HD over Coax

[tedanderson]

Given that many of the local television stations are able to broadcast in HD over the airwaves and they can be received by anyone with an HD television set and a standard external UHF antenna, is it possible to be able to do the same thing over standard coax cable in a closed-circuit type of situation?

Does anyone sell any kind of modulator or device that will transmit the HD signal from the HD source to the HDTV via coax cable?

Currently our church has several remote viewing locations throughout the facility and little-by-little we have been swapping out our older tube TV's for plasmas and LCD's that have HD capability. We have been reconnecting the original coax cable due to the fact that its convenient and cost effective. But the bad part about that is that using standard definition on a flat panel does not look that great unless you are watching from a distance.

So the other day I thought that if its possible for the local TV stations to broadcast over the air in HD, then why can't we broadcast in HD through our closed circuit system via the coax cable. It's pretty much the same principle but I have not seen anyone doing it. Every other HDTV church system that I have seen has been done via the 5 analog coax cables with this MASSIVE distribution cabinet feeding all of the screens.

[Gracetech]

I've been recently looking in to this for future plans but all i've come up with so far is that the industry is just really behind right now. What you need to feed a ATSC tuner is a ATSC modulator which is actually a MPEG 2 encoder+Modulator. I've found a few leads on these but most are hopped up computers instead of the good ole rack RF modulator. I assume that any computer loaded with a 8VSB PCI Modulator card can do what we need in broadcasting. I'll add to this thread as i find out more.

Check this out.

crt

Some more links
http://www.teleview.com/?module=Good...Mode=VIEW_FORM
http://www.teleview.com/?module=Good...Mode=VIEW_FORM

[GQmacguy]

This might be a little off subject, but at CES Gefen demoed a HDMI-over-Coax solution that they said will be ready in April. That might be an option if it is just a (inexpensive ) little box that converts your source signal to coax and then to your locations.

Gefen Press Release

Gizmodo Source Post

[tedanderson]

Inexpensive would be great but I am prepared to take the figures to my leadership regardless of the cost. I will also need to spec out an upconverter which probably won't be cheap either but I am sure that everyone will appriciate a clear picture on the flat panels.

Generally, I don't know if I am just more technically inclined than most other people but I don't know how people can look at a flat panel with the blocky images and comment on how great it looks. Once they eventually upgrade to HD (through their cable company) only THEN do they see the difference. I don't know if the novelty of a flat panel is what has people snowed into thinking that its a clear picture or whatever, but certainly they have to notice that the blocky image on the plasma is not as clear as the one on their regular tube TV. And even though it will not be a high def signal, it will still be better than what we are getting now.

[billmi]

Perception is a lot of it. Back in the 80s, Sony did consumer tests with HD, and something like 90% of the test subjects thought that SD footage was sharper and higher resolution than HD footage when the SD footage was accompanied by surround sound and making use of the subwoofer.

Satellite and Cable companies rave about "digital picture quality." Sure, it's a sharp picture - but it's also full of blocky compression artifacts.

As for scalers, I'd be personally more inclined to shop for displays/projectors that have a good scaler in them to start with rather than pay for two scalers - a poor one in the display device, and a good one to replace it.

[DTV-Engineer]

This is slightly oversimplified overview:

1) The standard for high definition serial digital video over coax is called SMPTE 292M; this is properly called HD-SDI (High Definition - Serial Digital Interface). It operates at 1.485 gigabits per second, is uncompressed, and can transmit any of a number of formats (e.g., 720p, 1080i, etc.). A cable carrying SMPTE 292M will have one, and only one, program stream.

2) The actual data transmitted over the air is governed by SMPTE 310, which specifies a 19.39 megabit per second data rate; this data includes one or more MPEG-2 program streams plus data which identifies the programs and other operating parameters (this additional descriptive data is called PSIP). Obviously, there's an enormous amount of compression happening to fit 1485 million bits of raw video and audio into a 19 million bit stream!

3) The over-the-air signal itself -- that is, the RF -- is generally specified as "ATSC". Among other things, ATSC calls for SMPTE 310 data, modulated 8VSB, occupying a 6 megahertz bandwidth channel.

In order to transmit high definition video as RF -- it doesn't matter whether it's over the air or through a cable -- you need:
- A SMPTE 292M program source,
- A high definition MPEG-2 encoder that generates SMPTE 310,
- An 8VSB ATSC modulator.
This assumes that the encoder is capable of generating static PSIP... if it doesn't, you also need a PSIP generator and multiplexer.

Not so simple, is it? It's also not cheap: the encoder alone runs upward of $35,000, last I checked. (You're looking at something like a Tandberg E5821 or a Harris Flexicoder here.)

As a practical matter, you can get an awful lot more bang for the buck by
processing and distributing video as SVGA: it can be either 4:3 or 16:9, it's progressive scan, and the resolution is comparable with HD. The only practical limitation is distance, and our church runs SVGA over category 5 cable at least 300 feet from our worship center to a gym. Oh, and you can plug SVGA into just about all projectors, LCD and plasma displays...

