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Linx corporation, who is developing technology for improved 8-VSB reception, is demoing their technology in Chicago today. If anyone is attending, please post your observations. Thanks.




Tribune Broadcasting and LINX Electronics invite you to:


Event: Chicago Core Field Test

Date: Thursday, December 12, 2002

Time: 11 a.m.

Location: Tribune Tower, 435 N. Michigan Avenue, Chicago


Tribune Broadcasting and LINX Electronics have been conducting field testing of the LINX DTV receiver in the Chicago area, with particular focus on downtown, a difficult urban canyon reception area. You will witness measurements being taken at a test site within the Tribune Tower. The Tribune Tower is located between the Sears and Hancock Towers, and the test site is chosen to not have a line-of-sight to the transmitters. The LINX receiver and a 2nd generation reference receiver will be compared in this high multipath environment. There are ten off-air channels available, and a variety of antennas.


The event will start with a presentation of overall results from the Chicago testing. The field test will immediately follow, and lunch will be available. Depending on how many people attend, smaller groups may be formed to go to the field test, which will be in a different room.


Please RSVP if you plan to attend, by replying to "[email protected]". We will provide additional info to attendees later, e.g., what to do when you arrive at the building.


For those who come to Chicago the night before, there are many hotels nearby. Two close hotels, found on Expedia:


Hotel 71, at Wacker Drive and Michigan Avenue (the closest 4 star hotel, one block away; $130 per night)


Wyndham Downtown Chicago, Ontario and Clair (less expensive 4 star, two blocks away; $100)


Bob

___________________________________________

Robert M. Rast

LINX Electronics, Inc.

Voice: (847) 776-2315, ext. 236

Cell: (847) 927-8006
[email protected]
 

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Great, they got back to me right away so I'll be attending. I'll let you all know as soon as I get back how it went. I do have high hopes for this! I live in one of the worst canyon areas you can imagine, and in fact very close to the Tribune tower. Can't wait.
 

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I have been really interested in seeing how the Casper chip performs. peter0302, I can't wait for your comments.


Rick
 

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Alright, here goes:


One word: excellent.


The event consisted of two parts: the first was a presentation of their latest test results from several sites all over Chicago - one of which was a block away from my apartment. On all the tests, the Linx Receiver got 8, 9, or 10 / 10 channels with almost no dropouts, while the reference receiver (a generic 2nd generation commercial receiver which they did not want to give details on because that company would probably be buying their chips), usually got 1 or 2 stations at most. So right away that was extremely impressive.


But the even better demonstration was the live test on the 11th floor of the Tribune building. From the windows you could see nothing but other buildings - no line of site to the Sears or the Hancock. The spectrum analyzer readings all showed terrible multipath from all the signals, and in some cases extremely weak signals. In each case, the Linx Receiver could receive each station, most with no droupouts at all, whereas the reference could only receive I think three stations. The Linx could even receive Fox (31) which no one, including them, thought it would be able to do because of the adjacent channel interference.


I'm afraid a lot of the engineering discussion escaped me, but I did understand enough to know that in big cities there's no doubt that these receivers will consistently be able to pick up most channels, probably 70% to in many cases 100% of the channels, and have reliability somewhere in the 90%'s.


Some of the live testing also involved moving the antennas (which were a simple dipole, and a Radioshack Double Bowtie) around to see what happened. While you could not get a signal at every single angle (even on the Linx), at most angles you could, and when the antenna was pointed toward the window the receiver got all 10 stations relatively flawlessly.


If anyone has any other specific questions please post.
 

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peter0302,


Thanks for the report. This is quite a leap forward for the reception of ATSC. I'm surprised this thread isn't generating more interest. I think this can really help the non technical people who just want to put up an antenna and be able to receive all their stations.


As for me I have a 1st gen HDTV receiver along with two HiPix cards for timeshifting. I just recently got Comcast HD service. Now if they incorporate this chip into a HD card I'm game.


Thanks again for your report.

Rick
 

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"I think this can really help the non technical people who just want to put up an antenna and be able to receive all their stations. "


Exactly - that's what hit home with me about the whole thing. He placed the antenna on the table and once placed he didn't move it at all - they took what they could get. And in each case he got all the channels with almost no dropouts. This is great news for those of us who hate fooling around with positioning antennas just to see a different channel. You can just find a good spot and just mount it and that's the end of it.


lvthunder,

That might be tricky, because I don't know whether mountain peaks reflect TV signals. That's what it all depends on. This thing takes all the reflections and somehow combines them all together - but if there's no reflections obviously it won't work.


It's clearly been made with indoor city use in mind (which is a huge % of the US population of course, and which will soon be forced to switch to digital).


Peter
 

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Thanks for the report!


This is fantastic! If this is as good as it sounds, OTA has an extremely bright future.


