OTA tuner sensitivity

Some TV's and converters have diagnostic displays that shows some details. When you disclose exact model numbers of the receivers and converters that you're testing, it might be possible to find the diagnostic page.

Baloney. My antique Sadelco 719B meter (the one with FOUR 9v batteries), still works. It indicates the signal strength of the OTA digital stuff just fine. It won't demodulate the audio, but the signal strength is still usable. What model Sadelco are you using?

Nope. That's because, like you, I'm using a tower mounted amplifier. With such an arrangement, the RX sensitivity is almost totally determined by the amplifier noise figure. You could compare a high quality receiver with a piece of junk, and they would be about the same sensitivity. Now, there are some things that will make a receiver worse, such as digital noise in the receiver front end, overload by adjacent channel stations, ability to deal with reflections, etc. Hard to tell from here.

I wouldn't mind one of those myself. I used to own one of those government subsidized converter boxes (Zenith DTT901), that had an on screen diagnostic page. All CECB certified converters are required to have an on screen signal strength meter. However, there's a catch. Most converters do not show signal strength. They show "signal quality" which is usually calculated from the BER (bit error rate) of the decoded DTV signal. This is somewhat related to signal strength, but can easily be trashed by adjacent channel junk, internal digital noise, reflections, etc.

Another possibility would be to purchase a laptop or PC based ATSC tuner, and use that as the receiver. With luck and diligence, you might be able to find some kind of open source diagnostic program that can be used as a tester. At a minimum, something that dumps PSIP data from the station.

There's plenty of test equipment available:

but most of them look rather lame.

Better: (in UK)

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

"which is usually calculated from the BER (bit error rate) of the decoded DTV signal."

Sweet. They are guaging the quality of the signal, for their particular product, chipset, whatever. This gets me wondering, for one, what if you ar einstalling an antenna without a rotor ? I happen to know a few places in this city where the reflections are so bad that you NEED cable. Just the lay of the land and a bunch of buildings. It didn't work with analog, even though there is plenty of signal strength. This is extremely bad folks, but I don't live there. At my house analog was quite good. I did get some DX out of the attic but because I needed multiple outlets, the amp just didn't do the out of town stations justice. It's really not worth big bucks, basic stripped cable is cheap enough.

But signal quality is a whole nother thing here. More processing power could mean being able to decode a signal that would be unusable to a lesser reciever. So how do we test this ? First of all there must be adequate signal strength. Then as far as I can figure feed a signal into an amp and then a splitter to two different recievers and find out which one corrects and/or recovers from the errors the best. Split AFTER the amp, you can screw with the signal level before the amp to put the recievers through their paces.

There was already contrived a ghost eliminator for NTSC, though I have never seen one I have read the specs on it and how it works, vertical interval stuff again..... I thought they should be able to do it off the old usual VITS but.......

So of course this device uses multiple time delays and nulls out components based upon what was detected in the reference, yada yada yada. This is all digital of course, well now WE ARE TALKING DIGITAL so that should already be built I would think. The ability to correct for multipath. Sorta lika a WAAY adaptable COMB filter.

So it is probably in that area in these recievers that determines the optimum performance. Also some people need different parameters than others. In this case, deep fringe, well it may be easier to deal with if you get enough aerial, altitude and amplification, the three As. But in an urban environment, more processing power would help more than a kickass front end.

I think I could easily devise a setup to test these things, but I wonder if it's worth it. Who would pay me ? Concievably some magazine or something, one of the ones that review video equipment. OK that makes sense except for one thing. People who read magazines to figure out which TV to buy are not using convertor boxes. They got HD sets on dishes or cable or internet TV or something. The only antenna in their house may be on the router.

J

I didn't figger out from your post where you're located. Makes a difference. Here in the good ole USA, OTA HDTV sucks. Encoding was picked by lobbyists, not engineers.

I'm only 10 miles from the transmitters, but there's a hill in the middle and a two-story metal pole building in my neighbor's yard. It's multipath city here. Ability to decode a channel also depends on the season and how many leaves the intermediate trees have.

I have a combo VHF/UHF antenna on a rotor, but if you wanna record more than one thing at a time, you can't be turning the antenna.

The Zenith DTT901's work pretty well, unless it's raining hard, but the output isn't HD.

I have several older cable boxes that work on some channels. It's particularly annoying on some boxes that there's no way to add channels. If you need a different antenna direction to detect a channel, you can't find all the channels with the auto scan.

The ATSC tuner card in the PC works the worst. And it's not signal strength. I put a variable attenuator in the antenna line and tweak it per channel for fewest dropouts.

Before the big switch, when most of the ATSC channels were on UHF, signals were much better. After the switch, when they went back to VHF ATSC, it got much worse.

I put the signal on a spectrum analyzer. There's no correlation between signal strength and stability of the picture. The "Bart's head" display is supposed to be flat on top. There is a correlation between the flatness of the top and the stability of the picture.

I have a friend in the industry. He won't disclose details, but he claims that the math to de-multipath the signal exists. But it takes more computing horsepower than you can get into a cheapo set top box with current technology.

