On Mon, 10 Jul 2006, Michael Krufky wrote: > Trent Piepho wrote: > > On Mon, 10 Jul 2006, Michael Krufky wrote: > >> 0x20 for analog, 0x50 for digital. > > > > Ahh, so there is code in the dvb version of the tuner driver that changes > > the AGC take-over point to a different value? I wonder if this should be > > done to the other ATSC/NTSC tuners with TAU603x chips, of which there are > > many. > > Name one other? (maybe there are more... i dunno) ... FYI, The Thomson DTT 7612, used in the HD-3000 card. It has a TUA6030 which also supports AGC take over point adjustment. I think a better question would be which ATSC/NTSC tuners _don't_ have a PLL with take over point adjustment? > One should NOT assume that the TUA6034 within the LG H06xF NIM is > handled in the same exact manner as within other devices. Quite true. The TUA603x datasheets are not very clear on what adjusting the AGC take over point actually does. It probably depends on a paticular tuner's construction, just like the band ranges. Anyway, I tested setting the AGC TOP to different values on my HD-3000. I tuned a 256-QAM channel and recorded SNR and signal level every second. Then I changed the TOP to all 7 supported values about every 30 seconds. Anyway, here is graph of the effect of the different TOP values: http://www.speakeasy.org/~xyzzy/agctop.png There appear to be two modes for AGC TOP setting. One is to set the IF output level to something between 103 and 115 dBuV (default 112). The other is to disable AGC and fix the I_agc current at 0 or 9 uA. Honestly, I don't totally understand this stuff. Anyone who does care to explain? If you look at the graph, the signal is clearly best at the lowest setting (103), and gets worse as they get higher. The two settings which have AGC disabled are much worse. It looks like the AGC TOP setting business for LG H06xF helps the ATSC tuning for the DTT 7612 too. Might well apply to nearly all ATSC/NTSC tuners. I also tried changing AGC TOP while watching analog channels. The settings with AGC off had some more noise in the picture. With AGC on I didn't notice any difference. Doesn't mean much though, my analog picture looks like crap, I'd never be able to notice 10% more noise with my eyes. > Hmm... Looks like you're right. We always set 0x50 during digital > tuning in lg_h06xf_pll_set, but it looks like 0x20 is only set during > tuner_set_type. Meanwhile both analog and digital modes are functioning It's actually probably never set to 0x20. Only if the high bit of the unitialized value of bufffer[2] happens to be set, will the code set AB to 0x20. If buffer[2] was 0 - 0x7f, it won't do anything. > > Still, a stop-gap fix can be made now. The tuner needs to program the AB > > either: > > 1) When the V4L device is opened > > 2) Every time the tuner is programmed > > For now, if it's not broken, don't fix it. Let's see what Mac says, first. It's obviously broken now. It's just that agc top in NTSC mode doesn't seem to matter much, so there isn't anything wrong that someone would notice. Does the LG datasheet say anything w.r.t. the agc top setting in NTSC mode? PS. Sure wish I could label SNR in dB instead of unknown mystery units. _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
