,
John

That might be a tough converter device to find because there are legal issues with converting from HDMI's encrypted digital signaling to unencrypted analog over coax. Technically, it could be done if it's for content that does not require content protection, but it's not likely that we'll see such devices on the market due to the limited usage for lower resolution content.

The device would not be converting digital to analog. It would be taking the analog waveforms encoding the digital information and passing them though coax cables instead of the HDMI cable.

John

John,

If you do not need the audio to pass to your display, there are several A/D converters on the market.

DCP261 VGA/Component to DVI (http://www.digitalconnection.com/products/video/dcp261.asp)

DC-AD2X VGA to DVI (http://www.digitalconnection.com/products/video/dcad2x.asp)

You'll need a DVI to HDMI adapter using either devices.

He just wants to send the HDMI signal down his existing cables. He's not looking to convert the HDMI signal.

He just wants to send the HDMI signal down his existing cables. He's not looking to convert the HDMI signal.

The device would not be converting digital to analog. It would be taking the analog waveforms encoding the digital information and passing them though coax cables instead of the HDMI cable.

I guess I misunderstood him when he said he wanted to take analog waveforms and encode to digital, which I took to mean he would start with analog signal. Unfortunately, I can't think of how he can mimic twisted pair with his coax cables. Wireless maybe his only option.

3:29 am... early bird gets the worm, unless the insomniac bird beat them to it. ;)

So the actual question I have is what exactly is the legal basis for this? I would assume that we are talking about the HDCP (DCP LLC) agreement. Does it prevent an analog 1080i/p output from a device with a HDCP encrypted input? An analog output would not necessarily create a 'perfect digital copy'. Also since DVI+HDCP to analog VGA convertors exist outside of the US in the gray market, it would be fair to say the allowing them in the US would not contribute to copyright problems, and would also allow some innovation on hybrid products in switching and distribution. Also with Blu-ray and HD-DVD rips now being shared on the net, I would think the HD 'analog hole' is even less of an issue than ever.
So HDCP people, what are the chances of a allowing these to exist?

Let me clarify. The digital information that is transmitted over a HDMI link is transmitted as an analog waveform over differential pairs. Without encoding/decoding or changing the digital information in any way, I simply want to run the analog waveforms though coax instead of the differential pairs of a normal HDMI cable. This can be done using a type of transformer called a balun to go from differential to single ended on one side of the cable and then from singled ended to digital on the other side of the cable. I don't know how many differential pairs and other single ended signals exist in a HDMI cable and any requirements such as allowable transmission time skew between pairs so I don't know if the 8 coax cables I have are enough. Additionally I don't desire to wire this up myself if there exists a product somewhere that already does this.

This can't be a legal digital rights issue here. There is no demodulation, decoding, deencryption or anything going on here. There will be a HDMI connector at each end of this , only the wires inbetween the connectors will be changed from differential pairs to singled ended coax by using balun transformers.

There seems to be a confusion about digital versus analog. All of the signals in our "digital" equipment are analog waveforms that represent digital information based on their levels. The digital information over an HDMI cable is sent via analog waveforms. This is completely different than converting a digital format broadcast into an analog format such as component or VGA.

Kei,
Thanks for the thoughts on the DVI/VGA converters. I don't actually want to convert from DVI to VGA and back as I discuss in the previous post.

...I simply want to run the analog waveforms though coax instead of the differential pairs of a normal HDMI cable. This can be done using a type of transformer called a balun to go from differential to single ended on one side of the cable and then from singled ended to digital on the other side of the cable.

What you are asking for is not technically impossible, and it certainly would not cause any legal troubles. The problem is transformers are not perfect devices, and have some loss. So passively converting from differential to signal ended, and back again, would have more loss than just dealing with the loss of the twisted pairs.

A properly engineered solution could have a differential receiver to a single ended line driver with proper pre-emphisis, some high frequency coax cable, and a matching recevier system. There would need to be 4 coax runs, plus I think about 11 other wires for low speed data and power. Could be done, but from a product designers perspective, HDMI repeaters/extenders might be a more cost effective solution.

Sorry I misunderstood the original post. Yes, it's certainly possible to convert HDMI signals from the HDMI cable medium to other physical mediums such as Cat5 cable, optical, or coax. There are products on the market that do this conversion to and from Cat5 or optical already, so coax would be just another media to throw into the mix.

Get yourself 4 pairs of "broadband balun", let me know if it works. Search google. I found them as low as $60 each. 5 more conductors are needed as a minimum. This will not include the audio. I'm looking for the same thing. Or try the Video Ease I from muxlab. Looks like it has passive baluns for 3 pairs to 3 coax. This all doesnt look practical. I might be doing plaster work again cause I am thinking of running a new cable. or Extron Model DDTX DVI & DDRX DVI.