a QAM FAQ

[ORPhD]

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.

[Commodore 64]

Basically, with all the QAM questions it seems to me that people are searching for a solution that will allow them to view and record digital content from cable companies. Basically, unless you are lucky, it really doesn't do anything for you unless you can't get OTA channels. Once the cable companies get their ducks in a row, you aren't going to get anything unecrypted other than what the law says must be unencrypted...and that is local OTA channels.

It seems ridiculous to me that in order to get digital TV out to a PC (arguably the biggest influence on digital media) whether it be by satellite or cable, you have to port it through an analog connection.

QAM is a gold pot at the end of a rainbow.

[madpoet]

Good start! Some additions to the FAQ:

QAM has two flavors, QAM64 and QAM256. QAM64 is typically used to convey the digital simulcast stations, your cable company's music channels, and other SD material. QAM256 is used primarily for High Definition signals. Both QAM64 and QAM256 will put a number of subchannels on the same primary channel number. In the case of QAM64 this could be dozens of channels under one number (i.e. 100-1 through 100-40). QAM256 typically limits channels with high definition material to only 2 subchannels, although some cable companies have been known to use 3. The more subchannels used the less bandwidth each individual channel is afforded.

Additionally, not all cards can tune both QAM64 and QAM256, and even if they are capable of both some cannot do them at the same time. The MyHD130 is capable of tuning both levels simultaneously.

[Munkee Boy]

Originally Posted by ORPhD

What hardware supports QAM?

[Note: I am likely missing several here and would greatly appreciate being told of any such omissions]

For Windows:
DVICO Fusion III QAM
DVICO Fusion5 series
AVerMedia AVerTVHD MCE A180
MyHD MDP-130
VBox Cat's Eye 164e (not yet released as of 5/4/06)

For Linux:
DVICO Fusion III QAM
DVICO Fusion5 series
pcHDTV HD3000
pcHDTV HD5500
AirStar-HD5000AV

As far as I know, Shimon, the VBox rep that visits these forums, has come out and said that the Cat's Eye 164e will not support QAM.

[ORPhD]

Originally Posted by Munkee Boy

As far as I know, Shimon, the VBox rep that visits these forums, has come out and said that the Cat's Eye 164e will not support QAM.

Actually, I'm pretty sure this was his most recent comment on the matter:

Originally Posted by Shimon Hirschorn

I ask because QAM 64 is easier than QAM 256 and like everyone else we have finite development capabilities. We will have QAM support. The question is how many people does this satisfy.

So I guess I would still chalk this one up to "up in the air." But considering how just about every other card with QAM capabilities has some current issues, I figure I'll leave it up there for now.

madpoet: I had considered adding QAM64 and QAM256 stuff, but didn't know enough about it yet. This certainly provides a start. I should include it in a future update.

[Munkee Boy]

Originally Posted by ORPhD

Actually, I'm pretty sure this was his most recent comment on the matter:



So I guess I would still chalk this one up to "up in the air." But considering how just about every other card with QAM capabilities has some current issues, I figure I'll leave it up there for now.

If you read the rest of the thread, I believe that post was referring to another card they have in development that is CableCard compliant. I guess time will tell. Supposedly, the card is supposed to hit retail in the next 3-4 weeks.

[Munkee Boy]

I only have plain old analog cable, no cable boxes for me. I'd like to keep it that way for as long as possible. Also, I live in an apartment, so don't really have the option to mount an antenna for the HD channels. This is why QAM is my best friend. I receive all the locals, and a few others that aren't encrypted.

[RTK]

Do any of the PVR software applications support QAM tuners?

[CityK]

Originally Posted by ORPhD

I look forward to any critiquing.

I appluad your effort. Here are some thoughts.

I live in the U.S., I (currently) have no idea how much or how little of this will apply to other countries.

It applies equally to countries which use DVB-C; given DVB-C utilizes QAM too....so,

From a practical perspective relevant to HTPCs, it is the method by which cable companies transmit their digital cable offerings, including high definition (HD) content.

is a good general statement...you might want to include a comment that QAM need not be the modulation scheme employed (as others can, do and have been used), but that it is the defacto method.

