QAM

[traker1001]

Im new, could someone please explain qam to me?

[stanger89]

As far as what it means, it means digital cable.

As for what it actually is. It's a digital modulation technique that uses phase and amplitude to carry many bits with a single "symbol", up to 8 bits in fact with current QAM 256. That modulation is used to carry a (usually) MPEG-2 transport stream to your cable set top box.

Over the Air digital uses 8VSB modulation, which is a form of AM modulation, but capable of 3 bits/symbol.

Satellite uses QPSK for most things, which uses only phase for storing information, and can carry 2 bits/symbol, or 8PSK, again 3 bits/symbol.

Satellite and OTA are limited to the "order" of modulation they can use because they are susceptible to a great deal of noise, and as you increase the number of types of symbol used, it gets exceedingly hard to determine what those symbols are supposed to mean.

Cable can get away with much higher "orders" of modulation because it's comparatively much cleaner, far less susceptible to outside noise. That means it's easier to design recievers that can distinguish between 256 phase/amplitude combinations.

FWIW there's a neat plot of a 4-QAM waveform part way down this page:
http://zone.ni.com/devzone/cda/epd/p/id/5155

[mayamaniac]

The way I understood it in idiot terms or meaning, its the unencrypted HD channels you get from your cable/satellite company, which you can record with SageTV without needing a set top box (STB) and as long as your HD tuner card has QAM capabilities.

More explanation here: http://www.hdtvtunerinfo.com/hdtvpctunerqam.html

[traker1001]

I understand it now, Unfotunatly it doesnt seem to do me any good, As I am on sat and cable around here digital or otherwise is horrible. Thanks guys for explaining it to me.

[AngelofDeth]

Originally Posted by traker1001

I understand it now, Unfotunatly it doesnt seem to do me any good, As I am on sat and cable around here digital or otherwise is horrible. Thanks guys for explaining it to me.

You can capture satellite (Dish and DTV), but its not cheap. You can either buy or have an existing STB modifed with a USB2 port on it, and capture all channels. But its not cheap.

http://forums.sagetv.com/forums/show...ighlight=r5000

[traker1001]

I beleive I heard DTV was working with M$ on doing something about this, I may be wrong though. On any note, I am happy with my stand alone HD box and sage doing analog for now