Em 15-03-2012 14:49, Antti Palosaari escreveu: > On 15.03.2012 19:41, Mauro Carvalho Chehab wrote: >> Em 15-03-2012 14:33, Gianluca Gennari escreveu: >>> The PCTV 290e had several issues on my mipsel-based STB (powered by a >>> Broadcom 7405 SoC), running a Linux 3.1 kernel and the Enigma2 OS. >>> >>> The most annoying one was that the 290e was able to tune the lone DVB-T2 >>> frequency existing in my area, but was not able to tune any DVB-T channel. >>> >>> Following a suggestion of the original author of the driver, I tried to >>> tweak the wait time in the lock loop. In fact, increasing the wait time >>> from 50 to 200ms in the tuning loop was enough to get the lock on most >>> channels. >>> But channel change was quite slow and sometimes, doing an automatic scan, >>> some frequency was not locked. >>> So instead of playing with the timings I changed the behavior of the >>> search algorithm as explained in the patch 1, with very good results. >>> >>> With this modification, the automatic scan is 100% reliable and zapping >>> is quite fast (on the STB). There is no noticeable difference when using >>> Kaffeine on the PC. >>> >>> But there was a further issue: a few weak channels were affected by high >>> BER and badly corrupted pictures. The same channels were working fine on >>> an Avermedia A867 stick (as well as other sticks). >>> >>> The driver has an option to enable a "Low Noise Amplifier" (LNA) before the >>> demodulator. Enabling it, the reception of weak channels improved a lot, >>> as reported in the description of patch 2. >> >> Hi Gianluca, >> >> With regards to LNA, the better is to add a DVBv5 property for it. >> >> The LNA is generally located at the antenna, and not at the device. > > LNA inside antenna, or near antenna, is called amplifier. Power to that amplifier is feed by device or power supply using antenna cable. > > I see LNA more likely amplifier that is inside device. It could be external chip between tuner IC and antenna connector or more usually logical part inside tuner IC. > > Thus I see two different use cases here. 1) LNA, 2) power supply to amplifier. Yes, there are those two types of amplifiers. Some vendors ship hardware with a power amplify inside their antenna, and call it as LNA (as it is a low noise amplifier). >> As you know, more than one device may be connected to the same antenna, >> and it is generally not a good idea to have two devices sending power to >> the LNA. >> >> So, it is better to have a way to turn it on via the usespace API. >> >> Also, as this consumes power, the better is to do it only when the device >> is actually used. > > I think we need API support for LNA/amp + internal API support for AUTO LNA. Yes. > Originally I added LNA support as a module param for em28xx-dvb but Mauro NACKed it thus it is hard coded. Anyhow, some method switching LNA on/off is better than no method at all Well, adding one or two DVBv5 properties to enable/disable the LNA is very easy. So, instead of adding hacks, let's just do the right thing. > > regards > Antti > Regards, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
