HD channel break up (SD okay)

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HD channel break up (SD okay)

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unloveablesteve

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Hi

Just had terrestrial aerial fitted in loft space. Unfortunately, I wasn't about when it was put in so unsure of make/type and whether or not a booster was added to circuit. TV loops in master bedroom (2nd floor) straight into Panasonic TV with internal freeview, no problems (although not all HD channels being found on most recent scan).

However, Humax HDR FOX T2 (1st floor) connected to Panasonic HD ready telly is breaking up on the HD channels. I've read around the forums and thought maybe it was signal strength (seems to be around 100% strength to 60% quality on each mux) but am baffled about why SD would be fine and HD breaking up/pixellating so badly. If I try an attenuator to bump down the strength on the HD mux, am I risking losing the SD mux?

FYI, we're 44km from Crystal Palace (in Ware, Herts), and I've done both manual and automatic tuning.

Cheerio

Steve

| Tue 9 Apr 2013 13:57:03 #1 |
Martin Liddle

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unloveablesteve - 4 minutes ago »
However, Humax HDR FOX T2 (1st floor) connected to Panasonic HD ready telly is breaking up on the HD channels. I've read around the forums and thought maybe it was signal strength (seems to be around 100% strength to 60% quality on each mux)

100% strength is way too high. It sounds as though there is an amplifier in the circuit and it is over amplifying the signal and saturating the Humax tuner. Talk to the installer and see if the amplifier gain is variable and if so turn it down. If not the options are to try without the amplifier or to fit an attenuator in the aerial cabling to bring the signal level down. I would aim for a signal strength on the Humax between 50% and 90%.

| Tue 9 Apr 2013 14:05:37 #2 |
unloveablesteve

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Thanks, Martin.

I've checked with the installing engineer. There is indeed an amplified splitter adding 8dB to the signal in the loft with the aerial. I don't think it's variable (I've asked them to get back to me about that). I might pop in to Maplin on the way home an pick up a couple of 6dB attenuators.

How would it be that the signal strength is only negatively affecting the HD mux, by the way?

Cheerio

Steve

| Tue 9 Apr 2013 15:05:30 #3 |
Martin Liddle

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unloveablesteve - 56 minutes ago »
How would it be that the signal strength is only negatively affecting the HD mux, by the way?

I wish I knew the answer to this sort of question. There is something about the Humax tuners that seems to make them more susceptible to various sorts of aerial problems than a lot of other kit.

| Tue 9 Apr 2013 16:03:57 #4 |
Watt Tyler

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unloveablesteve - 6 hours ago »

How would it be that the signal strength is only negatively affecting the HD mux, by the way?
Cheerio
Steve

I have heard it claimed that some HDMI cables can generate noise which affects the HD tuner. It might be worth checking that by temporarily replacing the HDMI cable with a SCART. [Not a permanent solution because you won't get the benefits of HD with SCART, but you can at least see whether it makes a difference]

If it is better with a SCART, put the HDMI cable back and move it around while looking at signal strength and (particularly) quality on the Signal Detection menu, and see whether there's a position which improves the quality.

Signal quality is far more important than strength, and I'm a bit worried that you've only got 60%. I'm pretty sure that the Humax manual recommends making sure that the quality is at least 70% for reliable viewing. Mine is now a solid 100% on all muxes now that I've taken my trusty 30-year-old distribution amplifier out of the circuit - but that's a very long story (which you can read in another forum if you've got about 3 weeks to spare).

Suffice to say that amplifiers can introduce some sort of noise which the Humax tuner doesn't like, but which doesn't affect a TV sharing the same aerial feed and connected to the Humax's RF-out socket.

So, if playing with the HDMI cable doesn't achieve anything, try to get an un-amplified aerial signal to the Humax, and see what happens.

| Tue 9 Apr 2013 21:25:03 #5 |
unloveablesteve

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Hi Watt (how are the peasants? Still revolting?)

Thank you for the advice. I will give that a try at the weekend.

Firstly a couple of corrections to my own ham-fisted errata. My signal STRENGTH is at 60-70% and the QUALITY is around 100% on all muxes. The weird observation with the HD mux is that the quality bar flickers (on the tuning screen) between 100% and 0%, back and forth every now and again. I'm presuming that's what noise looks like.

The 6dB attenuator I tried last night didn't work, so I'm going to try again with a variable attenuator and punch it up to 20dB, then work down. If that fails, I will try the HDMI workaround instead.

Another factor I forgot to include is my Onkyo amp, which is taking the signal from the Humax (HDMI) and then taking it to the Panasonic (again via HDMI). Presumably this could also be adding noise or affecting the picture?

