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

Matthew Schultz mattsch at gmail.com
Mon Feb 19 06:37:42 CET 2007

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

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?
> _______________________________________________
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> linux-dvb at linuxtv.org
> http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
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