[mythtv-users] : Re: Artifacts [solved]

John Pilkington johnpilk222 at gmail.com
Sun Dec 23 16:11:38 UTC 2018

On 23/12/2018 13:23, jam at tigger.ws wrote:
>> On 23 Dec 2018, at 6:41 pm, mythtv-users-request at mythtv.org wrote:
>>> Hi
>>> because some of our channels have been playing games with their names I dropped all channels and rescanned.
>>> All good EXCEPT many channels, specially HD channels, are plagued with artifacts and chirps and squeeks typical of poor signal quality.
>>> I checked frequency in sql table channelscan_dtv_multiplex and they are identical.
>>> I restored old db with mythconverg_restore.pl and problem is totally gone.
>>> What can I say or not say to the db that will affect tuning. The stations are correct just apparant signal strength is bad.
>>> I stress NO hardware or software changes or conections are changed in any way ONLY mythconverg DB changes.
>>> Whatcould be happening?
>>> James
>> Was the old table created with the same tuner - its possible that a
>> field set previously to auto might need a parameter. The easiest check
>> is compare all the old and new tuning parameters.
> Interedting and may well be of interest:
> I live equidistant-ish to 3 transmitters and in range of another two
> Perth - Willetton https://www.txaustralia.com.au/tvcoverage
> Each scan is different. Trick was to scan (say) 5 times add the results and delete not-good channels.
> One transmitter site did not yield best results on every channel!
> So a chance good scan once upon a time, was just luck.
> James
> PS a note to any developers who may be bored :-)
> 1) it would be nice to be able to see signal-strengths a la scanning to easily select WHICH channels to prune
> 2) It would be nice to be able to edit channel frequencies and match frequencies to channels eg
> scan choose a frequency of 663. 250000 instead  of 663 500000
> sql fiddling to get a list of frequency vs chan

Perhaps a more directive antenna would be a good investment?  And maybe 
one of the freestanding scan programs would give signal strength info.

I get this sort of output at the end of a mythtv-setup scan - and 
usually a 'rescan existing transports is OK, unless some 
spectrum-management has been happening.  It shows modulation type, 
transport freq, channel name, channel number, transmitter ident, country 
ident and dvb parameters.

Now you know which transports you want.  Make a note of them and perhaps 
delete the others?


2018-10-25 12:35:26.588671 I  Current MythTV Schema Version 
(DBSchemaVer): 1348

qam_64:538000000:5 USA:21:12323:9018:12992:12294=12294:dvb 

qam_64:698000000:BBC ONE E Mid:1:12323:9018:4166:4166=4166:dvb 
qam_64:698000000:BBC TWO:2:12323:9018:4287:4166=4166:dvb 


qam_64:602000000:Sky News:233:12323:9018:22080:20544=20544:dvb 


qpsk:514000000:Notts TV:7:12323:9018:32844:32780=32780:dvb 
qpsk:514000000:POP Max:208:12323:9018:33280:32780=32780:dvb 

Found 7 transports:   --------->  I can only see 6 here :-)
Channels: FTA Enc Dec
ATSC        0   0   0
DVB       142   0   0
SCTE        1   0   0
MPEG        0   0   0
NTSC        0
Unique: prog 143 atsc 0 atsc minor 0 channum 143
Max atsc major count: 0




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