Question for Engineers or GMs about Subchannels

[Tom Snyder]

Question surfaced on Twitter. We all know that bandwidth-sucking subchannels cause motion artifacts on sports and other fast motion programing on the main channels.

When the TV stations send their programming to TWC, U-Verse, D*, etc., for rebroadcast are they sending the signals through a single fibre/cable that forces the same limitations, or can/could they send it full bandwidth, uncompressed and eliminate the pixelation that the OTA signal forces us to contend with?

[tencom]

Question surfaced on Twitter. We all know that bandwidth-sucking subchannels cause motion artifacts on sports and other fast motion programing on the main channels.

When the TV stations send their programming to TWC, U-Verse, D*, etc., for rebroadcast are they sending the signals through a single fibre/cable that forces the same limitations, or can/could they send it full bandwidth, uncompressed and eliminate the pixelation that the OTA signal forces us to contend with?

I used TS reader, to check the data rates for many  OTA  streams, on cable and found that they were about what they were over the air so it appears that  the broadcasters, sends the same data to  TWC for their distribution and since TWC uses MPEG 2, which is the same that OTA uses, and U-VERSE and satellite use MPEG 4 AVC which could get by with a lower data rate then MPEG 2. TWC remains as the only source to confirm wether or not that others get a full bandwith feed but appears unlikely.
You should also know that  not only is there motion problems with over-compression but spacial ptoblems which means that much detail is removed And the less detail to describe  means you can reduce the data rate. In fact if you carry spacial compression to far you can have people with blank faces which did happen in the early days, with Direct TV.

[Rick_EE]

I was told by an employee of channel 4 that DirectTV and TWC get their signals OTA.  It appears that TWC and DTV had to pay to maintain the feed, so they went OTA as a cost cutting measure.

Hopefully they reconsider.  Though I noticed that the ESPNHD coverage of the game last night had a lot of the issues I saw during the Packer game.  Maybe it is a TWC issue now.

I have to say that the packer game on 8/29 was a lot better than the one on 8/15.  None look a crisp as they did last year.

[John L]

I was told by an employee of channel 4 that DirectTV and TWC get their signals OTA.  It appears that TWC and DTV had to pay to maintain the feed, so they went OTA as a cost cutting measure.

When we had that bad storm 2 months ago it knocked WTMJ-DT transmitter off the air for a day or so. While it was OTA, WTMJ-TV was broadcasting over TWC cable with no problems. Therefore I don't believe TWC receives WTMJ-TV/DT OTA...very much fiber Optic Cable direct from the studio.

-John L.

[Rick_EE]

The employee is a friend of mine.  I believe him.

He said they used to get the feed via direct feed.  Who is to say is hasn't changed since the storm?  

It must have been more than a couple months ago, as it has been longer since the digital transition.  TMJ would not have been completly off air for a couple days in that time frame.

[John L]

The employee is a friend of mine.  I believe him.

He said they used to get the feed via direct feed.  Who is to say is hasn't changed since the storm?  

It must have been more than a couple months ago, as it has been longer since the digital transition.  TMJ would not have been completly off air for a couple days in that time frame.

That depends on exactly what  the employee does there. Because the way or how ch. 4 is sent out or receive is really no concern or important issue to most employees at the station. Its only the concerns of the engineering and management staff regarding how ch. 4 signals are sent out.

No doubt ch. 4 feeds its signal to TWC via Fiber OPtic. Why would they change it back to receiving ch. 4 OTA?    The last thing you want is transmitter failure that would put ch. 4 out entirely as well as cable and satellite.  Should someone near the station accidently cut into the Fiber....the transmitter keeps going and TWC could temporarily switch to OTA until the Fiber Optic cable is fixed.

No down time is acceptable. WTMJ-TV MUST be all means provide 24/7 of continouis broadcasting. They are not allowed to sign off or stop broadcasting even between 12Mid and 5 AM.

-John L.

[WITI6fan]

No doubt ch. 4 feeds its signal to TWC via Fiber OPtic. Why would they change it back to receiving ch. 4 OTA?    The last thing you want is transmitter failure that would put ch. 4 out entirely as well as cable and satellite.  Should someone near the station accidently cut into the Fiber....the transmitter keeps going and TWC could temporarily switch to OTA until the Fiber Optic cable is fixed.

No down time is acceptable. WTMJ-TV MUST be all means provide 24/7 of continouis broadcasting. They are not allowed to sign off or stop broadcasting even between 12Mid and 5 AM.

-John L.

