Lost all channels on the HD Mux suddenly

aesmith

Member
Hi,

We haven't had HD compatible equipment until a month or so ago when we got the Humax HDR-FOX. We're served from a relay so only have the three Muxes 1 (ch58), 2 (49) and HD (54). All were properly picked up when we first did a channel scan.

Yesterday we found we'd suddenly lost all the HD channels, selecting the channel it reports "signal is weak" or something similar. Going to the Menu and looking at Signal Detection we get 100% quality for both 49 and 58 (strength around 45%), but absolutely zero for both on 54. No faults reported on Gartley transmitter which was my first assumption.

Today after messing around, the HD channels are back after carrying out the following ..
  1. Checked aerial cable properly connected at both ends
  2. Soft reboot Humax
  3. Hard reboot Humax (shutdown from remote, switch off power, leave couple of minutes, restart)
Checked after each attempt, still no HD channels and still zero on channel 54

Finally did one more check on aerial connection, and suddenly the HD channels are back. Quality 100%, strength 46%.

Is the HD mux more sensitive to aerial issues? I really would have expected an aerial problem to have affected all channels more or less equally, or the highest/lowest frequencies rather than only the middle one.

Or is it more likely a Humax glitch? Or transmitter problem, we've never had HD before so are they prone to disappear/reappear for no particular reason?

I'd like to understand what might have gone wrong, especially as we had a lot of stuff set to record, and it is a real pain switching the schedule to a non-HD channel without losing the series link

Thanks,

Tony S
 

Black Hole

May contain traces of nut
What you have is a dodgy aerial connection, or leakage between your HDMI cable and your aerial lead. Certainly the HiDef multiplexes are likely to be more sensitive than StDef, the DVB-T2 encoding needs to transport a greater data rate and therefore may well sacrifice some error immunity. You should also check your channel numbers are all correct for your transmitter - see HERE (click).
 

MontysEvilTwin

Well-Known Member
What video mode do you output from the Humax HDMI? If you have a weak MUX, 1080p will cause problems: try 1080i. Do you have a bluray player in your setup? If so make sure that it is in standby while you are watching or recording from the HD MUX as it will almost certainly be outputting 1080p. Also you may find that the reception is affected by weather conditions.
 

prpr

Well-Known Member
Get (or make) a proper aerial flylead, using decent (CT100 or equivalent) cable with a proper copper screen. Those cheap white leads you get free with cornflakes are crap.
If using normal Belling Lee plugs, make sure they are soldered. It's probably easier to convert to F plugs on the cable and use adapters.
 

MontysEvilTwin

Well-Known Member
Get (or make) a proper aerial flylead, using decent (CT100 or equivalent) cable with a proper copper screen. Those cheap white leads you get free with cornflakes are crap.
If using normal Belling Lee plugs, make sure they are soldered. It's probably easier to convert to F plugs on the cable and use adapters.
This is good advice. I replaced all my flyleads with cables made using Webro WF100 (double screened: copper mesh and foil) and replaced my cheap HDMI leads with better screened ones. This has improved things a lot, but I still have problems with the new, lower power HD MUX (BBC Four HD etc.). If my blu-ray player is switched on (it is on a different shelf to the HDR-FOX but is only about a foot away) reception is lost on that MUX. Change your RF cables, as prpr suggested, and see how it goes.
 
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aesmith

Member
Thanks everyone. Sounds to me like the aerial flying lead is the issue, in particular the connector at the outlet end. I need to rework the aerial cabling in any case, but will have to make some temporary improvement just now. Channels are correct, and according to Wolfbane all three have the same ERP. I don't have a Blue Ray player at the moment, only a DVD player connected to the TV by SCART. The only HDMI is Humax to TV, and I haven't bothered with a pass-through cable to the TV either. I'm not sure if these other issues (1080i vs 1080p) for example would be relevant, if the Humax itself says 0% signal strength then I would have thought it was an issue on the way into the Humax, not on the way out. Playback and live viewing have always appeared perfect up to yesterday.

I've also noticed the aerial is a bit squint, it should be vertically polarised but is not quite. I will check alignment as well, do you know if the bearings in these coverage checkers are True or Magnetic?
 

Black Hole

May contain traces of nut
I'm not sure if these other issues (1080i vs 1080p) for example would be relevant, if the Humax itself says 0% signal strength then I would have thought it was an issue on the way into the Humax, not on the way out.
Not so. HDMI signals are at RF frequencies and add noise to the aerial signal if the cables are not sufficiently screened or separated. In particular, 1080p is in the right frequency band and can be problematic.

I've also noticed the aerial is a bit squint, it should be vertically polarised but is not quite. I will check alignment as well, do you know if the bearings in these coverage checkers are True or Magnetic?
I would imagine it is a true bearing, but the slight misalignment caused by the "wrong kind" of bearing or polarisation skew is unlikely to cause a problem - until we get a pole flip!
 
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aesmith

Member
Not so. HDMI signals are at RF frequencies and add noise to the aerial signal if the cables are not sufficiently screened or separated. In particular, 1080p is in the right frequency band and can be problematic.
Thanks, I didn't realise the bandwidth on HDMI was so high. It's cheap cable, so will sort out something better for that. I agree that aerial alignment may not need to be spot on, but I think our aerial has shifted as I can't remember it being that far out of vertical. It's an easy check.
 

Black Hole

May contain traces of nut
Thanks, I didn't realise the bandwidth on HDMI was so high.
Back of the envelope calculation: 1920x1080 pixels (that's 2 million), 3 colour channels, 8 bits per channel, 50 frames per second...

Data rate is about 2.4Gbps.
 

MontysEvilTwin

Well-Known Member
@aesmith. Now I have changed my RF cables, I find that channels like BBC Four HD are fine on 1080i. If I switch the Humax to 1080p output, the signal quality fluctuates leading to pixellation and picture break up. The bluray player nukes this MUX completely. Recabling will help, and as you have no bluray this is obviously not an issue. You might find that you still lose the signal occasionally on the HD channels: if so this is probably weather related.
 

Ezra Pound

Well-Known Member
There are 3 TMDS (differential) channels in HDMI rather than one, each running at about 1.4 Gbps for 1080p
 
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aesmith

Member
Ours worked fine on 1080p from when we first got the Humax until yesterday when HD stopped working altogether. Now they're back, it is still perfect at 1080p. The funny thing is that we don't get any intermittent issues so no prior warning. I can only assume that the connector on the aerial lead was in fact not properly seated either before I checked or after my first check. Neither the cable nor the wall outlet are particularly good quality, so I think I generally need to keep an eye on them until we get a chance to renew the aerial cabling.
 
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