[linux-dvb] cx88-dvb driver bug: unable to lock on some lower frequencies which have unencrypted channels

Matthew Schultz mattsch at gmail.com
Wed Feb 21 15:58:55 CET 2007


I just got my 4-way PCT Drop Amp yesterday and I must say that I am
impressed.  It really does improve the signal strength.  Now almost every
dvb frequency has the highest strength signal.  549Mhz, the most problematic
frequency, is locking every time.   It used to fluctuate but now it is
getting at least a weak lock every time.  I am curious as to why it is still
weak while all the other frequencies are much stronger.  As a result of this
weak lock, I will get pixelation when watching channels on this frequency
from time to time on mplayer.  Are there any software optimizations that can
improve the signal strength of this frequency since it is on a +8db drop
amp?


tuning to 543000000 Hz
video pid 0x0025, audio pid 0x0026
status 00 | signal 4b11 | snr 0a43 | ber 00000000 | unc 0000ffff |
status 1f | signal f2dc | snr 2134 | ber 00000000 | unc 0000ffff |
FE_HAS_LOCK
status 1f | signal f0d4 | snr 20ed | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal ef16 | snr 20b0 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal f01e | snr 20e3 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal f33e | snr 20f0 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal f008 | snr 20d1 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK

tuning to 549000000 Hz
video pid 0x0401, audio pid 0x0402
status 00 | signal 4b11 | snr 0a43 | ber 00000000 | unc 0000ffff |
status 1f | signal cb84 | snr 1bd3 | ber 00000000 | unc 0000ffff |
FE_HAS_LOCK
status 1f | signal caf1 | snr 1bbf | ber 00000000 | unc 00000030 |
FE_HAS_LOCK
status 1f | signal cb53 | snr 1bcc | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal caea | snr 1bbe | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cc1a | snr 1bba | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cc05 | snr 1be4 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cb53 | snr 1bcc | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cbbd | snr 1bda | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cab3 | snr 1bb6 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status 1f | signal cb7d | snr 1bc5 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK

On 2/18/07, Matthew Schultz <mattsch at gmail.com> wrote:
>
> I was talking to Michael Krufky the other day on the v4l irc channel and
> he mentioned a major problem when he got his first tuner card.  He said his
> apartment building was split so many times that the signal he was receiving
> was really weak.  He could only receive fox.  He mentioned that he got a
> drop amp to boost the signal.  As soon as he got that he was able to receive
> all the channels he couldn't receive before without the amp.
>
> He said that I should get an amp after he saw the signal fluctuation on
> especially 543 Mhz but he said that it may or may not fix the problem.  I
> decided to get a 4-way PCT Drop Amp on eBay similar to the 8-way drop amp
> that he has but since it is just 4-way, it is more powerful than an 8-way.
> I haven't received it yet but I should be able to try it out soon to see if
> it fixes my problem.
>
> In the mean time, I remembered that I was splitting the line with my other
> MyHD tuner card with what I thought was a high quality "gold plated" 5-900
> Mhz passive 2-way splitter.  I decided to remove the MyHD card from the
> equation and plug my the card in my Linux box (Dvico Fusion HDTV5) directly
> into the wall to see if it fixes the problem.  Initially I saw no change in
> the signal strength and I still could not tune the atsc channels I knew were
> on 543 Mhz.  After about 15 minutes, I tried azap again on that frequency
> and I was suddenly getting a signal lock on that frequency which I never got
> before.  It was locking but it still looked like it was just strong enough
> to get a unbroken lock on the frequency when I saw the signal strength as
> straight cxxx.  It was holding for a while so I was finally able to map all
> the channels with dvbscan that I could never do before.
>
> The next day it was still working but when I checked it again at the end
> of the day, it had reverted back to the old fluctuation in the signal
> despite removing the MyHD card and the splitter.  I have at times been able
> to lock onto it again and gotten a weak lock but not for long and as I write
> this, I am experiencing fluctuations on that frequency again and am unable
> to watch any of the channels on that frequency.
>
> I report my findings here again after I test the amp which will give me an
> 8db bump on the port.  If it fixes the problem with tuning that frequency on
> my Dvico card, I'll test the amp with my MyHD card to make sure that
> additional tuner cards don't exacerbate the problem with tuning on those
> frequencies.
>
>
>
> On 2/18/07, Matthew T. Russotto <mrussotto at speakeasy.net> wrote:
> >
> > Unfortunately, I don't think that's a driver bug but a hardware
> > limitation.  My PCHDTV 5500 card seems to be less sensitive to signal
> > or more sensitive to interference on CATV 76 and 77 (537 and 543 Mhz).
> > I was able to fix my problem by replacing a set of two-way splitters
> > with a higher-quality 3-way splitter and putting the problem card on
> > the 4db drop leg.  Having another card (a KWORLD ATSC 110) in the
> > system seems to exacerbate the problem.
> >
> > If there's a way to remedy the issue in software I'd expect it to be a
> > tuner parameter; are you also using a PCHDTV 5500 or other card with LG
> > tuner?
> >
> >
> > _______________________________________________
> > linux-dvb mailing list
> > linux-dvb at linuxtv.org
> > http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
> >
>
>
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