I'm unwilling to spend much money on this. The whole idea of free TV is that it be FREE. I'd much rather have NTSC quailty than "no signal" scrolling across the screen of what I thought I'd taped.

Nice idea. Basically, it's a 600MHz waveguide, with a yagi inside. Something like a horn antenna. It should work for frequencies about

600MHz, but won't do much for the lower UHF channels. The main thing that it does is block the side lobes, which are where the reflections are probably coming from.

The author thinks the multipath is coming from the buildings in the distance. I disagree as my guess(tm) of the increased path length is insufficient to cause cancellation (frequency selective fading). The wire screen horn won't do much for eliminating reflections from something that's almost straight ahead anyway.

What the wire screen horn does do is block reflections from the side and most important, from the back. However, my guess(tm) is that the multipath is coming from BEHIND the antenna, not in front. It's really easy to test where it's coming from if you get near the antenna. Take a sheet of anti-static IC foam (mostly carbon), or a wet towel, and move it around the antenna. When the ghosts disappear, that's the direction of the reflection. The idea behind the foam and wet towel is that you want an absorber, rather than a reflector. That would also apply to the horn construction. Instead of wire screen (reflector), it really should be made of something that absorbs RF.

It will work the same with solid metal. You could use aluminum foil on box cardboard as long as all the edges are connected. If you're lazy, shove the antenna into a 55 gallon drum.

Detuning will probably be severe. I can do an NEC2 model to see how bad, but I couldn't find an antenna model close enough to clone:

I'm at home with a cold or flu. Thinking hurts. Another time.

What about the feed line? If the 75MHz antenna is horizontally polarized, and you run the coax down the boom, and then down the fiberglass mast, you may have problems. You'll have fewer problems if the antenna has a balun to keep the coax from radiating. The only way you can keep the feed line out of the pattern with a yagi is to cantilever mount the antenna by the boom behind the reflector, and run the coax down the boom.

Shield.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

On Jan 1, 3:07=A0pm, mike wrote: >

You really have DTV on 2, 6 and 8? I checked this list and found only

6 channel 2 DTVs in the entire country.

The first DVR PC I used was an AMD Sempron on a cheap ECS mobo wit 512 megs RAM and an ATI 9200 video card. The ATI software needed 20-40% CPU and would stutter if surfing the web while it was recording. The later Gigabyte 780 series boards with AMD Phenom II quad core processors never stutter and can watch an HD recording while recording another HD AND play out another HD stream across the LAN to another PC. 2 machines have ATI HDTV Wonders ( I have 2 more machines off line that have Wonders also). All machines run Win XP Pro SP3. The ATI software is MMC 9.14 which has quirks but rarely screws up. The 3rd machine has a Hauppauge 1250 tuner. None of the machines stutters but the Hauppauge can handle dynamic ghosting better than the ATIs back when I had antenna issues a few years back. The Hauppauge machine uses WinTV v6 as the recording software and it too rarely screws up. Commercials are removed with VideoReDo. All the machines are shut down cold every night. The monitors and disk drives are never shut down during the day. All have 1.5T drives and secondary drives as well, 1

500GB, 1 1T and 1 2T for a total of 8T spinning between 3 machines with another 8T of USB drives.

We live in zip 90274 about 35 miles from Mt. Wilson and run a Winegard SquareShooter on the roof for the UHF channels. The VHF (7, 9, 11, 13) are picked up with a Winegard 7082 (20 yrs old but only 1 year outdoors) in the rafters of the garage about 8 ft lower than the roof antenna. They're combined with a UHF / VHF splitter running backwards as a diplexer (combiner) and no preamps with the feed split 4 ways. Channel 7 reports 66% on the ATI tuners. All other channels are 80-90% The Hauppauge tuner reports S/N ratio. Ch 7 comes in at 25dB+ and the rest max out at 30dB. For DTV at least 15dB S/N is required.

For most areas of the country the Winegard HD7694 would be an excellent choice. Good gain and front/back ratio and directivity and not big BUT it's no good for ch2-6 (actual digital channels, NOT virtual channels) and FM.

If you need ch 2-6 and.or FM this will do well but its BIG. It's basically the specs of the 7694 but with low band VHF. The thing about these guys is that they get their engineering right and don't make outlandish claims. They just WORK.

Excessive signal strength can cause overload issues but it's also possible that the in line attenuator improves the termination of the line and reduces reflections (same as multipath) in the transmission line. The antenna itself and transmission line (connector installation) can cause this as well. After reading on other groups I switched to Snap n Seal connectors and outdoors under weather boots I use clear heat sink grease (GC 10-8101) on the cable end to keep oxygen out of the connector. I dissembled a connector 15 years old with that treatment and it looked new inside. Pay attention to the details and you won't have big issues.

Did you notice page 2 of the Georgia Tech antenna? It's even better than page 1. I've wondered if you could use a wire basket instead of a trash can to reduce wind loading.

G=B2