Here's one station in Georgia that has 10 480i stations and 10 radio stations.
http://www.wanntv.com/
Obviously they must be using some type of compression or packet sharing techniques. With no psip/epg info as far as I can tell.

There is also a similar broadcaster in LA supporting 12 480i channels plus a few radio stations.

KAXT-CD is the LA station with 12 channels.

KAXT-CD is using Statistical multiplexing: [or Statistical time division multiplexing]
http://en.wikipedia.org/wiki/Statistical_multiplexing

WANN in Georgia is likely using the same techniques.

I don't understand how they applied this method to work OTA?
http://searchnetworking.techtarget.com/definition/STDM

From that article:
The main statistics used in STDM are: each input device's peak data rates (in kbps, or kilobytes per second), and each device's duty factors (which is the percentage of time the device typically spends either transmitting or receiving data).

In this case, data rate for each subchannel is continually analyzed and adjusted to minimize artifacts. Of course, priority can be assigned in order to keep quality for one at the expense of others.

Technically, stations are not sharing frequencies. Station A multiplexes station B's data to its stream and sends it out. There are several reasons why this happens in US markets.

First, there are markets, especially small ones, where there are not enough transmitters for all the networks. In the analog days stations would have secondary affiliations, and the programming from the secondary network would be shown at a different time. Now, a station can put their secondary network on a subchannel.

Second, co-owned stations sometimes back each other up with SD subchannels. This happened in LA and occurs in other markets, especially where one of the two stations doesn't quite cover the whole market.

^^^there is also a third reason (though this is similar to your second one):

Third, better coverage for a LPTV/Class A station. An example of this is WWNY (CBS) and WNYF (FOX) in Watertown, NY are both owned by United Communications Corporation. WNYF is a Class A station but not only do they broadcast in HD on their primary channel, but also broadcast in SD as a sub-channel on WWNY's full power transmitter to get better coverage. Interestingly WNYF has a repeater in Massena - South Colton that only broadcasts in SD but also has WWNY in HD on a sub-channel.

That is in small markets. In most markets in the US and Canada, the individual stations have indivudual transmitter facilities, at most sharing an antenna.
They major network commercial stations like that, because that gives them the perception of or an actual competitive advantage over other stations in the market, with transmitter loation HAAT, frequency, power, and antenna pattern.

You are asking more stations to use the same actual transmitters, which commercial stations might not want to do, which could eliminate that advantage.

Spotted this in the monthly Vermont Association of Broadcasters
The .pdf is here

http://www.vab.org/vabfebruary2012.pdf


It says that the FCC wants to clear out channels 31-51?
Perhaps I read it wrong. If true, I would think that would be a major problem for OTA.

Yes, the FCC is talking about doing that, though nothing is written in stone and the timeline isn't known. Most of the discussion in this thread for the past 6 months has been around this.

Here is something a little more up to date concerning the auctioning off of more TV spectrum

http://blog.broadcastengineering.com/blog-opinions/2012/02/17/congress-paves-way-for-broadcast-spectrum-auctions/

In Variety:
TV cord-cutting on the rise http://www.variety.com/article/VR1118050431.html?cmpid=RSS|News|TVNews

Blackburst, go back a few posts and read the opinion piece I linked to. Yes, the legislation is almost in place. Two major points to remember:

1) This is still a voluntary parocess for broadcasters. To be able to reclaim any reasonable amount of spectrum will require more than one or two stations per market in the northeast to participate. I do not see that happening.

2) DTV assignments within 200 miles or so of the Canadian border are negotiated and codified in agreements/letters of understanding between our two countries. This is a MAJOR impediment to redoing assignments in most of the northeast US to support auctions.

If wireless operators ever need more spectrum, it will be in urban areas where DTV is most heavily used. If this was all about broadband for rural areas, there's already plenty of spectrum for that.

I heard today that the americans are looking at chipping away at the spectrum again into the uhf below 700 mhz, I think that if the wireless companies get there way that it will be the end of over the air. :o

That's been the focus of this thread lately. I recommend going back a few pages and reviewing the discussion to catch up.

^^^ In fairness to Ndnile, his post was moved here from another off-topic thread.

Here (http://www.tvnewscheck.com/article/2012/02/27/57705/heres-whats-next-for-the-spectrum-auction) is an interview with a communications attorney that summarizes how the spectrum auction will (or won't) work based on the legislation just passed. Some things to note:

1) Canadian and Mexican cooperation will be needed. The lawyer predicts that some Canadian stations would have to change frequency to make this all work.

2) upwards of 10 stations each in the New York, Baltimore/Washington, and Los Angeles markets, plus participation of border area stations will be needed to make the auction work. Personally, I don't see 10 stations from my area wanting to sell.

If this plays out it will mean the following:
The death of OTA and subsequent rise of further cable TV subscription costs. If it costs approx $70/month now, imagine how much it'll cost after OTA is gone. This could potentially kill off the TV altogether.

The mobile networks don't really need any more spectrum, these are just power and money games. If anything, the VHF spectrum should be given to them. The rest should be stopped.

VHF-Hi is very important in mountainous regions, so please let's hope they don't touch it

In the mountains north of Montreal, channels 7, 8, 9 ,10, 11, 12, 13 are coming strong and clear depending were you are, at the contrary of UHF channels

Whoa! @alien0 and @mille, you need to read the article I linked to. The message is: the sky will not fall! The National Association of Broadcasters and others were able to have certain protections included in the legislation that will probably derail any auction. Some of those are:

1) NO shifting stations to a lower band in any repacking scheme! UHFs must stay in that band and hi-VHF stations must stay in that band.

2) only ONE auction will be allowed. The FCC cannot keep coming back for more.

The required international cooperation I mentioned before will certainly delay any proposed auction.

Don't worry!

Marketwatch (Wall Street Journal) article from March 6 - TV antenna boom a bad omen for Charter

http://www.marketwatch.com/story/tv-antenna-boom-bad-omen-for-charter-2012-03-06

Broadband With Broadcast-Only TV Households Jumped 14%

http://www.multichannel.com/article/484038-Cable_TV_Subs_Fell_5_In_2011_Nielsen.php