Mailing List Archive: Maximum QAM frequency with HVR-1600?

Maximum QAM frequency with HVR-1600?

Apr 21, 2011, 10:59 AM

Post #1 of 5 (3402 views)

I've been using the dvb-apps tools to scan for new clean QAM channels in my area on my HVR-1600, and noticed that the frequencies listed in /usr/share/dvb/atsc/us-Cable-Standard-center-frequencies-QAM256 only go up to 801000000, or us-cable channel 125. I also observed that when I scan for channels on my hdhr, using their hdhomerun_config utility, that the max frequency it scans is 861000000, or us-cable 135. So I thought I'd try scanning my HVR-1600 for the same frequencies that hdhomerun_config uses. The driver rejects a couple of the frequencies with the dmesg:

DVB: adapter 0 frontend 0 frequency 861000000 out of range (54000000..858000000)

So I did a little googling, trying to figure out what are valid QAM frequencies, and came across this article:

http://en.wikipedia.org/wiki/North_American_cable_television_frequencies

The table for North American cable tv frequencies in that article goes up to channel 158, QAM frequency 999.00 MHz. The article also says:

"Many cable providers currently don't distribute any video content above channel 139, or about 900MHz. As of 2009, it is common for TVs in North America with built in tuners to not search analog or digital channels above channel 139. Most TVs made before 2005 do not include a QAM tuner, and only have an analog cable tuner which often cannot tune beyond channel 125. With the addition of services such as premium HD content, cable providers such as Cox Communications and Insight Communications have begun to roll out digital cable services which use frequencies up to 1Ghz (analog channel 158), while also dropping the analog channel formats."

So, my questions are:

- Shouldn't I be able to tune frequencies up to 900 MHz, cable channel 139?

- Is the limit mentioned in the dmesg output imposed by the driver software or by the hardware?

- If it's driver software, should it be increased, maybe even up to 999 MHz, channel 158?

- I'm using Ubuntu 10.10, kernel 2.6.35-28-generic. Could it be the upper limit has been increased in the latest v4l-dvb drivers?

Inquiring minds want to know,
Helen

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Re: Maximum QAM frequency with HVR-1600? [ In reply to ]

dheitmueller at kernellabs

Apr 21, 2011, 11:06 AM

Post #2 of 5 (3349 views)

Permalink

On Thu, Apr 21, 2011 at 1:59 PM, faginbagin <mythtv@hbuus.com> wrote:
> I've been using the dvb-apps tools to scan for new clean QAM channels in my
> area on my HVR-1600, and noticed that the frequencies listed in
> /usr/share/dvb/atsc/us-Cable-Standard-center-frequencies-QAM256 only go up
> to 801000000, or us-cable channel 125. I also observed that when I scan for
> channels on my hdhr, using their hdhomerun_config utility, that the max
> frequency it scans is 861000000, or us-cable 135. So I thought I'd try
> scanning my HVR-1600 for the same frequencies that hdhomerun_config uses.
> The driver rejects a couple of the frequencies with the dmesg:
>
> DVB: adapter 0 frontend 0 frequency 861000000 out of range
> (54000000..858000000)
>
> So I did a little googling, trying to figure out what are valid QAM
> frequencies, and came across this article:
>
> http://en.wikipedia.org/wiki/North_American_cable_television_frequencies
>
> The table for North American cable tv frequencies in that article goes up to
> channel 158, QAM frequency 999.00 MHz. The article also says:
>
> "Many cable providers currently don't distribute any video content above
> channel 139, or about 900MHz. As of 2009, it is common for TVs in North
> America with built in tuners to not search analog or digital channels above
> channel 139. Most TVs made before 2005 do not include a QAM tuner, and only
> have an analog cable tuner which often cannot tune beyond channel 125. With
> the addition of services such as premium HD content, cable providers such as
> Cox Communications and Insight Communications have begun to roll out digital
> cable services which use frequencies up to 1Ghz (analog channel 158), while
> also dropping the analog channel formats."
>
> So, my questions are:
>
> - Shouldn't I be able to tune frequencies up to 900 MHz, cable channel 139?
>
> - Is the limit mentioned in the dmesg output imposed by the driver software
> or by the hardware?
>
> - If it's driver software, should it be increased, maybe even up to 999 MHz,
> channel 158?
>
> - I'm using Ubuntu 10.10, kernel 2.6.35-28-generic. Could it be the upper
> limit has been increased in the latest v4l-dvb drivers?
>
> Inquiring minds want to know,
> Helen