I really wonder if DTV OTA becomes easy and inexpensive, how much cable TV will lose out. So many people I know get cable just to get decent TV reception either in places where they can't put up an antenna, or simply don't want to bother.


The only downside seems to be that this technology is probably 18-24 months off, since the chips are sampling until fall of next year, according to their website.


Did they provide any ideas as to when these might be incorported into commercial products???
 

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Comparing to a "2nd" generation set is silly. They need to

compare to the current Samsung and Zenith sets.


Their published claims are good. Reception of the Brazil C, D, and

especially E ensembles is impressive. Note that DVB-T (COFDM .....

there, I said it .....) was unable to get E in Brazil (but ISDB, also

COFDM, did). The only claim, before these people, of reception of ATSC

on any of Brazil C, D, or E, even in simulation,

was my own design in simulation. Brazil E is TWO 0 dB ghosts ... three signals of identical strength, two of which are reflections) and is tough.


The published specs of the Linx are good but not stellar. While they are

able to get Brazil C, D, and E, the dynamic performance for them is

pathetic (i.e. if one echo changes phase faster than about once per

second , they fail.) This means that if one echo is from an airplane,

it fails. The only design to do better is mine, in simulation, which does them

at up to 15 Hz.


However, my design does not like either a single 0 dB echo or

Brazil E in the presence of impulse noise. The best test of whether

the Linx design is the cat's meow or merely another pretender is to see if it still works with Brazil C, D, or E in the presence of even single isolated

noise impulses at +3 dB (i.e. stronger than signal.)


Doug McDonald
 

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Unfortunately no firm dates were given.


Doug, a bunch of people did seem skeptical about comparing the Linx to 2nd generation receivers and they did take some heat on that from the audience. But the thing is, I tried the Samsung T151 in my apartment and it could only get 2 channels - NBC and ABC, and never at the same time. And the Linx got near perfect reception on every channel in an environment not unlike my own, and on their field tests, one of which was conducted not one block away from me! They also positioned their antennas for the ideal position for the reference receiver, (not their own) and then measured their own receiver's performance off of that position.


In short I am sure someone will always be able to find fault with this technology but there's absolutely no doubt that this is the best one yet and will make DTV reception a reality for 10's of millions of city dwellers who've as of yet been left in the cold.
 

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Quote:
Originally posted by peter0302
This thing takes all the reflections and somehow combines them all together - but if there's no reflections obviously it won't work.
I suspect what it actually does is to lock onto a single, strong signal path and reject everything else on that frequency. Much easier to do with digital than with analog. Anyhow, you're right that it won't help in situations where the problem is simply weak or no signal.
 

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I believe that the chip is specifically marketed as one that accepts and processes the multipathed ghosts, as opposed to existing technology that tries to do exactly what you describe - lock onto one and reject the rest. Hence, it's called "Casper" as being friendly to ghosts. :)
 

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:D
 

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Quote:
Originally posted by peter0302
I believe that the chip is specifically marketed as one that accepts and processes the multipathed ghosts, as opposed to existing technology that tries to do exactly what you describe - lock onto one and reject the rest. Hence, it's called "Casper" as being friendly to ghosts. :)
That's marketing hype.


**ALL** sets do the same thing .... they all have some sort of "transveral filter" (or its equivalent using Discrete Fourier Transforms) that "processes the multipathed ghosts". What this filter does is delay the signal by a large number of times, and for each time it adds or subtracts a little bit from the

original, trying to get rid of the ghost. But this introduces a ghost

of the ghost, so they have to do it again to get rid of that.



The trick is how to decide exactly what to do at each time, whether to use

the incoming signal as is, or after it gets converted to a digital signal, and how fast to change the filter coefficients.


It's very very tricky. There is no mathematical theory of this, because

it is hybrid analog and digital. There **IS** a theory for the

all analog case but it's not very useful in practice.


Doug McDonald
 

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From Linx' web site:


"LX1080TX is a 'Ghost-Friendly' ATSC standard compliant receiver. In contrast to the existing solutions trying to remove multiple ghosts, **LX1080TX combines the signal energies in complex multiple ghosts** to deliver near optimal DTV reception performance. LX1080TX is a receiver oriented solution."
 

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Sounds like it could be quite a leap over the existing tuners...


But, their www site also says: "Samples of LX1080TX will be available by the 4th quarter of 2003". If they are anything like chip vendors in other markets, that estimate could easily slide into Q1'04 or Q2'04. Then, how long until we would actually see products based on this chip?
 

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This kind of sounds like a product I'm familiar in the wireless ISP field. Redline communications makes a point to point radio in the 5.8ghz band that uses multipath to it's benifit for non line of sight (NLOS) applications. But, I think that if there is a big mountain between each link, and nothing elsewhere to reflect off of, you aren't going to have a signal.

Bob C
 
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