If a computer's HDTV tuner has QAM capabilities it therefore MAY (see below) allow reception of HD signals from the cable provider

excellent !

2. What hardware supports QAM?

[Note: I am likely missing several here and would greatly appreciate being told of any such omissions]

All DTV pc cards (aimed at the N.A market) that I am aware of have hardware that supports the demodulation of QAM.

That being said, in order to realize or succesfully recieve a digital cable signal you need three components to come together:
- hardware that can support this function (i.e demodulation of a signal employing QAM) and that is properly implemented into the device design
- low level software (drivers, firmware) that can make that hardware level support/function available to userspace apps
- userspace apps that are written to make use of such services

Deviate from that, and it won't work. Examples:
- pcHDTV HD-2000: without the firmware, it's useless for these purposes
- Aver A180: works in Linux cause the drivers support it, but doesn't currently have Windows support
- Dvico F3G (i.e the first of three variants): board level design seemed to perclude much in the way of success with QAM256 sources
- etc etc

As for your list, it doesn't make logical sense -- your talking about the hardware that supports QAM...why would you seperate it into OS platforms?

If you meant it as a fully supported list (i.e. meets criteria mentioned above), then you should remove the Aver from the Windows list, add the (ever overlooked) OnAir products, and the Dvico F3G QAM-T...I would also remove the VBox, until it becomes clear what they are going to do. For Linux support, this is mostly correct. The list neglects the HD-2000 (which isn't relevant to this "fully supported" discussion anyways), and is of course lacking the yet released pcHDTV HD-5500 ... the OnAir devices will make there way on there soon enough too ( - in case ryan is reading this, I announce this publically only because Michael has mentioned it on the mailing list a couple of times now, so I figure its as good as wild ow )

Don't overlook Mac's too (else Mac zealot's might start beating there war drum ) Elgato and what ever else (believe Fusion3's work on OS X too )

3. What software supports QAM?

You might want to define what you mean by software.

Drivers? Here's a good place to talk about BDA drivers...And how Dvico, MIT, and OnAir drivers work in windows...also, Twinhan's BDA.

Apps - do you mean any viewing app or specifically PVR?

In fact, (to this author) the only known program with current QAM support for HDTV cards from multiple manufacturers is the MythTV project for Linux.

There are several apps and utilities you can use in Linux; such as mplayer, xine, some from the dvb-apps etc ... that will stream, record etc. In terms of PVR style, besides myth, I believe VDR supports DVB-C...Freevo might too.

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.

You might want to expand on this...we get a billion and one threads about this....if you do tackle this one, and discuss the prosumer/pro cards that can accept the output from a STB, you might want to discuss how this really falls outside the realm of htpc...stanger89 had a good laundry list of points on this not too long ago.

got to run ... maybe more later

[RTK]

Originally Posted by ORPhD

Is this not answered in question 3, or do I need to phrase something differently?

Since you asked, You should add a phrase to your FAQ that specifically states that Windows PVR apps such as SageTV, BTV, MeedioTV, and MCE do not support QAM tuning/recording at this time. I do not know this to be the case but am drawing the conclusion based upon your comments.

[RalphArch]

Originally Posted by mechou

In addition, I presented both technical and economical reasons why firewire recording with STB makes more sense. You have yet to rebut those reasons by showing how a QAM PC card is superior to recording firewire off the STB.

Having recorded via firewire (Motorola PVR STB) and simultaneously recorded via QAM card (MyHD MDP 130) for years - all I can say is that my experience is exactly like Madpoet's.

I have given up on the firewire approach even though it works and the about same set of channels are available to me as it is just so much more convenient to use the recording features of the PC card.

Before 5c was implememted it made sense - now this discussion really doesn't belong in a QAM thread due to cludginess of the firewire approach and general lack of support and interest.

[Shimon Hirschorn]

Hi,

Sorry I missed the debate about QAM vs Firewire (not).

The Cat's Eye 164e is supposed to support QAM 64. I have yet to test this fully so I am not sure. The first version of the card will not support QAM 256. We are working on solving this problem. It is requires a change to hardware as well as a version of BDA that Microsoft has not yet released.

