Video recorder pixelated, TV is fine?

[Skylark NW]

A bit of background. About a year ago, I had a problem with both TV and video recorder screen pixelation after some changes at Winter Hill, north Manchester. It was solved by the nice people at Freeview by replacing my aerial. TV is LG, video is Samsung, both more than 10 years old.

Now, TV reception is fine but we still have occasional pixelation problems when viewing and recording through the video. The main aerial coax is first fed into the video, then out to the TV.

It's as though the receiver within the video is no longer as sensitive as the TV receiver, if that's possible. I've re-tuned the video several times but it's made no difference.

I'd appreciate any opinions and/or advice. Many thanks in advance.

 

[Lucid]

Different sensitivities between Freeview tuners is definitely a thing. Also, electronics drifting out of specification is a possibility too.

There are some other possibilities. As unlikely as it may sound, outdoor aerials (if that's what you have) can move over time. This would then change the signal level going to each tuner. Another possibility is that a switch mode power supply is becoming noisy, and that noise is being picked up via poorly-shielded coax and so reducing the signal.to.noise ratio which is part of what's displayed as the Quality measure.

All the above are about signals getting weaker or noisier. However, signals can also become stronger.

Our last tuning event was in Aug 2020. Depending on the aerial installed, there's always the possibility of signals moving in or out of higher or lower sensitivity regions for the aerial reception.

I have also come across one case where an aerial.amp with adjustable gain had rhe power tuned up. This creates a very similar effect to poor signal. Too much gain and the signal will pixelate and freeze too.

Tree growth and leaf loss can vary the signal.level being received too.

The first course of action is to ensure that sources of signal noise such as poorly shielded coax fly leads are replaced. Most leads manufacturered with moulded plug ends are poor quality. Replace them with good quality coax such as Webro WF100.

Next, have a look at the Quality and Strength readings for the recorder. These are normally given as info when completing manual tuning. Where you find that Strength is high but Quality is low then that suggests too much amplification in the aerial system. 70-100% for Quality, and just 50% on Strength is sufficient for perfect reception in many cases.

 

[Skylark NW]

Many thanks, Lucid,
The (new) aerial does not look to have moved since it was installed last summer. There is no aerial amp and both coax leads, from wall socket to video and from video to TV, look ok, albeit not changed in more than 10 years.
The problem last year was with BBC channels. The new aerial fixed it. More recently, we now have the problem on non-BBC channels.
Trees are a problem as there are a few mature and overgrown ones fairly close and in the firing line. The council has said that it will trim those overhanging into our garden.....but not given a date. That said, they have been like this for the 35 years that we've lived at the house. In windy and wet conditions we do get pixelation on any channel, in calm weather conditions I don't think they are a problem. The current issue seems to be that the video receiver is not as sensitive as it once was.
I've re-tuned per your suggestion. The Samsung only has two bar graphs, one shows "progress" and the other "signal status". The signal status shows about 2/3 on the bar graph. After re-tuning, comparing the same channel on TV and recorder, the TV is fine but there is occasional pixelation viewing through the recorder.
Any other suggestions would be much appreciated.

 

[mattylad]

Luckily for you, Lucid is not a really young chap but an experienced & knowledgeable one (that's sweet talk for he's older).
The young ones will simply say "What's a video recorder?"

 

[Lucid]

What model is the Samsung recorder?

 

[Skylark NW]

It's an SH893M.
I had a web chat with a Samsung agent yesterday. At first he suggested an aerial/reception issue but when I asked why the TV gave a good picture on the same channel, especially given that it receives its signal downstream of the recorder. His response was to suggest that I contact an authorised repairer.
I'd really like to get to the bottom of the issue. If the recorder is dying, I have no problem buying something to replace it. That said, I'd be pretty unhappy buying something new only to find that it doesn't work because there is a (marginal?) signal issue or later discovering that trees are the problem.
I appreciate you taking an interest, Lucid, thank you.

 

[Lucid]

Thanks for the model number. I had a quick squint at the manual. It doesn't look like there's any sort of Quality and Strength metering hidden away; just the progress bar as you said.

If I was on site then one of the first tests I'd do would be to measure the signal levels coming off the aerial wall socket for each mux. That would tell me how much margin you have to play with before the signal becomes marginal. Typical min/max levels are 45-65dB. In reality this still allows some safety margins. Many TVs will work fairly happily with 40dB up to 70dB of signal level so long as the SNR is healthy.

After checking the level at the wall socket, I'd then check the condition of the coax fly leads. If you're using those moulded ones, they can look okay externally, but inside they can hide broken solder joints and poor shielding. They'll still appear to work but they'll reduce Signal level and Quality (SNR). If you have a multi-meter and know how to do a continuity test then you can test the centre pin and the shield continuity for yourself.

It's worth noting too that the moulded cables tend to act as if they're lossier than good quality coax even when they're working correctly. I'm not a fan of them. They pick up interference far too easily and are often poorly constructed. I've been to troubleshoot installations where simply replacing one fixed most of the issues. In Autumn last year I helped a guy from N. Edinburgh diagnose his aerial issues. I recommended changing his coax fly lead. He couldn't find a local aerial shop to make one for him due to lock down. I posted one up, and he reported back that not only had it sorted the issue but he now got a higher number of channels on a channel scan. He then bought a second one from me for another TV. It's odd to thing of a 2m bit of wire making that much difference, but it just goes to show how poor the moulded cables can be.

