Pixelation when watching UK Freeview channels

[CyberSimian]

Checked signals - all tuners around 90 % strength and 89% quality. I recently had a new aerial fitted with a single cable running directly to the TBS-6284 - no splits, joins or other devices in between. I have an unobstructed line of sight to the transmitter according to the information on ukfree.tv.

The 89% quality looks slightly worrying (ought to be 100%), but I am not convinced that "ScanChannels" is returning an accurate figure.

I have one version of "ScanChannels" on my HTPC, and I tried running it this morning. For the primary transmitter serving my area (Rowridge), the results for a TBS 6284 tuner were similar to yours. For a secondary transmitter (Hannington, in the opposite direction), the results were much worse (as one would expect, since my aerial points at Rowridge). But I also have a pair of Pinnacle 2000i dual-tuner cards in my HTPC (not DVB-T2), and for those, "ScanChannels" showed 100% strength and 100% quality, for all MUXes from the primary transmitter; it was only for a MUX from the secondary transmitter that quality dropped to circa 80%.

For domestic equipment, one cannot compare signal strength measured by different devices (it is only a relative indication of signal strength), but I thought that signal quality was determinable precisely, and different devices ought to give the same figure for the same signal. Possibly the different results from the TBS and Pinnacle tuners is a driver issue, and who knows which is correct (possibly neither!). There was some talk a year or two ago that the TBS tuners did not return the correct signal strength/quality values for DVB-T2 MUXes; perhaps the values for DVB-T MUXes are bit suspect too.

-- from CyberSimian in the UK

[kitehigh]

If it is was a weak signal that would suggest that each tuner has some detrimental effect on the signal being passed through the card - because the more tuners active the worse the pixelation gets across all simultaneous recordings.

I will try running scanchannelsbda.exe on a tuner then starting/stopping recordings on the other 3 tuners and see if the strength or quality varies.

[CyberSimian]

Ok, so I tried recording 4 shows in NextPVR - making sure each was on a different MUX - and guess what: same pixelation problem as in WMC...

The TBS 6284 is a quad-tuner card that actually consists of two dual-tuner units on a single card. That is why there are two aerial input sockets on the card. How are these connected? Have you connected the output socket of one dual-tuner to the input socket of the other dual-tuner? If I remember correctly, TBS actually provide a very-short co-axial cable for this purpose, so it is tempting to use it. But I was not happy that the tuners would all receive the same signal, so I have separate feeds to the input sockets on my TBS 6284.

As I have a total of 8 tuners in my HTPC (4 DVB-T, and 4 DVB-T2; see my previous post), I have the following aerial setup:

(1) A loft aerial, about 30 miles from the primary transmitter (no metal foil in the roof lining).
(2) A single non-amplified feed from the loft to the lounge.
(3) A one-input/two-output aerial amplifier in the lounge, with one feed going to my Humax HDR-FOX-T2 PVR, and the other feed going to a one-input/four-output aerial amplifier.
(4) Two outputs from the four-output aerial amplifier going to the TBS card, and the other two outputs going to the two Pinnacle cards.

I have had this setup for several years, and used to get occasional pixelation on the weaker MUXes (especially when the atmospheric conditions were unfavourable, or when the central heating switched on or off). However, since analogue switch off, the signal strength has increased and I only rarely get pixelation, even on the weaker MUXes.

Although it is possible that you have one or more faulty tuners on your TBS 6284 card, at this juncture I would be inclined to think that your signal strength is too low for the multiple tuners, and would suggest trying an aerial amplifier. If the aerial feed goes only to your HTPC, get a one-input/two-output aerial amplifier, so that you can separately feed each input socket on the TBS 6284; leave the output sockets on the TBS 6284 unconnected. If you have other devices that you want to feed, get an aerial amplifier with more outputs.

In general, the recommendation is to place an aerial amplifier as near to the aerial as possible (e.g. a masthead amplifier or loft amplifier), but an amplifier in the lounge is still worth trying (and is what I use).

-- from CyberSimian in the UK

[milli260876]

PSU dying??

[milli260876]

I'd suggest a mast head amplifier to a splitter amp if you can take the sources seperate from your loft if you're looking at doing that.
FYI I can see my mast (emley moor) and still need an amp for HD if I use more than one tuner.

[kitehigh]

Hi, so been a while but once one problem was sorted another has manifested itself with channels randomly refusing to start altogether.. but this may be to do with xbmc tinkering so I'll not go into that here.. as for getting WMC itself running:

Progress was made with the addition of a splitter-amplifier as suggested - once a channel has started I now get perfect playback, recording or not

Now I just need to work out how to stop wmc making changes to the sources! Very frustrating and haven't found a solution that works yet (multiple transmitters visible and each with offsets - wmc never seems to get the right one!). Tried adding the PeriodicScanEnabled=0 entry and setting PeriodiScanIntervalSeconds=FFFFFFF - this just gets reset to the default value every so often so changing it makes no long term difference...

