QAM seems to be a very frequently discussed topic here, and the same questions seem to be coming up repeatedly. Additionally, when QAM comes up in other threads, it often does so with some degree of misunderstanding. This FAQ is my attempt to gather all of the relevant information into one location. I certainly do not claim to be an expert in this field, and really am relying solely on information I have gleaned while reading many posts from others here at AVS Forum. It is by no means comprehensive (nor is it meant to be), but others can feel free to make suggestions for included content either on these pages or via PM. As such, this should be considered a work in progress and MAY CONTAIN MISTAKES (if so, hopefully these will be quickly corrected). As I live in the U.S., this document will naturally come from that perspective, although it will also apply to countries with DVB-C, as it too uses QAM.
1. What is QAM?
QAM stands for quadrature amplitude modulation, but the specifics of how it works are beyond the scope of this document (if you want more technical information, I suggest starting here). From a practical perspective relevant to HTPCs, it is the most common method by which cable companies transmit their digital cable offerings, including high definition (HD) content. If a computer's HDTV tuner has QAM capabilities it therefore MAY (see below) allow reception of HD signals from the cable provider. This reception then (theoretically) allows for recording, timeshifting, and other functionality often associated with HTPCs.
1a. Is all QAM the same?
No. First, there are two main flavors: QAM64 and QAM256 (which has both higher capacity and a greater susceptibility to noise than QAM64). QAM64 is used primarily for digital transmission of standard definition television signals, while QAM256 is used for HD signals. Some cards support QAM64 only, thus limiting their HDTV capabilities. Additionally, signals can be either scrambled or unscrambled, with the latter being required for HTPC reception. 2. What hardware supports QAM?
Most cards sold today claim to support QAM. At the hardware level, most (if not all) HDTV tuner cards do so (at least in theory). However, to fully support QAM, software support is also required.
3. What software supports QAM?
Essentially, we need to break down further our definition of software into low-level software (firmware and drivers) and application software (more specifically for our purposes, PVR software). In order to function properly, a card needs to have support in both software levels.
3a. What cards have drivers that support QAM?
For Windows (VFW/WDM):
DVICO Fusion III QAM
DVICO Fusion5 series
Hauppauge WinTV HVR-1600 (QAM is only supported on product codes 74021 and 74041, found on the tuner label)
Hauppauge WinTV HVR-1800
KWorld 115
MyHD MDP-130
OnAir Creator
OnAir GT
OnAir Sasem
For Windows (BDA):
Silicondust HDHomerun network tuner (external box that sends its signal via ethernet)
For Linux:
A good list can be found here (paying attention to the entries in the QAM row).
For Mac:
Elgato EyeTV 500
Miglia TV Mini HD
3b. What PVR applications support QAM?
For Windows:
Manufacturers who have WDM (or VFW) drivers that support QAM typically provide their own bundled software to access the QAM functionality. However, after a long wait, some 3rd party support does now exist (supported hardware in parentheses)
SageTV (OnAir GT, HDHomerun)
GB-PVR (OnAir GT, Hauppauge WinTV HVR-1600, HDHomerun)
Windows Media Center (HDHomerun only)
BeyondTV (HDHomerun only)
MediaPortal (HDHomerun only)
Cliff Watson Episode Program Guide (wrapper for the MyHD and FusionHDTV software)
For Linux:
MythTV
For Mac:
??? [any help on Mac stuff in particular would be appreciated]
3c. Why aren't there more options for hardware/software configurations? In other words, why doesn't my favorite PVR software work with my favorite tuner card?
This is a somewhat long and winding trail that leads back to Microsoft. Almost all third party Windows PVRs require BDA drivers. Card manufacturers create their BDA drivers based on the BDA spec. Currently, the BDA spec does not allow for direct QAM support (the HDHomerun is skirting around this through its unique interface). The creator/maintainer of the BDA spec is Microsoft. So, until the spec is updated to accomodate QAM, no card manufacturer is going to be able to write a QAM-enable BDA driver, which thus prevents any third party programs from accessing QAM. Unfortunately, it appears the release of Vista did little to clear up this mess, as was originally hoped. 4. Will QAM work with the set top box (STB) from my cable provider?
No. The STB will have no interaction with a QAM tuner card.
4a. Is there any other way to use my STB with my HTPC?
Possibly, by using the Firewire port. See this thread for more information. Note that if you go this route, you will NOT need a separate tuner card. 5. So if I meet the hardware/software requirements, I can use QAM to get my cable provider's HD channels on my HTPC, right?
Well, maybe, and this is where things can get really hairy. In short, it depends largely on the cable provider. QAM tuner cards can only tune unencrypted (or "clear") QAM stations, and stations currently vary widely in what they do and do not encrypt. Some users can receive everything (OTA networks, ESPN, TNT, etc), although this number is decreasing. Some can receive nothing (though this may be in violation of the FCC). Once the cable companies get all of the kinks worked out, one can probably expect to receive, in unencrypted form, the OTA channels and not much (if anything) else.
Additionally, there is a dependence on which frequencies the cable providers are using to transmit their channels. Some configurations have limitations on which frequencies are accessible.
