|HDTV - Way cool looking TV|
THIS PAGE IS UNDER DEVELOPMENT
|Introduction - a very quick overview|
|What's available and where in HD|
|Dish Network's HD modulator. Pictures are also available here|
|Dish Network HD modulator FAQ|
|Some HD "screen grabs"|
|Links to HD related sites|
First, let me say I'm not going to explain how terrestrial digital TV works - if you want an overview of how this is done, look at my North American MPEG-2 Info page. Although this page is all about satellite based MPEG-2 video, virtually all the terms there apply here - all the principles are the same, just the method of delivery is different.
The world is making the wonderful transision to digital TV. One would have thought that since the world has evolved three different analog TV systems (with many different flavors of the three), this would have been a great chance to unify the world with one TV standard. Alas this didn't happen and we now have three competing DTV systems:
|DVB-T||Europe, Australia||COFDM||DVB||MPEG-1 Layer 2 and/or AC3|
|ATSC||Canada, US, Taiwan||8VSB||ATSC (Digipher 2 like)||AC3|
All three systems are based on the MPEG-2 video system but use widely different modulation, systems and audio formats.
MORE WORK NEEDED HERE
What's available and where in HD
Currently, the only country in the world that's broadcasting HD video is the United States and currently this is sporadic.
On the terrestrial front, since the FCC mandated that the top 30 markets must be covered by DTV transmissions by November 1999, the roll out here has not actually been forced by market pressure, but by governmental control. As a result, there is little knowledge of DTV in the United States and as a result most video is broadcast in SD with only special events and "prime time" programming in HD.
On satellite, both Dish Network and DirecTV offer HBO-HD East. Currently, around six movies a day are transmitted in HD. DirecTV also plans to offer a PPV HD channel, but this isn't on air yet.
Time Warner cable in NYC also has HBO-HD on their cable system by using a regular 8VSB signal mixed into the cable.
Showtime and Discovery have said they plan on launching HD channels in 2000.
Dish Network's HD modulator
When designing satellite (or cable) set-top boxes that are HD compatible, the designer has two choices: either design a new receiver that contains an MPEG-2 decoder capable of both HD and SD or by using the MPEG-2 decoder available in the HDTV receiver - which is inherently HD capable.
There are advantages and disadvantages with both methods. An integrated HD box means that the program guide and other satellite related displays can be overlaid on top of the HD video but because two HD decoders are part of the system (one in the TV and one in the satellite receiver), there is obviously a price penalty since HD capable MPEG-2 decoders aren't cheap yet. DirecTV is taking this aproach for their first generation HD compatible set top boxes. Actually, the way RCA is putting together the package is that the satellite receiver can receive regular DirecTV and HD DirecTV along with terrestrial 8VSB signals. The output of this receiver then feeds into an analog-only projector which also does the NTSC work.
Echostar chose the other approach for their Dish Network system - designing a transcoder that simply remodulates the MPEG-2 Transport Stream onto an 8VSB carrier so it can be received and decoded by the TV. This technique results in an inexpensive adapter board ($300 is expected to be the going rate) but has a the negative consequence of prohibiting the satellite receiver from doing any form of on screen graphics when the system is in satellite HD mode.
Echostar's high-end receivers (like the 5000 model) have a parallel expansion port that outputs the entire transport stream decoded from the QPSK carrier (which came from the satellite) but with the currently tuned program unencrypted. This parallel transport stream is then stripped of everything but the active program and then regenerated as a 8VSB signal moduled onto an RF carrier which is then tuned by the VSB tuner in the TV.
The really spiffy thing about what Dish Network is doing is that they're making an ATSC MPEG-2 Transport Stream from a DVB-S MPEG-2 Transport Stream. This is done with a ASIC (Application Specific IC) in the ATSC adapter - it generates the ATSC-SI tables allowing reception by an ATSC TV device which of course uses different Systems Information than the DVB-S signal coming from the satellite. The ASIC is also the hardware that's responsible for removing the PIDs that aren't used and stuffing NULL PIDs to keep the resulting 19.6Mbps data rate that the ATSC system uses
Pictures of the Dish Network HD modulator
Click to see full size.
|Top view of the modulator|
|The Accessory connector is used with an IR transmitter to blast the commands to your ATSC TV|
|Inside the modulator. The chip at the top center is the 8VSB modulator, the Altera part is a custom gate array and the chip at the bottom labelled X100 is a Flash memory - I assume it contains the extra code for the receiver to operate the modulator.|
|Hooked up to the back of the model 5000 receiver|
Don't agree with the message, but the picture looks pretty damm
Keep in mind that the picture was taken with a 1024x768 digital camera that uses JPEG compression - the real thing looks much better!
