Only used tuners are shown. Record a channel from 2 different mux and watch a channel live from a 3rd mux. Now check the signals. Re the lost channels telling us your local transmitter will help. Changes to the COM 7 and COM 8 frequencies to UHF 55 and 56 may have moved them outside your existing aerial capability. This especially applies to Crystal Palace as the standard group A aerial has no gain at 55 and up.

grahamlthompson – 1 day ago  » 

Re the lost channels telling us your local transmitter will help. Changes to the COM 7 and COM 8 frequencies to UHF 55 and 56 may have moved them outside your existing aerial capability. This especially applies to Crystal Palace as the standard group A aerial has no gain at 55 and up.

I’ve just lost RT HD, 4SevenHD, Al Jazeera Eng HD, and BBC News amongst others. I’m in North London so I think Crystal Palace is my transmitter.

What changed? Is there a solution?

As Graham has already said COM 7 and COM 8 have moved from within group ‘A’ band to UHF channels 55 and 56, which puts them well outside group ‘A’. Also these mux’s are transmitted at a much lower power, which means unless you have a ‘wideband’ antenna, or live in a high signal strength area you will not receive them.

They are only temporary anyway, and some transmitters do not transmit them anyway, mine included.

Graham, we must have been typing at the same time.

MIB – 3 minutes ago  » 

rikki – 1 hour ago  » 

rikki – 1 hour ago  » 

I’ve just lost RT HD, 4SevenHD, Al Jazeera Eng HD, and BBC News amongst others. I’m in North London so I think Crystal Palace is my transmitter.

What changed? Is there a solution?

I’m from just outside London but Crystal Palace is my transmitter. I’ve suffered the same problem, which I’ve discussed in the latter pages of this thread: the-receiver-is-not-receiving-a-signal

I found out today that the receiver in my 4000T isn’t strong enough to pick up the signals for these channels and is not reading the new transmitters at all; I can get them on my TV but not my PVR so I can’t record on them (or have to use the SD equivalent for HD channels).

Seems strange afaik the erp hasn’t changed just the frequency. The one thing that determines how much signal you get is the gain curve of the aerial you are using.

Look at the 2nd link in post 5.

My 5000T (essentially the same box) works reliably using a loft mounted log 36 with a signal strength of just 40% (quality 100%). You can have too high a signal strength especially if using amplification). It might sound odd but in your case adding a variable attenuator might fix the issue. Humax boxes in general have sensitive tuners, probably capable of using a much lower level than your TV needs, I would try reducing the level.

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There is another factor that may affect some, COM 7 and COM 8 will share the same UHF channel numbers for all transmitters that have then. This arrangement is known as a Single Frequency Network. They use a calculated guard interval to attempt to avoid one transmitter interfering with the others. In some locations this may not work very well.

As an example the transmitter I use (Lark Stoke) is a SFN with Bromsgrove and The Wrekin.

A while ago something went wrong with the guard interval setting at one of the group, it screwed up my terrestrial reception till they fixed it.

As more transmitters join the SFN it’s possible this may screw up reception for some viewers who’s transmitters haven’t changed anything.

It’s not a Humax issue at all.

Your so called engineer should have used a spectrum analyser to analyse the actual conditions.

Basically in laymen’s terms.

Every amplifier has a range of input voltages that the output is linearly amplified to be the same but larger than the input.

That means the input waveform is the same as the output but at a higher level.

If the input exceeds the max level the voltage output gets clipped distorting the output.

Designing a tuner has two basic compramises.

Making one sensitive means that it will work in weak signal areas but will be driven beyond the point where the output faithfully follows the input. This is very easy to fix, simply attenuate the input to a level that the sensitive tuner can cope with. This process reduces both the signal noise and signal level equally.

A less sensitive tuner needs the original signal to be amplified, this also increase the noise at the same time.

In the end without a real engineer looking at the actual signal, a cheap variable signal level reducing device as linked connected to the 4000T input may well sort the issue.

Frankly whoever you paid to sort this out should have known this already.