HughieDad – 2 hours ago  » 

This is weird…

We are on the Angus “Highland” multiplex and we were recently instructed to do a FREEVIEW transmitter retune. Among other changes, PICK was moved from Ch11 to Ch34 and was replaced with SKY ARTS. BBC FOUR was supposed to move to Ch55, but our FVP-5000T found no signal at that frequency, despite several attempts. Our LG TV, meanwhile, found BBC FOUR on Ch55, exactly where it should be. It seemed really odd that a single channel should drop out on one device, but not another sharing the same aerial. We reconciled ourselves to not being able to watch or record BBC Four on the Humax.

Then, one day, I overshot on the EPG and stumbled upon BBC FOUR lurking on Ch851! That’s on the Humax, but not on the TV! How bizarre! Are channels being broadcast twice on different modulation schemes, meaning different devices tune into different signals? Or is it a software issue and the frequencies are being rendered onto different channel numbers by the hardware? It seems strange that I can find no mention anywhere that BBC FOUR should appear on Ch851 for anyone!

No it just means you have reception from more than 1 transmitter. The first found BBC4 gets stored at the correct number. the second at the higher LCN,

In your location you need to manually tune the box to the UHF channels your best transmitter uses.

EEPhil – 2 mins ago  » 

grahamlthompson – 15 hours ago  » 

HughieDad – 2 hours ago  » 

This is weird…

Then, one day, I overshot on the EPG and stumbled upon BBC FOUR lurking on Ch851! That’s on the Humax, but not on the TV! How bizarre! Are channels being broadcast twice on different modulation schemes, meaning different devices tune into different signals?

No it just means you have reception from more than 1 transmitter. The first found BBC4 gets stored at the correct number. the second at the higher LCN,

In your location you need to manually tune the box to the UHF channels your best transmitter uses.

Try putting your postcode and house number into the coverage checker https://www.freeview.co.uk/corporate/platform-management and make sure Angus is your best transmitter – if necessary check which way your aerial points. Use the results from the coverage checker to manually tune your Humax.

But don’t forget to photograph your recording schedule and then delete all existing channels after that before you start tuning.

HughieDad – 16 mins ago  » 

Thanks for the replies, everyone. It’s much appreciated. I checked the Freeview Coverage Checker and it just confirmed what I already knew.

We can see the Angus transmitter from our living room, about 15 miles away, up Strathmore. Indeed, I can see 5 red beacons on it now, as I type! The Durris transmitter is a similar distance behind us, but a forest prevents clear line-of-sight. When we moved into this house the analogue picture quality was poor. I found this was because the new, digital-ready, loft aerial was pointed at the Angus transmitter, but through some aluminised plasterboard! So the Angus signal was attenuated and scattered, while the Durris signal was both leaking in through the back-lobe and reflecting in to the main-lobe! I moved the aerial to the other end of the loft and the problems went away. We’ve tuned to the Angus transmitter ever since, with all our TVs connected to the same (large, highly directional) aerial and masthead amplifer/splitter, which has its variable gain turned down a bit to avoid saturation. I cannot see why the TV and PVR should receive different channels.

I always use the SMART TUNE feature because our recording schedule is huge and, like other people’s, the EPG is annoyingly flaky on some channels. However, when this problem arose with BBC FOUR, I tried tuning in to the missing Ch55 frequency manually, but the Humax still found no signal.

I’ve just checked the TVs in the bedrooms. Just like the one connected to the Humax in the lounge, they have BBC FOUR on Ch55 and Ch851 is INVALID. Only on the Humax is it the other way round.

Strange, eh? Perhaps one day I’ll try a non-SMART retune of the Humax, just out of curiosity.

You need to do it now. If you do not you will get big problems with series rocordings that follow the broadcasters start and stop recordings automatic signals that let your broadcaster start and stop your box follow the actual broadcast times,

Incidentally there is no such aerial as a digital ready aerial.

All UK digital TV is transmitted modulated on a UHF analogue carrier. The only detail you need to know is that your existing (analogue) aerial is capable of receiving the range of analogue frequencies that your best transmitter uses.

Analogue aerials are specified by group. A wideband aerial will receive across the whole UHF band using UHF carriers 21-68. The higher numbers are now being used to provide other services.

The difference between former analogue (PAL) services is simply that the modulation (the way the carrier is altered) is digital. The output from the tuners is a stream of zeros and one. Such a stream can be recorded exactly as is to a hardisk. Unlike analogue one UHF carrier can carry multiple channels within the same data stream (multiplexed). The carrier for obvious reasons is known as a MUX – Multiplex.

When watching live the tuner and the box decoding extracts the video and audio from the box. When recording the same stream is copied as is to the hard drive.

When replaying a recording the hard drive delivers the same digital stream to the box decoders. Replay is identical to the original live broadcast.

HughieDad – 1 hour ago  » 

When we moved in and found the analogue picture was poor, I checked that the aerial installed by the developer was the right one for both analogue and the new, parallel-running digital system. That’s what I meant by “digital-ready”. It’s over a decade ago, now, but I seem to recall this was one of those areas where a broadband aerial was needed for DTV, but a narrower-band aerial was adequate for analogue. As I wrote earlier, the problem turned out to be aerial alignment, not the hardware.

The development of modulation schemes as electronics improved is, indeed, fascinating: AM >>> FM >>> PSK >>> QUAM 😯 !

Anyway, stand up Martin Liddle! You get the prize!

I did a NON-SMART retune. The mysterious Ch851 has vanished and BBC FOUR has appeared at Ch55 where it belongs. God knows what the SMART RETUNE software does, but like most of the software on Humax boxes, it only does a half-decent job. I’ll never trust it again. This glitch was glaringly obvious; how many other channel errors have gone unnoticed? How many recording failures have been due to SMART RETUNE scrambling the channel listing? We may never know. Don’t trust it, people!

Thanks everyone who contributed. The mystery of Ch851 is solved.

For most including me it works fine, it’s entirely down to your location and aerial.

Guessing you are in a elevated location and you get signals from more than 1 transmitter. This can be even more difficult if you choose to re-tune during high pressure atmospheric conditions. High pressure extends the the range of more distant transmitters, resulting in duplicate channels.

If you learn how to manually tune your box it will not happen again, If not during the next high pressure uplift you will get the same issue.

So happy you are now OK, but it will happen again.

The steps are basically simple.

Make a note of the UHF carriers that your best transmitter uses and whether the modulation is DVB-T or DVB-T2

Next delete all your Freeview radio and TV channels,

Next manually tune to each of the UHF carriers that you have identified and select the appropriate modulation and save the results. Smart tune has no way of identifying which transmitter it is finding channels from.

It’s not a Humax issue rather your location and also your aerial design that can reject transmitters it is not pointed at.

If you need help to do this next time it happens just ask.