Dish Network HD modulator FAQ
You what? What's all that PID mumbo-bumbo about? What exactly does the HD modulator do?
Put simply, it allows an Echostar 5000 receiver to receive High Defintion TV from the Dish Network DBS service. To receive the HD signal, an ATSC tuner and compatible display are required. Dish Network currently only offers HD on their Echo 3 satellite at 61.5° West. Since this is a special-use satellite, if you also want regular satellite programming, you'll need multiple dishes and switching equipment.
I have an HD capable display, but no ATSC tuner. Can I use this setup with the HD modulator?
No. The output from the HD modulator is RF, so equipment is required to receive the digital signal and decompress it using MPEG and Dolby Digital decoding equipment - equipment otherwise known as a set-top box.
What! RF? I used that to copy a video tape once and the result was terrible.
This is the wonderful thing about the digital world - even if the bitstream is sent over RF, as long as the signal doesn't get mutilated, the resulting bitstream is identical.
How do I pipe Dolby Digital into my audio equipment?
Since ATSC has DD (Dolby Digital) as it's native audio format, your ATSC tuner outputs DD to your receiver for processing. This applies not only to HD but also to standard definiton PPV in DD format. The DD PPV movies I've seen using the ATSC MPEG-2 are superior to both the composite and s-video outputs from the 5000 receiver since the display input is component format.
My ATSC TV isn't listed as seamless in the manual. How should I setup for off-air?
There are two ways. The first which Echostar recommends in their manual, is to feed the off-air antenna into the HD modulator's input and then to program the DTV channels into the list of local channels. When the receiver is tuned to channel 861 (HBO-HD East) or a DD PPV, the receiver will output the HD signal onto RF channel either 3 or 4. The antenna input gets switched off just like a VCR does when you turn on the VCR's tuner.
To switch to an off-air DTV station, you then tune to a local DTV station programmed into the 5000 and you'll hear a relay click inside the modulator, at which point the antenna is connected through to the ATSC TV and you can then use the ATSC tuner to select the channel you want.
The other approach results in more seamless operation, provided all your off-air DTV stations are in the UHF band. It involves taking a simple RF splitter, connecting one of the common connectors to the antenna and the other common to the output from the HD modulator. The single connector is then routed to the ATSC TV.
Using this connection technique, when an HD program or DD PPV movie is tuned on the 5000, this signal can be received on channel 3 (or 4) and all the other off-air ATSC signals can be received at the same time, making it trivial to surf between DTV channels and the output from the satellite receiver.
If you're in an area where there are DTV stations in the VHF band (channels 2 through 13), this combination probably won't work because of inter-signal interference from the VHF stations being received via the antenna. There are devices available, designed in the days of analog TV that merge a channel 3 signal into coax, but letting all the VHF/UHF signals through (other than channel 3 of course). I haven't had a chance to try one of these devices yet with ATSC - if you have, please drop me a line.
I have a Panasonic ATSC set top box and a Panasonic DVHS VCR. Can I record with this setup?
Yes. The STB receives the ATSC bit-stream, sends it over the firewire to the VCR and then plays back via the firewire without problem.
Here are some screen shots of the HBO HD promo loop. These were captured by taking the MPEG-2 video stream from Dish Network's Echo 3 satellite at 61.5 west and then feeding it to a PC using the SCSI data transfer capabilities in DVB2000. The video stream was then decoded with a software based MPEG-2 video decoder - obviously at much lower rate than real-time.
The source material was in the 1920x1080 format, but was converted down to around 1268x712 since my monitor operates at a maximum resolution of 1280x1024. Click on the images to see them at maximum size.
|Men in Black. This is with a doubt my favorite capture. It never looked that good at the theater!|
|L.A. Confidential. You really get some depth perception because of the resolution.|
|The Fith Element 1. The banding that shows is probably due to the down convert to the odd display size as a result of my monitor. Funny - on the DVD version, this shot looks more realistic. The higher resolution shows a weakness of the graphics rendering system used to generate this scene!|
|The Fith Element 2. Same problem with this shot.|
|HBO blurb. Have to give them credit for being a very good SDTV movie network. Can't wait for their HD channels!|
HBO Original movie "Gia". My second favorite shot.
The contrast in the capture is incredible.
Thanks to Chris Williams for IDing the movie.