Shimon Hirschhorn
VBox Communications

[Dick Kalagher]

I don't know if anyone mentioned this (I did not see it) but your DTV card must be able to tune to the frequencies where the local DTV signal is. Most cards only go up to 800 MHz. In Fairfax County, VA, for one, Cox cable puts several local channels above this frequency.

[Joseph S]

For Mac OS X:
EyeTV 500
Miglia TV Mini HD

[RalphArch]

Originally Posted by Shimon Hirschorn

Hi,

Sorry I missed the debate about QAM vs Firewire (not).

The Cat's Eye 164e is supposed to support QAM 64. I have yet to test this fully so I am not sure. The first version of the card will not support QAM 256. We are working on solving this problem. It is requires a change to hardware as well as a version of BDA that Microsoft has not yet released.

Shimon Hirschhorn
VBox Communications

Seems like releasing such a card would be a big mistake. For example my COMCAST system is fully QAM 256, even the ADS channels.


Think of all the disgruntled buyers you will have when they discover its useless for them

[ORPhD]

Sorry for taking a couple days off from the thread, although I was still reading all that transpired. It was just that, in order to enjoy surround sound in my home for the first time in over two years, I spent the weekend running speaker wire...and some things just take precedent over some document that I whipped up during down time at work.

CityK: Thanks for the many absolutely excellent suggestions (especially pointing out my careless OS/hardware mistake...oops). I think just about every suggestion you made will be incorporated in some manner as I find time. You also serendipitously solved a few organization-related problems I was having. So thanks.

Shimon: Thank you for the clarification. Your participation on this forum is greatly appreciated.

Mac addicts: Thanks for not getting all riled up at my (entirely accidental) original omission. I certainly don't want to exclude you.

Everyone: All the suggestions have been appreciated and duly noted. Now let's just try to remain civil and on topic

-dave

[SlicerDicer]

somebody posted some legal citations earlier regarding local HDTV tier by by cable. What happened to those posts? were they moved?

[CityK]

Originally Posted by Dick Kalagher

I don't know if anyone mentioned this (I did not see it) but your DTV card must be able to tune to the frequencies where the local DTV signal is. Most cards only go up to 800 MHz. In Fairfax County, VA, for one, Cox cable puts several local channels above this frequency.

This is a good point, however a distinction must be made: all available cards/devices have hardware capable to tuning to ~865MHz, but not all software (in particular, that for Windows OS) supports this ability. Examples include the situation for the MIT and Dvico cards...although I think, but am not sure (nor really care), that Terry eventually contacted both co.'s about adjusting this facet...perhaps its already been addressed.

[CityK]

Originally Posted by SlicerDicer

somebody posted some legal citations earlier regarding local HDTV tier by by cable. What happened to those posts? were they moved?

I don't think they survived Bob's knife

They were all taken from http://www.fcc.gov/dtv/ , so easily recovered if necessary.

[SlicerDicer]

Originally Posted by CityK

I don't think they survived Bob's knife

They were all taken from *snip* , so easily recovered if necessary.

Why were they removed if they were cited from fcc.gov? I am just wondering I browse this site quite often and check what the latest info is. I noticed that this was removed so figured I would ask why useful information was being removed. No matter if it was easy to be recovered.

[CityK]

ORPhD/dave,

If others are interested about cable reception with other devices on mac OSes, it likely is contained in http://www.defyne.org/dvb/driver.html (in their forum)...I'm not looking

Another thought is perhaps a brief discussion on the lack of uniformity in regards to the broadcast systems used by different cable networks....the (Opencable/SCTE) goal of moving towards a common standard.

[CityK]

Originally Posted by SlicerDicer

Why were they removed if they were cited from fcc.gov? I am just wondering I browse this site quite often and check what the latest info is. I noticed that this was removed so figured I would ask why useful information was being removed. No matter if it was easy to be recovered.

Couldn't tell you Slicer ... hence kidding about not surving Bob's (or whatever moderator's) knife ... I just guess that, instead of a surgical approach, whomever did the editing preferred to slash ... they likely have their reasons, but I can't speak for them

[KAXKID]

Originally Posted by CityK

This is a good point, however a distinction must be made: all available cards/devices have hardware capable to tuning to ~865MHz, but not all software (in particular, that for Windows OS) supports this ability. Examples include the situation for the MIT and Dvico cards...although I think, but am not sure (nor really care), that Terry eventually contacted both co.'s about adjusting this facet...perhaps its already been addressed.

we have been able to work around this software limitation by reassigning freqs to unused channel numbers in the registry via the tv services tuning spaces.

