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It has only failed once in about four years.

Wasn't me who said that but our computer expert. He knows this stuff inside out.

So does ours. Some stations show the next 24hrs but not a whole week. Others simply state "8:30 am - DTV programming". Not a lot of information there.

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One thing you have to do with the Vizio is adjust the settings. At least the color. It's over-saturated but that's easy to correct. I didn't even have to get off the couch for that :-)

Actually that format puzzle is quite annoying. Especially during commercials they happily switch back and forth between them. When the newscaster returns it's still the old TV format, just digital. No wide screen out here except for movies (and only some of them).

Joerg,

2) what receiver are you using, Do you know what generation design it is?

4) Do you by chance have a spectrum anlyzer and can look at the RF signal?

Multipath is THE major problem with digital TV.

Mark

In Cameron Park, about 35 miles east of Sacramento, towards Lake Tahoe.

It's the latest version Vizio 37", VX37L.

A rather huge log-periodic on a mast.

It looks ugly. Lots of signal strength but lots of selective fading that already happens when a freighter lines up for final into Mather Field. Fedex, Lufthansa Cargo, UPS, you name it. It's a major hub by now, used to be a military base.

We have a clear shot through a narrow Hwy 50 gap but it is so small that echoes from that ridge already come back in.

When faced with UHF problems as you describe, when I lived in North Scottsdale, I rolled my own helical, because lots of "fading" (at least in AZ) was just wandering polarization from the heat.

...Jim Thompson

I think he would be far better off with a more directional solution

Good idea. And yes, I think much of the multipath comes back polarization-twisted.

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Well, t'is already the biggest honking ChannelMaster antenna there was. Not the cheap stuff.

Joerg hath wroth:

Bingo. Are you *SURE* it's really a log periodic antenna or some kludge that only looks like one? Duz it look like one of these?

I modeled a few of the Radio Shock TV antennas with 4NEC2 to see what they were doing. The results were awful. On some channels, it had more gain out the back of the antenna than in the forward direction. Impedance matching was awful and varied wildly across the frequency range. Side lobes were all over the place. There were nulls in the forward direction on some channels.

Under ideal conditions, a real log periodic has a forward gain of only

I live in the Santa Cruz mountains. Before I gave up and went with DirecTV satellite TV, I used a mast, rotator, and tangle of antennas on the roof. Multipath from the nearby mountains was a serious problem with Radio Shack antennas. Even the one station that was line of sight had reflection problems.

So, I started to play with antennas. My first solution was a simple bow tie antenna with a flat barbeque grill reflector. That worked very well for UHF, but was too small for the VHF channels. It's main advantage was that it was very broadband, few side lobes, and excellent f/b. However, it didn't have much gain (about 4dBi).

Looking for something better, I decided that single channel yagi antennas were the only way. The commerical versions are:

However, I built my own. I had 4 different dipoles, pointed at the 4 transmitter locations. Gain was about 10dBi for VHF and 12dBi for UHF, a substantial improvement over broadband antennas. Each antenna had a really ugly homemade Dual Gate MOS FET RF amplifier at roof level, with a combiner feeding the TV. I removed the rotator as it was un-necessary with one antenna per transmitter/channel. Fine aiming required a 20ft fiber glass pole to bang on the boom in one direction or other.

The results were a dramatic improvement in reception signal strength and quality. There were still a few ghosts visible but nothing as horrible as with previous antennas. I was happy for about a year, when a large fir tree branch managed to mangle 3 out of 4 antennas. As I was recovering from surgery at the time, and was in no condition to do anything major, I ordered DirecTV and gave up.

That's "frequency selective fading" and tends to be difficult to fix unless you have a very very very narrow front beamwidth with no side lobes and no ground bounce. If you have the possibility of reflections from behind, also good f/b ratio. If these are difficult, you might want to consider dual diversity antennas (about 10 wavelengths apart), with dual tuners and a diversity switch. If the signal level to one antenna falls due to frequency selective fading, the odds are good that the other antenna will still have a usable signal.

Nope. Politics is the major problem. If the FCC would have approved European COFDM modulation instead of crappy 8VSB, we would not have as many multipath problem.

The FCC has several chances to listen to sane technical comparisons, but elected to follow the path paved by the US patent owners.

