[linux-dvb] Nova-TD Stick too sensitive?

Jonas Anden jonas at anden.nu
Wed Dec 12 23:24:35 CET 2007


I have a strange problem with my Nova-TD Stick (USB ID 2040:9580).

A couple of months ago, I rebuilt my antenna setup and replaced all the
cables, the amplifier and splitter by high-quality versions, and since
then all the other cards (one Nova-T 500 and one Nova-T Stick) have
gotten much improved signal quality. But for some reason, the Nova-TD
Stick won't lock. MythTV claims 100% signal strength but doesn't achieve
a lock. Since I really don't *need* the TD tuners (I got the TD before I
got the "simple" T stick and before there was any hint of any Linux
drivers for it, and three tuners really "ought to be enough for
anybody[tm]"), I was content with leaving the TD stick unconnected. 

Yesterday, however, my system crashed again (due to i2c errors), and I
went to work updating the box to the latest (F7) kernel, updated the hg
tree and recompiled all the dvb drivers (haven't seen any i2c errors
since then, btw -- Yay!). Just for the fun of it, I plugged in the TD
stick to see if the situation had improved. It hadn't. I tested using
the MythTV suggestions; use tzap -r to set it to streaming, and cat >
video.mpg. tzap claims it gets a lock, but I receive no data from the
stick. The tzap output looks like this:

# tzap -r -a 4 'TV6'
using '/dev/dvb/adapter4/frontend0' and '/dev/dvb/adapter4/demux0'
tuning to 642000000 Hz
video pid 0x0437, audio pid 0x0436
status 0a | signal ffff | snr 0000 | ber 001fffff | unc 00000000 | 
status 1a | signal ffff | snr 0000 | ber 001fffff | unc 00000000 | FE_HAS_LOCK
status 1a | signal ffff | snr 0000 | ber 001fffff | unc 00000000 | FE_HAS_LOCK
status 1a | signal ffff | snr 0000 | ber 001fffff | unc 00000000 | FE_HAS_LOCK
status 1a | signal ffff | snr 0000 | ber 001fffff | unc 00000000 | FE_HAS_LOCK

Being a bit careless, I accidentally left the cat and tzap running while
unplugging the device from the amplifier. Lo and behold, the signal
level dropped, and it started feeding data into the mpg file. Only
temporarily while the cable was aimed in the "wrong" direction, but yet
-- the dvr0 device actually generated data! Once I completely
disconnected the signal cable, the signal dropped down to 0 (pretty much
expected):

# tzap -r -a 4 'TV6'
using '/dev/dvb/adapter4/frontend0' and '/dev/dvb/adapter4/demux0'
tuning to 642000000 Hz
video pid 0x0437, audio pid 0x0436
status 00 | signal 0000 | snr 0000 | ber 001fffff | unc 00000000 | 
status 00 | signal 0000 | snr 0000 | ber 001fffff | unc 00000000 | 
status 00 | signal 0000 | snr 0000 | ber 001fffff | unc 00000000 | 
status 00 | signal 0000 | snr 0000 | ber 001fffff | unc 00000000 | 
status 00 | signal 0000 | snr 0000 | ber 001fffff | unc 00000000 | 

Interesting, I thought. So I dug out the little "mobile" antenna that
comes with the stick. I didn't expect to get anything working, but with
that antenna I *do* get a lock even though the signal strength and
quality for that is *much* worse than through the active antenna and
high-quality amplifier. MythTV can tune, claiming ~20-40% signal quality
(depending on which multiplex I tune to). The picture works just fine,
and tzap is displaying something in between the two outputs above:

# tzap -r -a 4 'TV6'
using '/dev/dvb/adapter4/frontend0' and '/dev/dvb/adapter4/demux0'
tuning to 642000000 Hz
video pid 0x0437, audio pid 0x0436
status 07 | signal 6343 | snr 0000 | ber 001fffff | unc 00000046 | 
status 1f | signal 634f | snr 0000 | ber 000002b0 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 634b | snr 0000 | ber 00000220 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 6358 | snr 0000 | ber 00000290 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 634e | snr 0000 | ber 00000420 | unc 00000000 | FE_HAS_LOCK

Conclusion: The Nova-TD stick doesn't like when the signal is too
strong. Is there anything in the driver code that makes this happen?

I'm thinking perhaps noone ever thought of receiving a 'ffff' value for
the signal strength and use that as a kind of error signal? Stranger
things have happened... ;)

Antenna        Signal   Data feed
-------        ------   ---------
None           0%       No data
Passive        38%      Data
Active         100%     No data
Active + Amp   100%     No data

Does anybody have any idea of how to get the TD stick operational with
its antennas fed from a strong signal? I've tried everything I could
think of...

  // J




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