Depending on the signal level measurements, if I got a low reading then I'd then do a stress test with the recorder to assess what sort of signal level margin it can work with on the main mux(es) where there's a problem. In your case that's RF channel 34 (578MHz, DVB-T) for PSB2 which is the main ITV / Ch4 / Ch5 SD mux.

Doing a stress test simply involves reducing the signal level to the point where the picture breaks up. This can be done with fixed-level in-line attenuators. I would recommend buying three values 3dB, 6dB, 9dB which will give a total range of 3~18dB when combined. If your signal is already marginal then as little as 3dB might be enough to tip things over the edge for the recorder.

I would then repeat the test but for the TV fed directly (recorder not inline). If you find you can get to 12~15dB of attenuation with the TV then you know that the recorder's tuner is on the way out. The problem with the recorder could simply be some poor capacitors that have had their chips.

Where the measured signal is high, I might suspect signal overload for that frequency. In this case I'd leave a 3dB attenuator in place or use a 1:2-way splitter which has the effect of reducing the signal level by 3.5dB


These aren't the only solutions. It's possible you have a cable fault if they used the old down lead or damaged the new downlead on installation, or you have some coax kinked/bent/squashed at some point. This can create a frequency-specific high resistance point that affects a very narrow band. The nearest other RF channel muxes are at 32 and 37. There is a HD mux at Ch.35 though (586MHz, DVB-T2). If the TV can pick this up then see if you get lower Strength and any difference in Quality for this compared to RF Ch.34

 

[Skylark NW]

Thanks again for your help, much appreciated.
I'm pretty sure that the issue is confined to RF channel 34. The corresponding TV programs can pixelate whereas those on PSB1 seem fine.
When the Freeview guy installed a new aerial, he also added a channel 59 filter as his signal analyser showed a strong 4G signal. He did not replace the coax from roof space to the outside aerial as he said it was in good condition (35 years old). I was hoping that he would as the joint between it and the coax installed in the wall space is really crude. The two shields and the two cores are simply wound and taped. That said, it's been like that for 35 years. I keep meaning to make a proper joint but going in the loft is not my favourite pastime.
I checked the wall socket to recorder-in lead and there is no continuity between shield and centre. One end has a moulded plug and the other end a manual plug. I would not be surprised if I shortened this lead sometime in the last 35 years but can't recall doing it.
I removed the leads to measure continuity so took the opportunity to use a bit of switch cleaner. I sprayed the scart leads, too. Interestingly, over the last 24 hours it's been fine. I recorded a random program on Ch4 and playback was ok. I'll record a channel 5 or a More 4 tonight. Still confused..........

 

[Lucid]

Thirty-five year old coax won't be double-shielded, but if it's in-wall it may not matter so much. If you can make time to remake those joints though then that's one potential weak spot eliminated. I'd also have a look at the wall plate. Unshielded versions as would have been the case if fitted 35 years ago are another backdoor for interference issues.

The fly lead shouldn't have continuity between the centre pin and the shield. If it has, then it's broken.

What you're checking for continuity between the centre pins on each end of the cable. Then continuity between the shield connections on each end of the cable.

Most of the moulded coax leads are thin and the shield wire is fairly sparse too. Trying to get a decent connection on a DIY-fit coax plug can be quite tricky. It really is better to just replace the whole lot with something up to modern spec. Short reels of coax cable and coax plugs are available from places such as Screwfix. Their stores cover most of the Manchester region, so for N.Mcr you have Ancoats, Middleton, Hollinwood, Oldham, Swinton etc and most other major towns in the area.

You can by a 25m reel of cable for just over £12.00 You'd then cut off what you need from the reel. The cable is available in black or white outer jacket. Their product name is GT100. Here's a link to the black. Coax plugs are available in male and female versions.

Don't buy their wall plates though. They're crap and unshielded.

Alternatively, if doing the DIY thing seems like a bit too much hassle, then I can make some fly leads for you with Webro WF100 in either white or black, to length, and then post them out.



Your comment about playback being okay at the moment; that fits with a signal being at the cusp point between useable and not.

You may find your signal level varies with atmospheric conditions and day to night. If the level is on the right side of "just enough" or "not too much" for the recorder then it will record just fine. If it teeters on the edge at some point then that's where you'll get signal break-up. As I mentioned in the earlier posts, this level thing could have several causes.

 

[Skylark NW]

I've measured the resistance along the length of the coax lead from wall socket to recorder. The outer shield is 0.2 ohm and the inner is 0.5 ohm.
I've now recorded a random Ch5 program, in addition to a Ch4. I believe that this is also on the Channel 34/PSB2 mux which has given me the problem. It was a windy night so a tree related issue would not have been a surprise. The recording was generally good, very much better than recent experience, albeit there was some occasional jerkiness but nothing to spoil the enjoyment of watching.
I've always believed that electrickery is the work of the devil so either the set has (almost) fixed itself or cleaning the cables has made a key difference. I'm hence thinking marginal signal, not overload signal.
I probably should make a proper coax join in my loft and replacing the two coax leads, recorder to wall socket and recorder to TV may give another small improvement.
I'm walking distance to Screwfix but happy to buy ready made (by a pro). I'll send you a message.

 

[Lucid]

Received and replied