[TPeterson]

Originally Posted by CityK

...[A] distinction must be made: all available [QAM] cards/devices have hardware capable to tuning to ~865MHz, but not all software (in particular, that for Windows OS) supports this ability. Examples include the situation for the MIT and Dvico cards....

On the Fusion cards, as KAXKID noted, there is a Registry hack to allow access to channels rf 126-135 (~800 to ~860 MHz). I don't know if DViCO will eventually retool their sw to make this unnecessary, but it seems likely...eventually.

The MDP-130's tuner is capable of tuning to rf 135 but the software was designed to stop at rf 125 because there were no known cableco HD stations above that last year. MyHD's manufacturer says that the sw limit can and will be removed, but it's not yet implemented.

[netman]

Originally Posted by SlicerDicer

Why were they removed if they were cited from fcc.gov? I am just wondering I browse this site quite often and check what the latest info is. I noticed that this was removed so figured I would ask why useful information was being removed. No matter if it was easy to be recovered.

There was a lot of rancor that had developed around an off topic branching of the thread. It looks like someone (with a lot of sense) cut all that stuff out leaving a nice clean discussion again about the actual topic of the thread. I assume the stuff you mention was victim to that and not offensive on its own accord. Of course I could always be wrong.

[madpoet]

The stuff you are looking for had absolutely nothing to do with a QAM faq.

[Shimon Hirschorn]

Hi,

I just read about this registry hack for frequency adjustment. Can someone send me more information about this. I can be PM or any other way you know of getting in touch with me. This hack would be very helpful to me to test something that we are working on right now.

I apprecieate the help

Shimon Hirschhorn
Vbox Communications

[ORPhD]

OK, based on both suggestions and self-critiquing, I made some fairly significant revisions to both content and layout. I guess we can now consider this to be version 0.1 alpha.

I tried to mostly add things that I could confirm either through more than one user making the same (or similar) statements, or via Google. I also may include some more with relation to the intricacies of accessing a cable box, but that will have to wait for a future version.

There are still a couple of things which I felt I needed more information about before including them...

-The Twinhan card(s): do these have BDA drivers that support QAM? Is that support just for DVB? I realize I need to research these more, but if someone can save me some time, I'd appreciate it.

@madpoet: you mentioned some cards cannot tune QAM256 and QAM64 simultaneously. I am very confused by this statement. Are you referring to two separate cards (guessing not), or two tuners in one card (I didn't realize the MyHD had this), or something else? I didn't think a single station could be both flavors at once.

Anyway, after tomorrow afternoon, my schedule over the next few weeks will be much more uncertain, so if there are any quick suggestions or major errors, I would need to be told of them by that time...otherwise they may have to wait a bit.

Thanks again for all the help.

[TPeterson]

Originally Posted by Shimon Hirschorn

Hi,

I just read about this registry hack for frequency adjustment. Can someone send me more information about this. I can be PM or any other way you know of getting in touch with me. This hack would be very helpful to me to test something that we are working on right now.

I apprecieate the help

Shimon Hirschhorn
Vbox Communications

Shimon--

Check the links in this post, especially the discussion that is linked in the BTV forum.

[madpoet]

Originally Posted by ORPhD

@madpoet: you mentioned some cards cannot tune QAM256 and QAM64 simultaneously. I am very confused by this statement. Are you referring to two separate cards (guessing not), or two tuners in one card (I didn't realize the MyHD had this), or something else? I didn't think a single station could be both flavors at once.

Not seperate tuners or cards. It is (usually) a software limitation. A QAM tuner (the hardware) has the capability to tune both sets of frequencies, but most vendors seem to have problems getting QAM64 to tune correctly in software. The MYHD can tune both bands at the same time. The Fusion series cards can tune one or ther other but not both. I am not sure on the rest. What this means in practical terms is, with the Fusion for example, you have to decide which band to use or you have to use more than one card (one for 64 and one for 256).