Cheerio

Steve

| Wed 10 Apr 2013 12:44:53 #6 |
Martin Liddle

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unloveablesteve - 1 hour ago »
My signal STRENGTH is at 60-70% and the QUALITY is around 100% on all muxes. The weird observation with the HD mux is that the quality bar flickers (on the tuning screen) between 100% and 0%, back and forth every now and again. I'm presuming that's what noise looks like.

OK so that is a reasonable signal strength; I don't think attenuators will help. I agree this looks like noise and if it isn't the HDMI lead then the prime candidate would be the amplifier. I would get the aerial installer back to look at the problem.

Another factor I forgot to include is my Onkyo amp, which is taking the signal from the Humax (HDMI) and then taking it to the Panasonic (again via HDMI). Presumably this could also be adding noise or affecting the picture?

I doubt it.

| Wed 10 Apr 2013 13:49:17 #7 |
Watt Tyler

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unloveablesteve - 4 hours ago »
Hi Watt (how are the peasants? Still revolting?)

Very much so! And, as their president, I should know! You won't find a more revolting peasant than me.

Thank you for the advice. I will give that a try at the weekend.
Firstly a couple of corrections to my own ham-fisted errata. My signal STRENGTH is at 60-70% and the QUALITY is around 100% on all muxes. The weird observation with the HD mux is that the quality bar flickers (on the tuning screen) between 100% and 0%, back and forth every now and again. I'm presuming that's what noise looks like.
The 6dB attenuator I tried last night didn't work, so I'm going to try again with a variable attenuator and punch it up to 20dB, then work down. If that fails, I will try the HDMI workaround instead.
Another factor I forgot to include is my Onkyo amp, which is taking the signal from the Humax (HDMI) and then taking it to the Panasonic (again via HDMI). Presumably this could also be adding noise or affecting the picture?
Cheerio
Steve

When my picture was breaking up (and that was on a couple of SD muxes - the HD one was more or less ok) the Quality bar on the Signal Detection screen would 'tombone' right and left, from 100% down to about 30%.

It does seem that that the Humax tuner is susceptible to certain types of noise which don't seem to worry TV tuners - and you're somehow going to have to find and eliminate the source of that noise. I don't know whether someone with an oscilloscope of high enough bandwidth would be able to see the noise on the aerial signal if they knew what they were looking for.

| Wed 10 Apr 2013 17:47:04 #8 |
Owen Smith

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At 60 to 70% signal strength you have enough strength to remove the amplifier I would suggest. This may need replacing with a passive splitter but as a test you could simply bypass it on the leg that goes to the Humax ie. connect input to output if you know what you're doing.

You could also try simply turning off the mains feed to the amplifier, some of them become pass through without power. Other amps become a total block without power though, so depending on your amp this may or may not work.

After that I'd start asking questions about screening on the coax drops and the splitters etc. The splitters and amps should all be fully screened for Freeview, and the coax should be CT100 double screened where one of the screens is a continuous foil screen. Without this you can pick up impulse interference on the cabling. The other way to combat that is to increase the signal strenght ie. more amplification to get to nearly 100% strength, this increases the level of the signal compared to the picked up noise on the cable. Then you can stick 10db attenuation in the back of the Humax, this reduces the signal strength back down but also reduces the noise that was picked up on the cable.

The goal always is to have sufficiently more signal than noise by the time it gets into the Humax. There are several different ways to approach that.

| Sat 13 Apr 2013 20:13:43 #9 |
unloveablesteve

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Hi all

Thank you for all your help. Here's the weird thing.

Nothing I tried worked. Attenuator up to 20dB had no effect. Switching off the amplifier had no effect. Running through SCART instead of HDMI had no effect.

Then, on Thursday, we had our phone line and broadband installed (Sky fibre, if you're interested, courtesy of a BT Openreach engineer). Since then, the HD channels have worked. Not brilliantly, not 100% of the time, but solidly enough to record programmes off with virtually no signal break-up.

Again, I wasn't around when the engineer sorted out the phone line, but I gather he didn't even play around with the main media panel in the living room (just the downstairs main phone socket). I'm sure it's entirely possible that *not* having a phone line could've caused noise on the Humax HD, but it seems odd. Alternatively, it could just be coincidence that the box "fixed itself" at the same time as our broadband appeared.

*Clueless!*

Any suggestions/diagnosis/theories here gratefully received.

Cheerio

Steve

| Sun 21 Apr 2013 22:37:36 #10 |