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can not watch DVB-C -- switch LNA on/off for dvb-c ?

Added by Daniel D over 4 years ago

Dear tvheadend experts,

I have a Geniatech MyGica T230C usb DVB-T/T2/C tuner stick and it works well on windows 7 x64, I can watch both dvb-t and dvb-c channels. With an android tablet using the padtv hd app I can watch dvb-t channels.
On linux ( latest Ubuntu with kernel 5.x ) I can only watch dvb-t channels.
The stick can tune the dvb-c channels but when selected a channel to watch there is no video or audio. There are some audio noises and sometimes some pictures with color rectangles but it seems not working. What can be the problem? Can be the signal level too high?

On the tvheadend config tab I can see the LNA checkbox only for dvb-t but not for dvb-c. Why?
Does the windows driver or the windows tv player application switch off the LNA (preamp) or sets a different (lower) amp rate to get things working? I suppose the windows driver contains the same fw like these in linux (see the log msg below).

thanks for any info
Daniel

Tvheadend 4.2.9
Linux: 5.3.0-46-generic (Ubuntu 19.10 64bit, Intel Core i3-6100, Intel HD graphics 530)
driver: dvb_usb_dvbsky
fw: dvb-demod-si2168-d60-01.fw version: D 6.0.2
fw: dvb-tuner-si2141-a10-01.fw version: 1.1.10

modinfo si2168 :

filename: /lib/modules/5.3.0-46-generic/kernel/drivers/media/dvb-frontends/si2168.ko
descr: Silicon Labs Si2168 DVB-T/T2/C demodulator driver

a channel tried for example:
590 0000 kHz bandwidth 8
6900 bauds
256-qam

channel scan in Kaffeine:
signal about 82.80 dBuV
SNR between 32 and 36.50 dB

perfect reception with dvb-t :
dvb-fe-tool --femon
signal= -52,00 .. -53,00 dBm C/N= 23,00 .. 24,00dB

no picture, no sound with dvb-c :
signal= -34,00dBm C/N= 37,50dB


Replies (11)

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by saen acro over 4 years ago

I never seen any DVB-C Low Noise Amplifier (LNA) on any device

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

thanks for info.
if this issue is not LNA related should I check fw files? am I right fw files used in linux (eg. by libreelec) are extracted from the official windows driver installer?

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

Maybe I should change some parameters on the tvh configuration / dvb inputs / tv adapters / dvb-c / Parameters screen? Maybe different default values are used on linux as on windows?

tvh_rpi3_le9_2_0.jpg (135 KB) tvh_rpi3_le9_2_0.jpg tvh running on rpi3 libreelec 9.2.0 + windows media player
tvh_rpi3_le9_2_0_vlc_codec.jpg (133 KB) tvh_rpi3_le9_2_0_vlc_codec.jpg tvh on rpi + vlc on win
tvh_rpi3_le9_2_0_vlc_stats.jpg (68.6 KB) tvh_rpi3_le9_2_0_vlc_stats.jpg tvh on rpi + vlc on win
tvh_settings.jpg (148 KB) tvh_settings.jpg tvh dvb-c conf

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by saen acro over 4 years ago

This is demonstration when signal is bad and maby there is a BER.

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

Using the same tuner stick and same dvb-c cable signal on windows plays the same channel perfectly.
Thats why I think there is some difference between the linux setup and the windows setup.
How could I determine in which layer is the difference? Firmware? Dvb driver? Using (init, setting params, stream the channel content) the driver?

samesignalusedonwin.jpg (86.4 KB) samesignalusedonwin.jpg same cable signal perfect on windows
samesignalusedonwin_freq_ok.jpg (108 KB) samesignalusedonwin_freq_ok.jpg freq stats on win

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by saen acro over 4 years ago

Diver under Linux is not 100% same as on Windows.
Signal levels measurement.

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

Could be a driver issue? Should I make a ticket at the driver repo?

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by saen acro over 4 years ago

Daniel D wrote:

Could be a driver issue? Should I make a ticket at the driver repo?

Mainly on RPI dev's this mobo is worst then you thing

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

I tried with all of the three dvb drivers selectable in libreelec on rpi3 (kernel 4.xx) and tvheadend.
I tried also on ubuntu (latest 5.xx kernel) with the default kernel driver and vlc (without using tvheadend).
All of them failed to play the content correctly.

tvh_with_le_tbs_drivers.jpg (63.4 KB) tvh_with_le_tbs_drivers.jpg libreelec
ubuntu_vlc.jpg (266 KB) ubuntu_vlc.jpg
ubuntu_femon_vlc.jpg (106 KB) ubuntu_femon_vlc.jpg

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by saen acro over 4 years ago

You have BER etc signal is not good.

RE: can not watch DVB-C -- switch LNA on/off for dvb-c ? - Added by Daniel D over 4 years ago

I tried with an attenuator to lower the input signal but still no luck. It seems to me the signal has no problems at all.
There are different firmware files for this stick at osmc repo, at librelec and at coreelec repos (same name, different sizes). I suppose I should ask the developers commited these how they produced the files and what windows driver version (s)they used....
On windows and on my flat screen television I can watch the channels.

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