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From the Virtual Press Room:


April 8, 2002 Las Vegas, NV -- MSTV (the Association for Maximum Service Television) presented results from MSTV-conducted field testing of the LINX ATSC-compliant receiver, in a presentation at the NAB (National Association of Broadcasters) Convention. The testing substantiates the superior performance of the LINX receiver in heavy multipath environments.


The field test was conducted in three eastern U S cities; Washington, D.C., Baltimore and Philadelphia, during March. In all, 34 test sites were used, each with multiple receivable DTV channels. In excess of 250 reception tests were thus performed. While most of the testing was done outdoors, some indoor testing was included as well. Sites were selected to provide challenging multipath, a situation that often occurs in core urban areas where buildings block the line-of-sight to the transmitter, and reception must depend on multiple reflections of the desired signal off the buildings and terrain. In such a case, there is no single dominant signal, and the amplitudes of the reflections can vary over short time periods due to phenomena such as building sway.


On average, the LINX receiver was successful in receiving digital TV signals 80% of the time. By comparison, a reference receiver also included in the testing received successfully 40% of the time. That reference receiver was used in field testing of proposed ATSC receiver enhancements conducted within the last half year, also by MSTV, and was deemed to be the best available receiver for that testing. A second reference receiver was also tested, the same reference receiver used in earlier field testing of the LINX receiver in Chicago. That receiver was successful 32% of the time.


Victor Tawil, MSTV senior vice president, responsible for the testing, said, "LINX asked for difficult sites, and that is what they got. Those were not your average sites. Under such difficult circumstances, the LINX receiver generally performed very well."


Rich Citta, LINX' chief scientist said, "The LINX receiver has undergone other, earlier field testing, and we knew our performance. But, we needed a respected third party to verify that with their own set of tests. We appreciate MSTV's interest and offer to run the tests, and are very pleased that the results confirm our performance. At this point our business folks are cranking up the steam on commercialization. We want to get these benefits out to consumers. I'm heading back to the lab … we've got more good DTV reception stuff in our pipeline."


The testing was conducted using a van provided by Wallace & Associates. Outdoor measurements were taken at five feet above ground level, using a simple dipole antenna, tuned for Channel 34. The antenna was connected to a preamplifier, and then through a one hundred foot cable to the van, which contained the receivers and test equipment.


In Washington, D.C., the testing was conducted in the Rosslyn area of Arlington, VA, where there are a number of high rise buildings. Measurements were taken at 13 sites, with twelve DTV channels measured at each. The LINX receiver success rate was 82%, and with the lead reference receiver at 53%. In Baltimore, the measurements were taken at 9 sites in the downtown area, with 4 channels being measured. The LINX receiver success rate was 88%, with the reference receiver at 37%. In Philadelphia, there were 12 sites, each with 6 channels. The LINX receiver achieved 74%, with the reference receiver at 25%.
 

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And, unfortunately, people live indoors, not outdoors. There is all sorts of secondary multipath indoors and it would've been fascinating -- for the multiplicity of apartment dwellers who might use indoor antennas -- to see how this thing performs indoors.


A lot of people can eliminate outdoor multipath today with a directional antenna. Not everyone, for sure...


Still, it's good that someone is doing something positive to make OTA tuning better. We satellite subscribers need long-term solutions to receiving OTA networks because our providers will be unable to do much for us this decade.
 

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Quote:
Originally posted by Ken H
In Washington, D.C., the testing was conducted in the area of Arlington, VA, where there are a number of high rise buildings.
I'd love to see further details of that test. I have customers in the Rosslyn area of Arlington, VA, and it is a multipath nightmare. I installed a master antenna DTV headend on a twenty story building there and still had a battle with multipath, or, in the case of channel 43 from Manassas, "non-path", as there are too many comparable height buildings in the Ballston section of Arlington on the transmission path about two miles to the west to allow me a clean shot at that transmitting tower.

 

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I was at the live test in Chicago in the Winter and they did tests in the Tribune Tower indoors and it performed very very well. The reference receiver could get only 1 or two stations while the Linx got them all.


The delays are what's killing them, though. The big names are going to come up with a solution to this before Linx does, I think.
 

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Who cares who comes up with a solution first? What we are learning is that our "horrible" modulation scheme can fly far and wide through the air and that it's one bugaboo -- multipath -- can be dealt with using modern electronics.


Now, if someone can just help Mike in the meantime. :)


Mark
 

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I telephoned MSTV and the receptionist said that the web site I visited is the current one but that they just haven't updated it recently. It listed an October 2001 conference as an upcoming event. I also told her of my involvement in the industry (DTV master antenna system design and installation) but she seemed at a loss as to why I'd want to establish a relationship with MSTV, so she connected me to someone's voice mail and I left a message saying that if they provided any services that might be of use to me or thought that anything that my company did would be of use to them, to call me back, but I haven't yet heard from them.


This seems like what they used to say about Windows NT: If you need it, then you already know what it does, so there is no point in answering general queries about it. When I scanned a few links that came up in a search, the topics being discussed seemed to be matters for which FCC decisions were being contemplated, so maybe they are a technical lobbying or consulting firm. In particular, several of the links involved the 8VSB/CODFM controversy.


One thing to keep in mind when evaluating DTV reception success rates is that the reception success rate of analog in those same situations is nearly 100%, since we can watch and tolerate the content of a blurry or ghosty picture. When a tuner is 80+% successful in a certain market, what does that mean? Does it mean that five of six local stations were perfect and one could not be received at all? Does it mean that typically, a person in that market be able to watch local broadcast TV via set top antenna on just five of his six main networks? Who would accept that? And would one have to buy a $500 tuner to find out if his reception is acceptable?


Dealing with a consumer product whose signal has an avalanche failure characteristic is going to be a nightmare for hardware dealers. I stopped selling and servicing the so-called "free-to-air" digital, MPEG2 satellite receivers in part because I couldn't provide definitive explanations regarding intermittent performance failures of those products that were occasionally reported. With analog multipath, as least you can see the faint ghost. With digital multipath, you can't see or measure the multipath until it crosses the threshold at which it makes the reception wholly unacceptable. For the size of the profit I was making on MPEG2 satellite installation, it just wasn't worth the occasional hassle from dissatisfied customers. I installed a Sky Angel DTV system for a residential customer last month (I just wanted to see what they were furnishing for hardware), and the customer called me back twice, saying he was sure that the dish was loose because the reception was coming and going, so I came out and found that everything was perfect. When I asked him if it might have been raining when he experienced those problems, he said yes. I didn't charge him for the return call because he seemed to be of modest means, but if I have too may of those calls, I'll become of modest means.


I generally turn down requests for off-air attic installations for DTV residential antennas as well, and if a prospective caller for a roof-mounted antenna starts giving me the third degree regarding my warranty of customer satisfaction, or if he indicates that he has been visiting internet forums and wants to ague about the selection of the antenna that I am making, I also decline the job, again, because the profit is too small to have any tail service or hand-holding responsibilities. I can make a little money installing residential DTV antennas, but I have to pick and choose from among my prospective customers and am in a position to do so, however the person working in a consumer electronics store who is trying to sell a $3,000+ TV and who is asked by the customer if he should be able to get good reception where he lives using a set top antennas is under a lot more pressure to make the sale than I am. For those sellers anything less than a 100% success rate risks customer complaints and returned merchandise.
 
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