That's going to be very difficult to reduce multipath if both the incident and reflected signals are coming from so close a direction. Diversity reception might be the only workable band-aid. However, in my limited experience with such multipath, that doesn't happen as much as one would think. The reflected path ghost delay is usually so small, that it's only visible as a slight smear to the right. The reflections that generate the really visible ghosts, usually come from the back, and sometimes from the sides. A good antenna pattern will eliminate those.

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Maybe you should try turning it then.

Perhaps it has so many damned element that you are contributing to your own perceived problem.

Mine worked fine from indoors set top, and I was over 40 miles East from the transmitters, and down in a valley from them.

Funny thing was, from there, I only needed to point in one direction to get all the stations. From just 12 miles both North and East from them, I had to point in several directions dependent on what direction whatever particular station was in from where I was. Now, I am 40 miles North of them at sea level, and still have several vectors needed. Most all are Southerly, however.

They are in San Diego. I was in Santee for years with no problem and great signal. In Clairemont (an SD suburb), and now in Oceanside, I have to move the antenna around a lot more. Perhaps what HD tuners need is true diversity, where there are like four tuners inside, and four antennas, and the signal is garnered from them all to compile a complete data stream. It sounds like overkill, but diversity really does work. That's what they use at all the NASCAR race tracks, and at Indy.

Diversity receivers.

On a sunny day (Sun, 25 Nov 2007 18:46:39 -0800) it happened Joerg wrote in :

Joerg, I have been thinking about your case, where you have one direct path and one airplane reflected path. With 2 path destructive interference can cause zero signal. Then I had this funny idea: Why not use a wider beam antenna then your log periodic? With some more refections the sum is not so likely to become zero... But this will only work with sufficient signal strenth,

I turned my antenne 90 degrees to vertical, it is a bow tie, it has a wide angle. I can now get some other stations, likely (but not 100% sure) one 120 miles away (40kW high tower), but some are now on the same frequency, so hard to say if I get the one or the other... There must be a station ID in the DTV tables, but I would have to look up the Etsi documents, and write the soft to grab it perhaps.

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I used corrugated fiberglass roofing rolled into an 8' long tube, then used 1/4" copper tubing as the helix ;-)

...Jim Thompson

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That stuff doesn't always last long out here. The repeated heat/freeze must take a toll. One day it goes phhhst ... crunch and just breaks open, fibers sticking out like fuzz. Seen it again during our dog walk yesterday.

Freq Selective fading is casued by multipath, they are two views of the the same thing.. one view in the time domain the other the freq domain. If you have deep nulls across the channel the two rays are almost equal in power. If you have one null then the delay is about

8VSB needs a good equalizer in the receiver to overcome multipath. COFDM is more naturally immue to multipath but is more suseptable to impulse noise. Each impulse wipes out all the carriers and a lot of symbols. With 8VSB, each impulse wipes out only a few symbols.

Mark

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Did that :-(

It certainly ain't perceived. Yesterday was the worst: Channel 13 news. Watched it on digital channel 13.1. Clouds rolled in, picture became blocky, audio cut out at times. Image got more blocky, then froze, audio gone as well. Switched back to 13 analog -> H-sync a wee bit tipsy but a clear image. The comb filter didn't get all reflections, could see about half a dozen weak ghosts. But the fact of the matter is we could watch the news on the analog channel while on their digital channel we could not.

So unfortunately I have to stand by what I suspected all along: DTV is not as reliable as analog. Not even close. The local politicians might want to stock up on anti-depressants come early 2009 ...

I know diversity well. We even have it at church for the wireless mikes. However, terrestrial broadcast is low on the pecking order because the majority is in the hands of the big cable and sat companies. So I doubt the industry will invest much there. Certainly not a 2nd tuner, probably not even a 2nd F-connection.

It does, just a whole lot bigger.

It is much sharper. I spend hours on the ladder turning it. You can completely lose a station into the noise at those 30-50 degrees.

Well, I don't wnat to go to that length ;-)

TV isn't too important and nowadays monitors have PC connectors. So eventually people might be able to cut it all loose and obtain their teevee from the web. Some day.

Well, I guess it is too late now. Whatever happens, when this leads to unpleasant consumer feedback in 2009 someone will dig into the matter of "who dunnit".

Out here there are echoes with very long delays. Tens of microseconds.

You can bet that the cable and satellite TV companies will use the cessation of over-the-air NTSC as part of advertising campaigns to get people to start paying them every month for the "privilege" of watching local TV.

I'm sorry to hear that even a new ATSC receiver isn't working very well for you, Joerg.

---Joel