It seems like no thread is really applicable to this so I'm trying it here.

Everything I've read says the FCC expects broadcasters to provide equivalent coverage with their digital transmitters to their current analog transmitters. What does that mean in a world where digital is receive it or not and analog is everything from a perfect picture to a barely perceptible picture?

I know some people watch some pretty bad analog pictures. What level of analog PQ should be necessary in order for the digital transmission to be received? Let's leave out the complicating factor of multipath here.

I photographed 6 different analog stations ranging from a perfect picture to one so weak that it was on the edge of going to B&W.

http://images.aa6g.org/pq.jpg

The percent numbers are my estimates of percent picture quieting and won't necessarily conform to anyone else's. At what analog picture quality should the digital station be receivable?

I'm seeing a large variation here, from 25% to 90%. I suspect that many people who are watching less than perfect analog TV are going to be surprised with no picture at all when they switch to digital.

I know there are better ways to quantify this like with a spectrum analyzer but few people have access to that sort of equipment.

This might seem like a pointless exercise but there are a lot of DTV stations on the air right now that don't have duplicate coverage because they're not yet at full power, antennas are not in their final positions, they have directional antennas protecting analog stations in other areas, and most low power stations have no digital stations yet. I thought it might be useful to view these analog stations and get an idea if they will be receiveable after the transition.

This runs both ways though. I have 3 examples of analog stations that are not receivable because of co-channel interference but are receivable on their digital channels!

It seems like no thread is really applicable to this so I'm trying it here.

Everything I've read says the FCC expects broadcasters to provide equivalent coverage with their digital transmitters to their current analog transmitters. What does that mean in a world where digital is receive it or not and analog is everything from a perfect picture to a barely perceptible picture?

I know some people watch some pretty bad analog pictures. What level of analog PQ should be necessary in order for the digital transmission to be received? Let's leave out the complicating factor of multipath here.

I photographed 6 different analog stations ranging from a perfect picture to one so weak that it was on the edge of going to B&W.

http://images.aa6g.org/pq.jpg

Thiie percent numbers are my estimates of percent picture quieting and won't necessarily conform to anyone else's. At what analog picture quality should the digital station be receivable?

I'm seeing a large variation here, from 25% to 90%. I suspect that many people who are watching less than perfect analog TV are going to be surprised with no picture at all when they switch to digital.

I know there are better ways to quantify this like with a spectrum analyzer but few people have access to that sort of equipment.

This might seem like a pointless exercise but there are a lot of DTV stations on the air right now that don't have duplicate coverage because they're not yet at full power, antennas are not in their final positions, they have directional antennas protecting analog stations in other areas, and most low power stations have no digital stations yet. I thought it might be useful to view these analog stations and get an idea if they will be receiveable after the transition.

This runs both ways though. I have 3 examples of analog stations that are not receivable because of co-channel interference but are receivable on their digital channels!
i'm surprised you haven't been moved over to the non hdtv thread.

Just now I tested some of my more distant stations by rotating my antenna until the digital picture started to break up seriously and my STB's "signal strength" indicator dropped significantly. At that point the average analog PQ looked like it was near your "75%" picture, maybe a bit less.

Here in albuquerque, a few of my local stations either do not come in or extremely staticy when tuned in on my one rememaining analog tuner. Yet each of my 4 other Digital tvs lock on to every local digital station providing a perfectly clear picture.

I beleive the FCC considers equivalent coverage not based on how far someone can actually receive a signal but the theoretical coverage area the station is licensed for. Sometimes the analog signal can be received further away than this. Sometimes the digital signal may not even make it to an antenna due to other obstacles.

Have you tried http://www.antennaweb.org to see where to best point your antenna? Maybe look for a bigger antenna or a mast to raise it up higher.

Good luck either way.

In your photos, the only problem is a weak signal/snow. The ATSC standard was designed with this situation in mind and is pretty good at recovering weak snowy signals because all the noise is equal in amplitude, time diversified and thus evenly spread out. If snow is the only problem, the threshold of when the decoder will unable to lock on the signal is a a bit below the 50% picture.

Digital does not do nearly as well when dealing with external interference. Especially the kind found on the VHF band. Impulse type noise, such as electrical noise , is not time diversified and will corrupt too many bits at once. ATSC was not designed to cope with bursts of noise. If you take the 75% picture and add some hash noise from some power lines, or a computer switching power supply the error correction will be pretty close the limit. VHF HDTV stations are vulnerable to this, especially the low band ones.

The sweet spot for reliability is actually the UHF station with the 75% analog picture. It's strong enough to keep the digital signal quality in the decoder in the 80's, but weak enough that multipath is less likely to cause problems. When the analog signal is 90-100% multipath issues greatly increase.

The people who are going to suffer the most problems post 2009 are the ones who are currently experiencing signal ghosts, or RFI.

The sweet spot for reliability is actually the UHF station with the 75% analog picture. It's strong enough to keep the digital signal quality in the decoder in the 80's, but weak enough that multipath is less likely to cause problems. When the analog signal is 90-100% multipath issues greatly increase.

The people who are going to suffer the most problems post 2009 are the ones who are currently experiencing signal ghosts, or RFI.

Thanks for your insights. Electrical noise isn't mentioned a lot except for those suffering with low VHF digital stations. Electrical noise is much less on high VHF but it's not completely absent. Too bad they didn't just go all UHF where electrical noise is almost never a problem. It's also much easier to stack UHF antennas to combat multipath than it is on VHF.

50% to 75% as shown in my pictures seems to be a pretty reasonable range to receive the digital station. Anything below 50% is so poor I wouldn't want to watch it anyway. Let's hope the broadcasters actually meet that criteria.