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Can someone shed some light on why it isn't possible for a QAM to 8VSB signal converter to be built?


There are lots of us who cannot receive terrestrial HD broadcasts (yes, I've tried) but who _can_ get unencrypted HD local channels from our cable companies for a low price. Most of the HD DirecTV decoders (including my samsung) can only read 8VSB-encoded channels.


Is there any hope for piping in the QAM cable feeds into an 8VSB-only box? Is it more than just a signal encoding conversion?
 

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I think the word is "economically feasible".


Hong.
 

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Quote:
Originally posted by sdossick

Can someone shed some light on why it isn't possible for a QAM to 8VSB signal converter to be built?
It's possible. However, although the parts cost is low, development cost is high, and consumer demand is low, resulting in a high price per unit. A QAM-to-8VSB converter would probably cost more than an QAM-compatible HDTV receiver.
 

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R. L. Drake also makes equipment that can do this for less than Scientific Atlanta charges. I priced some of it last year. I only remember the rough order of magnitude of the component pricing (too high for my application) which was to receive and demodulate broadcast 8VSB on one UHF channel and convert it to another for alternate channel reinsertion into the broadcast 8VSB band where I was concerned about otherwise having an adjacent channel interference problem. I think that a QAM demodulator, an 8VSM modulator, the supporting rack cage and power supply would run you somewhere around $1,000 to $1,500.


R. L. Drake and Blonder-Tongue both make devices that take the 30 MZ transponder-width QPSK DirecTV and DISH network transmissions and somehow convert them into 6Mz wide QAM (64QAM, maybe?). I think this was done in a single device, and if it is, such a device would seem to internally incorporate functionality comparable to, but not identical to, what sdossick wants to do, so the price of that device might be a guideline as far as the likely market price of an integrated QAM to 8VSB converter if anyone decides to produce such an animal using the prevailing commercial signal processing architecture.


But for member sdossick's purposes, the output of the R. L. Drake, Scientific Atlanta, or Blonder Tongue demodulator alone would probably be more useful than a reconstituted 8VSB stream, since it would, at that point, be in suitable form for viewing or recording. But that is what he can already get out of a consumer-grade QAM tuner, which costs less than any of the commercial product alternatives.


Analog broadcast NTSC signals can be economically converted to other broadcast and cable channels through a process called heterodyne conversion in which the broadcast signal is mixed with a fixed oscillator output while the NTSC analog content of the signal remains the same. The cost of such circuitry, which is used in all agile NTSC tuners to bring broadcast and cable TV channels down to so-called "intermediate frequency", is no more than a few dollars per mass-produced unit. But converting from QAM to 8VSB requires reprocessing the signal twice, first in the manner of its ordinary processing for viewing, and then in the manner ordinarily used for making this intermediate product suitable for transmission. There will never be significant demand for such a product so as to warrant its mass production, and its cost would always be greater than the cost of a simple demodulation device.
 

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Quote:
Originally posted by AntAltMike
Analog broadcast NTSC signals can be economically converted to other broadcast and cable channels through a process called heterodyne conversion in which the broadcast signal is mixed with a fixed oscillator output while the NTSC analog content of the signal remains the same.
Is this possible with 8VSB or does the conversion tear it up too much? I potentially have two channel 29's that I would like to try to tune once top 100 maximization occurs. I understand that the PSIP data might be a different problem insofar as confusing the tuner.
 

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Quote:
Originally posted by slykens
Is this possible with 8VSB or does the conversion tear it up too much?
Funny you should ask. A couple of years ago, I called a few manufacturers of analog heterodyne converters and asked them what would happen if I tried using what is commonly called an XUV converter on 8VSB signals, but none of them had a clue. Regrettably, if you call the customer service line of even top-of-the-line headend component manufacturers, you don't get to talk to their senior engineers.


Maybe if I ever have some free time on my hands, I'll try it myself. The XUV converter's input frequency is readily changable by anyone with a spectrum analyzer, so I could easily take one of my 26-6 analog converters, retune it to 27-6 to tune a local broadcast 8VSB signal, and then see what my WinTV-D card says it is seeing on that channel. If it finds it and locks onto it, I will also get to compare what it says is now the signal-to-noise ratio compared to what it was when I tuned the same 8VSB signal on its natural, broadcast channel.
 

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The Mits HD-5000 receives unscrambled QAM cable TV. It has firewire outputs. That should be relatively easy to display or record. I haven't tried it, so I'm not sure. My biggest concern would be if the cable company decided to turn on encryption... you're left with a $1500 paper weight.
 
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