Hello Helen,

These are all good questions and frankly I had never really given it
much thought. I can tell you that the limit is "enforced" by the
demodulator driver (assuming you have an older HVR-1600, we're talking
about the s5h1409). That said, we would have to look at the
datasheets for the 1409 as well as the mxl5005s to see what they can
actually support in terms of frequency range. And then it's also
possible that driver changes would be required beyond just increasing
the maximum value.

Were you able to actually find any valid signals above 125?

Devin

--
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com

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Re: Maximum QAM frequency with HVR-1600? [ In reply to ]

dheitmueller at kernellabs

Apr 21, 2011, 11:22 AM

Post #3 of 5 (3352 views)

Permalink

On Thu, Apr 21, 2011 at 1:59 PM, faginbagin <mythtv@hbuus.com> wrote:
> So, my questions are:
>
> - Shouldn't I be able to tune frequencies up to 900 MHz, cable channel 139?

The doc I'm looking at suggests that the mxl5005s can support up to
900MHz. So we probably could increase the cap and it would work,
although the hardware cannot support 900-1GHz.

Also, double checked the Linux driver sources, and at first glance it
does look like it is setting the DN_IQTNBUF_AMP and
DN_IQTNGNBFBIAS_BST properly for frequencies between 800-900Mhz.

Devin

--
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com

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Re: Maximum QAM frequency with HVR-1600? [ In reply to ]

awalls at md

Apr 21, 2011, 2:54 PM

Post #4 of 5 (3358 views)

Permalink

On Thu, 2011-04-21 at 13:59 -0400, faginbagin wrote:
> I've been using the dvb-apps tools to scan for new clean QAM channels in my area on my HVR-1600, and noticed that the frequencies listed in /usr/share/dvb/atsc/us-Cable-Standard-center-frequencies-QAM256 only go up to 801000000, or us-cable channel 125. I also observed that when I scan for channels on my hdhr, using their hdhomerun_config utility, that the max frequency it scans is 861000000, or us-cable 135. So I thought I'd try scanning my HVR-1600 for the same frequencies that hdhomerun_config uses. The driver rejects a couple of the frequencies with the dmesg:
>
> DVB: adapter 0 frontend 0 frequency 861000000 out of range (54000000..858000000)
>
> So I did a little googling, trying to figure out what are valid QAM
> frequencies, and came across this article:
>
> http://en.wikipedia.org/wiki/North_American_cable_television_frequencies
>
> The table for North American cable tv frequencies in that article goes
> up to channel 158, QAM frequency 999.00 MHz. The article also says:

Hmmm.

ITU-T J.83 Annex B 2007-12:

http://www.itu.int/rec/T-REC-J.83-200712-I

specifies a freq range of 54-860 MHz.

The FCC's part of the Code of Federal Regulations for this, Title 47 CFR
Part 76 Section 76.605(a)(1)(ii):

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=b4ac42997368c3adac19879b5fd27dbc&rgn=div8&view=text&node=47:4.0.1.1.4.11.3.3&idno=47

incorporates the channel plan in CEA-542-B by reference.

CEA-542-C looks like it goes up to 1002 MHz or up to channel 158:

http://www.ce.org/Standards/browseByCommittee_2549.asp

All the freely available information I can find on CEA-542-A/B/C or
EIA-542 suggests that the high end of the last channel (158) is at 1002
MHz, making the center freq of that 6 MHz channel to be 999 MHz.