[CyberSimian]

Progress was made with the addition of a splitter-amplifier as suggested - once a channel has started I now get perfect playback, recording or not

Excellent!

Now I just need to work out how to stop WMC making changes to the sources! Very frustrating and haven't found a solution that works yet (multiple transmitters visible and each with offsets - WMC never seems to get the right one!). Tried adding the PeriodicScanEnabled=0 entry and setting PeriodiScanIntervalSeconds=FFFFFFF - this just gets reset to the default value every so often so changing it makes no long term difference...

There is another registry key that you may need to set to stop opportunistic scanning; see this thread:

http://www.thegreenbutton.tv/forums/vie ... f=28&t=698

It is not clear how this registry key interacts with the ones that you have already tried. I have set both and do not suffer from opportunistic scanning, but then I still use Vista; Win 7/8 may have different logic in this area.

If setting the additional registry key does not solve your problem, you could try using a notch filter in your aerial cable. A notch filter attenuates the signal, but over a very narrow range of frequencies (e.g. corresponding to a single MUX). Depending on where in the frequency band the unwanted MUXes are, this may or may not be a solution. Here is an example of a notch filter:

http://www.satcure.co.uk/tech/notch_filter.htm

-- from CyberSimian in the UK

[kitehigh]

Hi, thanks for the ongoing help!

I have applied the regedits as per that thread but to no avail.
Still wmc selects sources it shouldn't every few days... leading to tuning problems and missed recordings. Really getting old now.

I think the notch filter would be difficult to get right or I would need lots of them as my problem is over a number of muxes with the + and - offsets...

[CyberSimian]

I have applied the regedits as per that thread but to no avail. Still WMC selects sources it shouldn't every few days... leading to tuning problems and missed recordings.

If I recollect correctly, there have been other reports of people trying the registry fixes but finding that it does not solve their problem. It raises the question of whether these fixes have ever worked for Win7. They do work for Vista, but I doubt that you want to downgrade to Vista (not least because Vista cannot receive high-definition DVB-T2 broadcasts).

If anyone has tried these registry fixes on Win7 and found that it solves the problem, please post here to confirm that these fixes do (sometimes) work.

I think the notch filter would be difficult to get right or I would need lots of them as my problem is over a number of muxes with the + and - offsets...

The notch filter that I suggested can suppress two independent frequencies (i.e. two MUXes) and costs around £22. But I have never used one, so I do not know how effective it would be. Also, the unwanted MUXes need to be several UHF channels away from the wanted MUXes, because the notch filter will seriously attenuate the adjacent channels too. In my case it would work, because my highest wanted MUX it at UHF channel 31 (554MHz), and the unwanted MUX is at UHF channel 45 (666MHz).

If your unwanted MUXes are not intermingled with the wanted MUXes, an alternative to a notch filer would be a UHF bandpass filter that attenuates an entire band of frequencies (the satcure.co.uk website lists several, around £8-£10 each). That would also work for me -- I would buy a filter that passed UHF band A but which attenuated bands B, C, and D. The most that you would need would be two (e.g. if your wanted MUXes are in band B, buy one filter to attenuate band A, and another to attenuate bands C/D).

The only other possibility that might offer a solution is to fiddle with your aerial, and point it in slightly different directions. You may be able to find a direction that reduces significantly the signals from the unwanted transmitter, but does not reduce too much the signal from the wanted transmitter. But I note that your aerial installation is new, so you may not want to fiddle with it (especially if it is outside on a roof/chimney).

I agree that the correct solution is for the software not to rescan, but if there is no way of stopping that, the only solution seems to be to do something with the UHF signal (notch filter, bandpass filter, re-align aerial).

-- from CyberSimian in the UK

[holidayboy]

I definitely stopped opportunistic scanning by setting regedit values. I'll post the exact ones I set later, it's been a while.

[holidayboy]

Another option is to use DVBLink TVSource and let it do the scanning - it will only use the signals that you tell it to.

[kitehigh]

Another option is to use DVBLink TVSource and let it do the scanning - it will only use the signals that you tell it to.

This could work but costs money! And knowing my luck with all this would be something else to go wrong...

I definitely stopped opportunistic scanning by setting regedit values. I'll post the exact ones I set later, it's been a while.

That would be much appreciated

[holidayboy]

The reg keys that I set are the two that Cyber posted above:

http://www.thegreenbutton.tv/forums/vie ... 5850#p5850

I haven't seen the keys revert back as you seem to have seen.....

Maybe run regedit as administrator / set the keys to read only for all accounts (take a full backup of the registry first!)

[mercalia]

I find a few Freeview channels are the culprit - Pick is one. I also think some tuners maybe sensitive to particular channels. I have a Haupage and a Compro videomate E700 (I think it is ) The Compro seems to be more prone to pixelation that the Hauppage one. Just a guess, so I change the priority in the tuner list for that channel, place the Compro lower down in the list.