One TV channel is duff - all the others are OK (2 Viewers)

[Ralph Holmes]

I use MP2 on Windows 10 64-bit. I use a Hauppauge WinTV-dualHD USB device and a dedicated TV aerial for this PC.
I watch via terrestrial Freeview on the UK's Taclesneston transmitter.
"Talking Pictures TV" gives a very poor quality of picture and audio. All the other channels are fine. "Talking Pictures TV" works as well as any other channel on my TV set.
This is the tuning detail for this channel.

Is there any way in which I can ameliorate the quality of this channel, please? Keep it simple, please.

 

[CyberSimian]

"Talking Pictures TV" gives a very poor quality of picture and audio. All the other channels are fine.

By "other channels" do you mean "other channels in the MUX that contains Talking Pictures", or do you mean "the channels in other MUXes"?

In this post I have attached a zip file containing the tool ScanChannelsBDA_UK.exe. If you invoke it from the command line, it will scan all possible frequencies and display the channels in each MUX and the signal strength of each MUX. It might indicate that the MUX containing Talking Pictures is much lower signal strength than the other MUXes. If the signal strength looks OK, it will tell you what other channels are in that MUX, so you can view those channels to see if they are as bad as Talking Pictures.

I have got Talking Pictures on now, and the video and audio seems OK to me (Rowridge transmitter).

-- from CyberSimian in the UK

 

[Ralph Holmes]

Thank you for replying so rapidly.
MUX ? I'm guessing something to do with multiplexing, but an internet search gives too many options to explore easily.
The group containing Talking Pictures TV has signal strength = 35, Signal quality 4%.
Other groups have signal strength = 40+, signal quality = 60%+
The results are similar with either of the twin tuners.
The other channels in the Talking Pictures TV are channels I never look at: however, attempting to preview them shows that none of them is giving a viable signal.
Is there anything I can do?

 

[CyberSimian]

The group containing Talking Pictures TV has signal strength = 35, Signal quality 4%.
Other groups have signal strength = 40+, signal quality = 60%+

It is not immediately obvious what is causing this problem, or how to cure it, but here are some possibilities:

(1) There was a "retune event" in the UK recently, caused by some re-arrangement of channels, MUXes, and frequencies in some regions. You should perform a channel scan in "TV Server Config" if you have not done this within the last few days. Remember to select the Enable channel movement detection setting.

Modern TVs automatically rescan when changes occur, but MP's "TV Server" does not.

(2) If your HTPC receives its signal from the same aerial as your TV, unplug and replug all of the co-axial cables. Sometimes oxidation can build up on the plugs, reducing the signal. Unplugging and replugging should clear some/most of the oxidation.

(3) Check cable routing, and ensure that the co-axial cable does not run close to and parallel to an HDMI cable. A poorly-made HDMI cable can radiate signals that can interfere with the TV signals (but not at all frequencies). If the cables must cross, try to ensure that they cross at 90 degrees. Also, perhaps try a different HDMI cable, or a different co-axial cable.

(4) If your HTPC receives the signal from a separate aerial, try swapping the aerial connections between the HTPC and TV (so that the HTPC receives the signal from the TV's aerial).

(5) If the Talking Pictures MUX has moved to a higher frequency, it is possible that your aerial is no longer suitable. Aerials have physical dimensions that are optimised for a particular range of frequencies, classified by letters: group A, group B, group C, group D, and the now defunct group E. There is also a wideband group called group W.

Group A aerials are optimised for lower frequencies, and will have poor response at higher freuencies. 618MHz is on the high side. I use a group A aerial, but my highest frequency is 530MHz. If the Talking Pictures MUX has moved to a higher frequency, you may now have a mismatch between the aerial group and the frequencies you are trying to receive.

There is no simple way of checking this. It probably requires employing an aerial installer to replace your existing aerial (cost: perhaps £250?). So you don't want to do this unless you have exhausted all other possibilities.

(6) Tuners in HTPCs are less sensitive than tuners in TVs, so your HTPC may simply be too insensitive to receive a weak signal at adequate quality, whereas your TV has no problem with it. If this is the case, you will either need a better aerial, or accept that you cannot watch or record Talking Pictures on the HTPC.

-- from CyberSimian in the UK

 

[Ralph Holmes]

Thank you for your reply - I'm working through the list.
It crossed my mind that the absence of signal at on frequency suggested some sort of filter. I have an amplifier between the aerial and the tuner: having removed the amplifier gives a much improved signal for the group containing "Talking Pictures TV", so this may have caused the problem. However, I would not have detected this without the ScanChannelsBDA_UK.exe tool, so thank you again for providing that.
Other frequencies have a slightly reduced signal strength as a result of this action, but the signal quality does not appear to have suffered.
Cheers
Ralph

 

[CyberSimian]

having removed the amplifier gives a much improved signal for the group containing "Talking Pictures TV"

That is an interesting an unexpected result.

Aerial amplifiers are optimised for a specific range of frequencies (just like aerials), but amplifiers usually cover the entire UHF band, from about 270MHz to 850MHz. With the removal of the amplifier, the reduction in the signal strength for the other MUXes is expected, but the improvement in the signal strength for the Talking Pictures MUX is unexpected, so there may be some other factor involved.

Possibly it was just oxidation on the plug and socket contacts, or the physical routing of the cables, and it will all work correctly again when you reconnect the amplifier. But if the problem persists, it would be worth trying a different aerial amplifier, if you have one available.

-- from CyberSimian in the UK

 

[Ralph Holmes]

Interesting, unexpected and wrong!
As you indicated, the co-axial onnectors were at fault.
Nevertheless, your helpfulness has inspired me to get to grips with the problem, so, thank you very much again.

Cheers

Ralph