Plus, I would assume that ever since the storm mentioned earlier, WTMJ is probably building redundancy into their systems. It was probably the biggest storm of the summer and they couldn't even put up their beloved weather ticker because Master Control and half the building lost power when the lightning struck the tower.

They've probably paid to have the Fiber link restored, and probably have had microwave links to TWC installed on every other tower in the farm. :p

[John L]

They've probably paid to have the Fiber link restored, and probably have had microwave links to TWC installed on every other tower in the farm. :p

I find it hard to believe they would discontinue direct Fiber Optic Cable to TWC. But I suppose if WTMJ as well as WITI and WISN and probably WDJT have to pay and maintain that line.  But with the economy is bad as it has been, I suppose they would have to cut the cable and depend on TWC to receive the major network stations off the air.   This is terrible if thats the case.

-John L.

[Rick_EE]

No doubt ch. 4 feeds its signal to TWC via Fiber OPtic.
-John L.

The question here was directed at GM's and engineers.  I tried to help by quoting someone in the technical side of the business.  Hopefully someone with direct knowledge can answer and end speculation.  All I can say is what I was told, anything else is just guessing.

My source did also say that the links are paid for by TWC and the satellite providers, not the stations.

[ArgMeMatey]

This is the kind of question that Tim Cuprisin would have had answered in about five minutes.

[John L]

The question here was directed at GM's and engineers.  I tried to help by quoting someone in the technical side of the business.  Hopefully someone with direct knowledge can answer and end speculation.  All I can say is what I was told, anything else is just guessing.

My source did also say that the links are paid for by TWC and the satellite providers, not the stations.

You could be right.  If TWC and satellite providers are paying for the link then it must have been their decision, not the TV stations.  So if WTMJ-TV shuts down their DTV transmitter for maintenance during the wee hours of the morning, it will also mean losing WTMJ on cable and satellite.

-John L.

[wxndave]

Some stations in the Market feed TWC via fiber.  That is usually an agreement between TWC and the station on cost.  TWC owns the fiber that is installed at a station.  So no monthly cost other than the orginial instalation.  

Direct and Dish network orginally had fiber connections from the 4 major networks stations about 10 years ago.  That was leased fiber and was costing them a bundle across the country.   They now have a contract with Sprint to provide a receive site in each market.  Then they just fiber that one site back to the uplink site.  

Just so you know that TWC does not want large bandwidth from a station.  Infact they woulkd like less if possible.  They run a process called grooming, on all of the digital channels.

[techboy]

I am a former ( retired ) engineer at WTMJ.  I checked with the Engineering department, and TWC still gets their WTMJ TV fead via a fiber optic cable.  This assures that WTMJ can maintain service to the majority of viewers in the area even if there is a transmitter failure; just good business policy.

[Rick_EE]

I am a former ( retired ) engineer at WTMJ.  I checked with the Engineering department, and TWC still gets their WTMJ TV fead via a fiber optic cable.  This assures that WTMJ can maintain service to the majority of viewers in the area even if there is a transmitter failure; just good business policy.

I will have to yell at my friend.  I stood up for him.

Techboy- any chance you can investigate if the feed is a normal compression or the OTA compression?

[techboy]

TWC uses 64 bit QAM ( Quadature Amplitude modulation ) on their system.  So, you can't just compare TWC bit rate to OTA which is 8 bit Vistigial Sideband amplitude modulation.  Old analog OTA TV was also VSB modulation.  It's because you need a carrier to amplitude modulate and to save some bandwidth, the lower sideband ( vistigial part ) was limited to 1.25 Mhz.  The upper sideband was then 4.75 Mhz to complete the entire 6 MHz channel width.   So you ended up with about 4.2 Mhz for the video.  At about 80 lines of horizontal resolution per Mhz, analog TV maxed out at around 320 lines (square picture).  Getting digital TV to fit into the same 6 Mhz channel limits the bit rate to about 19 Mbps.  If only one video signal is encoded, it uses about 17.4 mbps for the video and the remainder is audio and various other info ( captions, program guide, etc ).  Perfect 1080i requires the entire 17.4 mbps.  Check ch 18 OTA, they use only one video channel and seem to have the best picture in the area.  But if you add more subchannels, then you need to divide up the bits over more signals, thus reducing the quality of each.  WTMJ OTA is only using 12.5 Mbps for their main video; not enough for good 1080i.  The remaining 5 mbps is going to the subchannels.  The HD video from TMJ which goes to TWC ( fiber optic ) is not compressed by WTMJ; compresion is done by TWC to meet the bandwidth requirements of the cable system.   I don't have TWC, so I can't compare picture quality myself.