-- Jeff

[tedanderson]

From what you are telling me, this seems to be much simpler than I thought it would be. Obviously you can't just walk into your local Radio Shack and ask them for an ATSC modulator But now this gives me a much clearer understanding of what I will need when I hire the consultant to do the work. So even if this setup ends up costing us the better part of $100,000 in the long run it would still be a worthwhile investment being that we have the issues of distance and multiple screens.

Our facility is about 1200 feet from end to end which puts us close to that figure in cabling distance from our production room to the furthest point away. In addition to that we have 44 screens throughout the building and over half of them are projectors, EDTV or HDTV flat panel screens. It's likely that all of the tube TV's will eventually be replaced with flat panels as they start to go bad.

So I figure that coax is the most efficient and trouble-free way of delivering the signal. When I need to add a TV, doing a coax split is much easier than home running an SVGA cable more than 500 feet. In addition to that, splitting SVGA is probably not cheap either. Granted a 16 port D/A for SVGA and all of the repeaters and cabling is still cheaper than getting the encoder, upconverter, and the ATSC modulator but my degree of troubleshooting will be much less of a headache.

Another thing that I consider is that even though we will have mostly projectors and flat panels, there will still be plenty of tube TV's in our facility so I would like to minimize the degree of a "mixed environment". We are always changing and re-arranging our setups and sometimes we have situations where we swap out a flat panel for a tube TV and vice versa. If everything is running on coax, it's not a hard thing to do. The only exception would be the projectors which do not run on RF, however a demodulator or a VCR would be sufficient for that application.

[DTV-Engineer]

Originally Posted by tedanderson

From what you are telling me, this seems to be much simpler than I thought it would be.

Funny, I thought I had made a pretty good case that this was an impractically difficult and expensive way to solve this problem!

I think you would be wise to take a step back here... this is precisely the same kind of decision we wound up facing a year ago during our last building expansion. Because my professional environment is broadcast video, I think first in terms of traditional broadcast solutions. What I had to do was ask myself some really basic questions about the system objectives that finally led me to a surprising change of approach.

The first question was, what kind of displays am I trying to drive, and what is their capability? It turned out that the most critical displays were projectors, followed by plasmas. Both are very happy playing SVGA, which after all is up in the same resolution range as 720p HD. We also wanted to feed analog televisions, VHS and DVD recorders.

The second question was, what are our video sources? In our case, NTSC cameras, DVD with component output, VHS with S-Video output, and several computers with SVGA. We also wanted to handle HD video in the future.

Ultimately, I realized that the most effective solution was to make our plant VGA-centric; the equipment is readily available and fairly inexpensive; it preserves the quality of our best sources straight through to our best displays; and it is easily converted to NTSC for in-house cable and recording. Our worship center has two Kramer VP-727 scaler/switchers: one for projection / IMAG, the other for a live feed to other rooms and recording. We even have a cheap VGA switch that lets us control stage monitors and a plasma on the back wall. The Kramers accept any video format we throw at it and convert it to VGA for internal processing. We take the VGA outputs and use CAT-5 splitter / extenders to get the feeds where they need to go; we also use a middling scan converter to produce the NTSC feed.

Okay... that was how we resolved the issues, and it has worked incredibly well for us. Your needs may well be different, but I still suggest approaching the design by letting the objectives determine the "how to", rather than assuming that the method is a given.

If it turns out that you still want to use HD-SDI video -- that is, broadcast-style SMPTE 292M -- as the origination and switching format, I would say that there are more efficient ways to distribute it than via RF. If you're simply distributing a single program feed around the building, the best shot would be to break your facility into zones and run fiber from your control room to each zone; each zone has a wiring closet where you convert from fiber to coax and hit a reclocking distribution amplifiers to go the final distance to each display. You will be limited to about 350 feet of Belden 1694A coax to each, but that shouldn't be terribly restrictive. For displays that already have HD-SDI input, you're all set; or, you can tack an AJA HI5 adapter behind your monitor to convert the video to HDMI.

There are many benefits to avoiding encoding and modulating schemes, besides cost... for one thing, the picture quality is much better. In a "live" application, encoding the video means that you are building in about a full second (or more) of delay; by comparison, distributing uncompressed 292M incurs no delay at all. You can still down-convert one of your 292M feeds to NTSC and drive an analog modulator to feed your legacy TVs...

(If I had the money you apparently have access to for this project, I would home-run all of the "important" displays back to the control room, and feed them from an HD-SDI routing switcher... extremely flexible, no delays, perfect quality video.)

I'm imagining that your consultant, when you get to that point, will probably try just as hard to dissuade you from building an ATSC plant as I am... really, it spends an awful lot of money, degrades the picture, adds a whopping amount of delay, and yields a very difficult system to troubleshoot and maintain. And it effectively spends most of that money to distribute only one signal.

