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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