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HD channel passthrough since digital retune

Lawrence

New Member
I have my hummy between the antenna and the distribution amp for the house and a few weeks ago all of my HD channels and other random channels disappeared from the TVs scattered about the house.
As all the TVs are new Samsungs, I realised this was because they were all set to standby autotune and this was why the channel listing had changed. The question was why?
I first suspected it was the distribution amp so a purchased a new one. Problem was still there. I spoke to a neighbour who is a TV repair guy about a new antenna but he said I already had a wide band that covered the new channels carrying the new allocation (we are on Mendip).
He then said do I have a Humax and I said yes? has said unplug the antenna in and out and plug them together. Bingo! problem solved.
So to fix the problem in the whole house, I have now added a splitter instead of the passthrough and all is good. So there is obviously some low-end filtering going on in the RF modulator in the Hummy.
Now I need *also to decide if it's worth paying £200 for the new Labgear HDMI>DVB modulator to rebroadcast the hummy around the house.

Has anyone else used one?
4186

*edited to add the word "also" to correct the grammar and remove ambiguity
 
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Ezra Pound

Well-Known Member
Lawrence : I need to decide if it's worth paying £200 for the new Labgear HDMI>DVB modulator to rebroadcast the hummy around the house.
Are you saying that before you installed the splitter (when the Humax was 'feeding' the distribution amp.), that you could tune-in to the humax on any TV that was connected to the amp?, that would mean the Humax was modulating it's own output onto the UHF and as far as I know it doesn't do that
 
OP
Lawrence

Lawrence

New Member
Are you saying that before you installed the splitter (when the Humax was 'feeding' the distribution amp.), that you could tune-in to the humax on any TV that was connected to the amp?, that would mean the Humax was modulating it's own output into the UHF and as far as I know it doesn't do that
no sorry I wasn't, it was a supplementary question as I came across the encoder when I was searching for a wide band splitter.
 

Trev

The Dumb One
I wonder if the Hummy was adding just enough gain to push the sig level 'over the top' for the TVs? I think the Hummy adds a couple of dB gain, so by removing it and adding a splitter will reduce the sig level compared with the original setup of about 6dB lower. What sig strength/quality readings do you get on the Hummy and what it was before on the problematic TVs?

I have a similar device to 'broadcast' my Hummy on LCN8 (I also shift BBC One HD to LCN7), but mine is one of THESE and you get the Hummy's picture in glorious HD. One point to note though, I had to put a variable attenuator in the modulator's output otherwise I got blocking on the off air TV channels.

I take the output of the mod, shove it through the var atten and then through a 'reversed' splitter into my dist amp.
When reversing a splitter, if you need power pass for a mast head amp, watch out as they seem to pass 'the wrong way' (via a diode) when reversed.

Why do Freeview leave LCNs 7 and 8 un-allocated?
 
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OP
Lawrence

Lawrence

New Member
Is there? I have not found that to be the case.
It was more of an assumption due to the fact that the HD carrier had moved down much lower in the channels at the last retune.

I like @Trev's suggestion that it might be gain that is the issue, although just taking the hummy out of the loop fixed it, the splitter was added after it was working to give the hdr a feed again.
The TV said the signal was 77% with 100% quality on the channels it was getting. I also tried the gain control on the new distribution amp and it made no difference, only the removal of the hummy had any effect.

Oh well I have a working solution now so I'll have to put it down to An "Arthur C Clarke's mysteries of the unknown"
 

everthewatcher

Forum Supporter
I have my hummy between the antenna and the distribution amp for the house and a few weeks ago all of my HD channels and other random channels disappeared from the TVs scattered about the house...
This has the mark of a termination/impedance mismatch issue in a cable that's knocking out a multiplex or two.
 
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/df

Active Member
...
I like @Trev's suggestion that it might be gain that is the issue, although just taking the hummy out of the loop fixed it, the splitter was added after it was working to give the hdr a feed again.
,,,
If your distribution amp has any sort of gsin and your antenna has good reception, the increase in DVB-T/T2 transmission power after Digital Switchover (2011 IIRC) means that you might need to put an attenuator between the antenna and the amp, to avoid clipping the signal. Presumably the recent retune event for your transmitter moved channels to a frequency range with less attenuation and took the system over the edge.

My distribution system has a minute sweet spot for the attenuator setting. I hypothesise that this setting just reduces the power enough to avoid clipping in the amp and with the high power muxes at the end of the short tails driven by the 4dB outputs, while still providing an adequate signal for the low power muxes (C Palace: Local, COM7, COM8) at the end of the longest tail using a 16dB output.
 
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