Run, while there's still time!

-- Jeff

[tedanderson]

If you think that building an HD tv station in the control room is a bad idea, I will take your word for it without any need for further explanation.

I was hoping to be able to do this with a coax infrastructure for all of the remote viewing locations to minimize the difficulting in installing or troubleshooting new TV's or monitors. Our existing infrastructure is 99% RF which works very well and it is very easy to troubleshoot and isolate problems. The only thing that is really bothering me is the blocky images on the flat panels that do not have internal upconversion for a standard NTSC signal. Some of our plasmas look great with a standard signal and other look not-so-hot unless you plug in a high def signal directly into it.

[START RANT]
Ultimately the solution would be to purchase displays that have this capability, however, we are not the ones that get to spec out the equipment when the decision is made to purchase a flat panel. Without notice or warning, the leadership will decide that they want to put a 50-inch plasma in a particular location and then call me to install it after it arrives at the church.

I had one situation where a leader asked me why the picture was not as clear as it was in the store. As much as I attempted to explain the reasoning, this individual was certain that it was something that I did wrong while installing it. He said, "We payed good money for this TV! This picture should be crystal clear!" and as more people are upgrading to HD at home, they will come to church and see the difference.
[/END RANT]

So overall I thought there might be a solution to getting a clear picture on non-upconverting TV's via the coax but I think that I will look into running the fiber in zones. This was my initial plan to recable the facility with RG-6 by running a 4-inch conduit down the length of the back alley so that home runs can be distributed at strategic locations at each building on the campus. And then at each building or pair of buildings would share an amplified splitter.

[DTV-Engineer]

Originally Posted by tedanderson

If you think that building an HD tv station in the control room is a bad idea, I will take your word for it without any need for further explanation.

Let me be clear what I'm really getting at... I have no problem with building the control portion as HD -- in fact, there are some big benefits in terms of real-time switching and graphics insertion. What I'm addressing is how that signal is being distributed around your plant to the use points.

You might take a look at Evertz for a really good example of how this could be done well: their 7700 series is a rack-mount frame which you populate with up to 15 cards, according to what you want to accomplish. Let's assume that you have a frame at your main control point, and a frame in each zone.

In the control room, you would feed your main SMPTE 292M program feed to a 7700DA8-HD, which gives you eight reclocked copies of the signal. You'd also have a 7705EO-HD electrical>optical converter for each zone, each being fed from one of the DA's outputs.

Each zone's wiring closet would have a frame with a 7705OE-HD to convert from the incoming fiber back to coax, plus as many 7700DA8-HD distribution amplifiers as needed to feed the monitors / projectors.

See how easy it makes things? Each step in the chain reclocks the data, which essentially stabilizes it, removing jitter and restoring signal level. Reclocking does not add a significant amount of delay (less than a microsecond), and in any case the audio is embedded into the video, so there isn't a lip sync issue.

There are all sorts of neat converters and other functions you can plug into these frames... even cards that take a bunch of video feeds and combine them into an integrated display for a monitor wall using only a couple of plasma monitors.

Check them out on their web site here.

-- Jeff

[benwilhelm]

Why not use a HD over Cat5 solution? I saw one the other day from CE Labs. Check out Cat5 Distribution here: http://www.cable-electronics.com/pm/index.html

Just a thought,

Ben

[DTV-Engineer]

Originally Posted by benwilhelm

Why not use a HD over Cat5 solution? I saw one the other day from CE Labs. Check out Cat5 Distribution here: http://www.cable-electronics.com/pm/index.html

Just a thought,

Ben

Interesting... unfortunately, broadcast grade HD video isn't typically transmitted as analog Y/R-Y/B-Y... that's more typical of standard definition professional gear (e.g., Betacam) or consumer HD. Typical HD studio equipment uses a single coax for digital component, running at around 1,485 million bits per second... and it includes not only the video, but also embedded audio and other metadata.

The biggest practical difference is, analog video deteriorates as the transmitted distance increases; notice that the apparent limit on the CE box's cable comp knob is 500 feet. Even with compensation, you will see noticeable distortion in the video. Digital also has distance limitations, but there's one huge difference: so long as the receiving equipment can recover the data, it doesn't matter how long the run is: the far-end video will be absolutely identical to what had been transmitted. For instance, you can run uncompressed HD-SDI more than 300 feet over Belden 1694A coax... if you hit a distribution amplifier with a reclocking input, you can go another 300 feet. In fact, you can keep going indefinitely so long as the maximum length before reclocking in any one hop doesn't exceed about 300 feet... and the far end video will still be identical to what you started with.

There are other compelling reasons for using HD-SDI in a production and transmission environment... you aren't going through multiple analog/digital conversion steps, you don't need to worry about Y/C delay from mismatched cable lengths... but mostly, it's much easier to work with and far superior in performance.

As a rule, our experience is that equipment that uses RCA connectors for video -- especially for HD -- isn't broadcast grade.

-- Jeff