Anyone know a lot about digital TV reception (apart from the Chump. of course)

[Boac]

For some time now I have had frequent pixelation on the BBC Mux from my local transmitter. That MUX is broadcasting on 694Mhz, whereas all the other Muxes (which are fine) are much lower - under 600. Pixelation on that Mux much worse with high pressure and wind and rain.

I have the correct aerial. I have an amp. I have checked all the cables and connections, and asked everybody and his/her dog for help, but none cometh (including the BBC). I have put a 700Mhz filter in circuit in case the mobile bands are causing problems. No change, just a slight attenuation as expected.

What is it about the higher frequency that could cause this? This seems to defeat everyone and is very annoying!

[Pontius Navigator]

BOAC, anaprop. Clearly frequency dependent and can be much lower.

I have received Italian commercial VHF in East Anglia, also X-band with the European coast appearing off the UK coast. Even visual with the Isle of Man visible from a beach 65 miles away.

It is quite high today but extremely high.

Just lucky I guess.

[Boac]

Normally only with ducting in high pressure systems? I should also mention my neighbours either have not noticed(!!) or are not experiencing it.

[Pontius Navigator]

Usually I believe. I know we could pick up Greek TV on Akrotiri, about 550 miles and I was told how one crew saw Akrotiri shortly after getting airborne from Malta. Both high pressure systems.

[Boac]

This happens with low pressure as per post#1!

[ian16th]

Aerial propagation and reception is not a science, it is a black art!

[Pontius Navigator]

This happens with low pressure as per post#1!

Your turn, lost me.

Pixelation on that Mux much worse with high pressure and wind and rain.

[Boac]

My turn, then - I thought you understood Met!

"This happens with low pressure............Pixelation on that Mux much worse with high pressure and wind and rain.

Wind and rain normally associated with low pressure systems in my experience? Perhaps you have had a different met experience?

Your turn. - and why not the neighbours?

[Pontius Navigator]

my neighbours either have not noticed(!!) or are not experiencing it.

Not noticing is one thing, not associating it with a problem, not experiencing it as they are watching different channels etc

[Boac]

"as they are watching different channels" - PN I am discussing the BBC Mux.

A major collapse of signal this AM on that Mux - in my house.

[Boac]

Well, some progress, I think. Despite previous exhaustive trouble-shooting (these 'intermittent faults' are always a problem -"Is my indicator working -Yes/No Yes/ No...." ) I may just have tracked down the problem. I have had a very good TV amp since 2008. Today I dug out my old amp and replaced it and so far the problem has vanished. Time will tell of course, but it might be that there was an unusual intermittent fault on the top end frequencies in the amp. Weird!

[TheGreenGoblin]

I was going to suggest interference in the vicinity of the equipment, that powered nodding duck perhaps, but as you have identified the issue as being your amp I will refrain from any further attenuation on this subject.

[Boac]

but as you have identified the issue as being your amp

I only 'think' I have identified, it, Sir. Time will tell as with all 'intermittents'.

How do you know about the nodding duck?

[barkingmad]

Pardon me for arriving late at the party!
I noticed you said the Mux's were quite far apart, can you recognise which of the 'old' channel numbers they're transmitting on?
Since digital changeover the stations have been playing musical chairs with the Mux's and therefore the actual programme numbers, so as a result oop north I have been exhorted to frequently retune my digi kit quite often since DCO.
Has your aerial been 'adjusted' by the south coast winds or indeed do you need to choose a 'frequency-tailored' relatively new aerial to cope with the channel/Mux positioning between 21-68?
When you have retuned do you perform a 'flush'* operation first before installing the current/new set of channels?
This aerial site is a mine of location-specific info as well as general chat about aerials and provide excellent service and good quality aerials should you require a replacement.

https://www.aerialsandtv.com

* "Flush tuning' is removing the aerial connection, preferably at the actual equipment socket so's the remaining lead cannot act as a short aerial and feed in a weak signal.
Then run the full tuning operation so that any 'stubborn' channels get edited out, I couldn't get Film4 some years ago after a channel shuffle until I fell across this trick.
Then plug in the aerial co-ax plug and rerun the tuning sequence-I always use auto being not too sharp on manual freqs. Hopefully any channels reluctant to change will have co-operated.
PM or e-mail me if any queries which need a natter.
There is also a brilliant website into which you plug your postcode and the particular transmitter you're receiving and it shows a pretty coloured elevation diagram showing if there are any orographic obstructions between your location and the transmitter, for which I would have to hunt. Try this- http://www.megalithia.com/elect/terrain.html
Lastly, since my favourite wind turbines were installed at the valley edge near the path from my main Tx to my aerial, there are reports of interference to some in the village who got free sat dishes and boxes courtesy of the wind farm company, so there's another potential troubleshoot!

[Boac]

Basically ticked all the above as per OP.
"I noticed you said the Mux's were quite far apart, can you recognise which of the 'old' channel numbers they're transmitting on?" Can you elaborate on what you mean by the 'old' channel numbers? Do you mean which channel the BBC Mux is on or are you talking about the programme channels? It broadcasts on CH 48.

I should have updated the thread. Has a significant 'research effort' on a Digital forum. It turns out that my 12db amp was PERFECT for all muxes except the BBC MUX (PSB1/BBCA). Plugging in my old amp IN SERIES (yes, I know) and using the low amp output (6db) has sorted the issue with the BBC Mux. Removed the 700 filter and re-flogged it on Ebay.

[barkingmad]

The Mux is tx'd on one of the 'old' channel numbers.
As you run the tuning cycle, if there is a progress bar it will hop from unused channels to the next relevant one, then pause whilst the data is captured, then move on. Watching that progress bar will give you a clue as to where in the spread your particular Mux's are located.
There are also sites which list the Mux's from your relevant transmitter under the old channel numbers.
But if some of your Mux's go out at the lower end near Ch21 and some are way up towards CH68 then you may need a wideband aerial to cover that spread.
Otherwise if they're all grouped towards one or other end of the 21-68 spectrum, then a 'grouped' aerial may get better performance.
This part of the aerialsandtv site makes excellent bedtime reading, all you've ever wanted to know about Mux's etc but were too afraid to ask!

https://www.aerialsandtv.com/knowledge/ ... reeview-tv

Then try this section.

https://www.aerialsandtv.com/knowledge/aerials

The 'Knowledge' section has almost too much to peruse but hopefully you might gain, excuse the pun?

[Boac]

I gave you CH 48(690Mhz) - is that what you were asking? My current Muxes are on 29-48 (post 700Mhz clearance.)

"There are also sites which list the Mux's from your relevant transmitter under the old channel numbers." Yes, and one of them is woefully out of date!

[barkingmad]

There, I’ve done your homework for you!

The answer to Q. # 43 is;

https://www.aerialsandtv.com/knowledge/ ... el-numbers

IIRC from my sojourn near Bournemouth around the Millenium, a lot of sarf coast TV reception was being buggered up by Frog TV channels who didn’t appear to be obeying the rules and international conventions regarding frequency-accuracy and strength etc.

Good luck in your research.

[Boac]

Thanks, but being 'late at the party' I will repeat - my research was over a while back. You are correct about the atmospheric ducting (see earlier posts) but this was extremely evident around Christmas when large swathes of the south of UK lost Freeview and not affecting my issue.

None of the assembled genii (including the Chump) were able to explain the problem I was having with 48, but no matter, since applying the gargleblaster has sorted it out.
(PS The answer is 48)

[k3k3]

Shouldn't it be nearer 50? 42 plus VAT?