One final note should be made about configurations. Even if the cable company is providing unencrypted stations on accessible frequencies, and even though the users have compliant software and hardware, some have still reported great difficulty in configuring their computers to receive such channels. Therefore the user is advised that, even with a compliant configuration, setup may not be trivial.
1. What is QAM?
QAM stands for quadrature amplitude modulation, but the specifics of how it works are beyond the scope of this document (if you want more technical information, I suggest starting here). From a practical perspective relevant to HTPCs, it is the most common method by which cable companies transmit their digital cable offerings, including high definition (HD) content. If a computer's HDTV tuner has QAM capabilities it therefore MAY (see below) allow reception of HD signals from the cable provider. This reception then (theoretically) allows for recording, timeshifting, and other functionality often associated with HTPCs.
1a. Is all QAM the same?
No. First, there are two main flavors: QAM64 and QAM256 (which has both higher capacity and a greater susceptibility to noise than QAM64). QAM64 is used primarily for digital transmission of standard definition television signals, while QAM256 is used for HD signals. Some cards support QAM64 only, thus limiting their HDTV capabilities. Additionally, signals can be either scrambled or unscrambled, with the latter being required for HTPC reception. 2. What hardware supports QAM?
Most cards sold today claim to support QAM. At the hardware level, most (if not all) HDTV tuner cards do so (at least in theory). However, to fully support QAM, software support is also required.
3. What software supports QAM?
Essentially, we need to break down further our definition of software into low-level software (firmware and drivers) and application software (more specifically for our purposes, PVR software). In order to function properly, a card needs to have support in both software levels.
3a. What cards have drivers that support QAM?
For Windows (VFW/WDM):
DVICO Fusion III QAM
DVICO Fusion5 series
Hauppauge WinTV HVR-1600 (QAM is only supported on product codes 74021 and 74041, found on the tuner label)
Hauppauge WinTV HVR-1800
KWorld 115
MyHD MDP-130
OnAir Creator
OnAir GT
OnAir Sasem
For Windows (BDA):
Silicondust HDHomerun network tuner (external box that sends its signal via ethernet)
For Linux:
A good list can be found here (paying attention to the entries in the QAM row).
For Mac:
Elgato EyeTV 500
Miglia TV Mini HD
3b. What PVR applications support QAM?
For Windows:
Manufacturers who have WDM (or VFW) drivers that support QAM typically provide their own bundled software to access the QAM functionality. However, after a long wait, some 3rd party support does now exist (supported hardware in parentheses)
SageTV (OnAir GT, HDHomerun)
GB-PVR (OnAir GT, Hauppauge WinTV HVR-1600, HDHomerun)
Windows Media Center (HDHomerun only)
BeyondTV (HDHomerun only)
MediaPortal (HDHomerun only)
Cliff Watson Episode Program Guide (wrapper for the MyHD and FusionHDTV software)
For Linux:
MythTV
For Mac:
??? [any help on Mac stuff in particular would be appreciated]
3c. Why aren't there more options for hardware/software configurations? In other words, why doesn't my favorite PVR software work with my favorite tuner card?
This is a somewhat long and winding trail that leads back to Microsoft. Almost all third party Windows PVRs require BDA drivers. Card manufacturers create their BDA drivers based on the BDA spec. Currently, the BDA spec does not allow for direct QAM support (the HDHomerun is skirting around this through its unique interface). The creator/maintainer of the BDA spec is Microsoft. So, until the spec is updated to accomodate QAM, no card manufacturer is going to be able to write a QAM-enable BDA driver, which thus prevents any third party programs from accessing QAM. Unfortunately, it appears the release of Vista did little to clear up this mess, as was originally hoped. 4. Will QAM work with the set top box (STB) from my cable provider?
No. The STB will have no interaction with a QAM tuner card.
4a. Is there any other way to use my STB with my HTPC?
Possibly, by using the Firewire port. See this thread for more information. Note that if you go this route, you will NOT need a separate tuner card. 5. So if I meet the hardware/software requirements, I can use QAM to get my cable provider's HD channels on my HTPC, right?
Well, maybe, and this is where things can get really hairy. In short, it depends largely on the cable provider. QAM tuner cards can only tune unencrypted (or "clear") QAM stations, and stations currently vary widely in what they do and do not encrypt. Some users can receive everything (OTA networks, ESPN, TNT, etc), although this number is decreasing. Some can receive nothing (though this may be in violation of the FCC). Once the cable companies get all of the kinks worked out, one can probably expect to receive, in unencrypted form, the OTA channels and not much (if anything) else.
Additionally, there is a dependence on which frequencies the cable providers are using to transmit their channels. Some configurations have limitations on which frequencies are accessible.
One final note should be made about configurations. Even if the cable company is providing unencrypted stations on accessible frequencies, and even though the users have compliant software and hardware, some have still reported great difficulty in configuring their computers to receive such channels. Therefore the user is advised that, even with a compliant configuration, setup may not be trivial.
I receive all the locals, and a few others that aren't encrypted.
)