> "Many cable providers currently don't distribute any video content
> above channel 139, or about 900MHz. As of 2009, it is common for TVs
> in North America with built in tuners to not search analog or digital
> channels above channel 139. Most TVs made before 2005 do not include a
> QAM tuner, and only have an analog cable tuner which often cannot tune
> beyond channel 125. With the addition of services such as premium HD
> content, cable providers such as Cox Communications and Insight
> Communications have begun to roll out digital cable services which use
> frequencies up to 1Ghz (analog channel 158), while also dropping the
> analog channel formats."
>
> So, my questions are:
>
> - Shouldn't I be able to tune frequencies up to 900 MHz, cable channel 139?

Well, 860 MHz is the center freq of channel, I think, 135 under CEA-542.
So equipment strictly complying with ITU-T J.83 Annex B need not work
there; of course manufacturers can choose to do so.

> - Is the limit mentioned in the dmesg output imposed by the driver
> software or by the hardware?

Driver software, which may or may not in turn be driven by hardware
specifications for the MXL5005s tuner chip and the design of any
external filters that the hardware requires.

Also note that coaxial cable attenuation in dB/100 ft. can be
non-trivial at 1000 MHz.

MIL-DTL-17/2A-RG6 specifies
6.5 dB/100 ft @ 400 MHz
23.0 dB/100 ft @ 3000 MHz
(10.3 dB/100 ft @ 1000 MHz using linear interpolation)
http://www.assistdocs.com/search/document_details.cfm?ident_number=941&StartRow=1&PaginatorPageNumber=1&doc_id=MIL-DTL-17%2F2&status_all=ON&search_method=BASIC

MIL-DTL-17/29C-RG59 specifies
9.0 dB/100 ft @ 400 MHz
16.0 dB/100 ft @ 1000 MHz
http://www.assistdocs.com/search/document_details.cfm?ident_number=956&StartRow=1&PaginatorPageNumber=1&doc_id=MIL-DTL-17%2F29&status_all=ON&search_method=BASIC

> - If it's driver software, should it be increased, maybe even up to
> 999 MHz, channel 158?

As Devin said, as long as it is the chip's operational range (i.e. won't
melt when programmed for such), the limit can be raised.

Acceptable performance at those freq's will be the question. Users
should ensure they have good cabling, connectors, splitters that cover
the entire band, and proper grounding of the cable shielding.

Also someone with access to the s5h1409 and mxl5005s datasheets, and
knowledge of the external component wire-up around the mxl5005s will
need to review how the linux drivers program the chips at those freqs.

> - I'm using Ubuntu 10.10, kernel 2.6.35-28-generic. Could it be the
> upper limit has been increased in the latest v4l-dvb drivers?

I don't think anyone's touched the s5h1409 and mxl5005s drivers in quite
a while.

Regards,
Andy

> Inquiring minds want to know,
> Helen

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Re: Maximum QAM frequency with HVR-1600? [ In reply to ]

mythtv at hbuus

Apr 21, 2011, 3:56 PM

Post #5 of 5 (3350 views)

Permalink

Hi Devin,

On 4/21/2011 2:06 PM, Devin Heitmueller wrote:
<snip>
> Were you able to actually find any valid signals above 125?
>
> Devin

The HDHR found 5 clear QAM channels on 126, 807000000, and from a quick viewing in the wee hours, they seem to be local access type stuff. But who knows if more interesting channels will be added at the higher frequencies as WOW goes through their digital transition. The HVR-1600 didn't see them. Probably not its fault, it's got more splitters in the way. I'm hoping to test both of my HVR-1600s, one at a time, in a room that eliminates two splitters in the next few days.

I've been looking into this because my cable provider, WOW, is getting serious about digital starting mid-May and I'm thinking about doing some rewiring and relocating of the HVR-1600s so I can get full use out of them. Right now, I'm only using the digital half on one card and analog on both. The one card I'm using for digital can only see about half the QAM channels that the hdhr and our HDTVs can see.

Since the drivers do support up to channel 134, do you think someone should update the data files that are included with dvb-apps like us-Cable-Standard-center-frequencies-QAM256 to at least go up to 134? Seems to me that, as the files stand, cable subscribers might not be seeing all the channels they should with their dvb devices.

Many thanks to you and Andy for answering my questions,

Helen

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