Tuning problems

penshaw

Member
I have two x HDR T2's linked in series from a single outdoor aerial to a Panasonic Smart TV. Each HDR T2 is connected to the TV by separate HDMI leads.

I am tuned into the Pontop Pike transmitter and I have had no problems with this set up .....until last week when Channel 33 (570 MHz) suddenly stopped transmitting ( This outputs 17 channels including BBC4HD and BBC News HD )

After a couple of days I was able to retune the TV to channel 33 with signal Strength and Quality both at 100% ( Both HDR T2's were on standby) and all the TV channels are working fine.

This is where the problem starts: If I try to retune the 2 x HDR t2's the signal strength reaches only a max of 60%, which results in bad pixilation. But also when either, or both of the HDR T2's are switched on the channel 33 programmes on the TV tuner become pixelated and the signal strength on the TV tuner drops below 50%.

No other channels but C33 are affected.

I would appreciate any help on this as I am totally mystified.
 

MartinLiddle

Super Moderator
Staff member
I am tuned into the Pontop Pike transmitter and I have had no problems with this set up .....until last week when Channel 33 (570 MHz) suddenly stopped transmitting ( This outputs 17 channels including BBC4HD and BBC News HD )

After a couple of days I was able to retune the TV to channel 33 with signal Strength and Quality both at 100% ( Both HDR T2's were on standby) and all the TV channels are working fine.
The first thing I would check is whether there is any evidence of water getting into the aerial cabling or whether any joints in the cabling are correctly made.
 

Trev

The Dumb One
.until last week when Channel 33 (570 MHz) suddenly stopped transmitting
Do you really mean that it stopped transmitting, or was it that you couldn't receive it?
 

Black Hole

May contain traces of nut
Could be HDMI interference.

60% strength should be fine (on the Humax scale). Have you re-routed the cabling lately, could you have brought the HDMI leads into closer proximity with the aerial cables?
 
OP
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penshaw

Member
Hello and thank you for your responses.

1) Aerial: I wondered if the aerial was faulty but every channel on the TV tuner is working 100%. Also every channel except C33 works fine on both recorders.
If the problem persists, I'll get the aerial guy to have a look next Monday when he's back from holiday.

2) C33 is the only channel I've had a problem with, it went off on the TV and both recorders at the same time on Xmas day and came back on 3 days later. I can't be 100% sure that the transmitter was at fault but that's what it looks like.

3) 60% signal strength does allow the tuners on the recorders to find the programmes but they are badly pixelated.
I've checked and the HDMI & aerial cables are well separated and I have unplugged/plugged them to ensure good connections.

What is really puzzling me is why the TV works 100% when both recorders are on standby but C33 programmes pixelate when either or both recorders are switched on from standby.

All other channels on the TV and both recorders have continued to work faultlessly at all times.

Any further input will be greatly appreciated.
 

Black Hole

May contain traces of nut
Just to rule out the HDMI issue, try it with the HDRs not in standby, but with their HDMI leads disconnected.
 
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penshaw

Member
Hello again,

If I disconnect the HDMI leads from the recorders the problem with C33 distortion on the TV disappears and the signal strength and quality remains at 100% even with both recorders switched on.

Not sure where this leaves me now?
 

Trev

The Dumb One
Well, at least you have found the cause. It's likely HDMI radiation being picked up on the TV aerial coax. Is it one or both recorders' HDMI leads that are causing the problem? Can you not re-route the HDMI cables or the aerial coax to keep them apart?
What quality aerial patch leads have you got feeding the TV etc? If they are the el-cheapo with the moulded ends, bin them and get some decent coax and make up some new ones. Better screened HDMI leads?
 

Ezra Pound

Well-Known Member
It is sounding like the signals from the HDMI leads are causing the problem, if re-orientating the leads does not fix the problem, you could try changing the V-Format on the Humax Remote from say 1080P to 1080i or vice versa
 

Black Hole

May contain traces of nut
The problem could be reduced signal levels allowing for the HDMI interference to overwhelm C33 when previously it didn't, and the reduction in signal could be external or internal. Has the recent bad weather (strong winds) affected aerial alignment? Has the weather got into the signal path?

Maybe the signal is nothing you can do much about. In that event, you need the best quality UHF coax and connectors for the internal patch leads, and/or decent quality HDMI leads with adequate screening. Keeping the cable routing apart helps.

Changing the video format output from the 'Foxes will alter the frequency of the interference. Simply changing from 1080p to 1080i will halve the bit rate on the HDMI, and not affect PQ to any noticeable extent (the TV will then convert 1080i to 1080p internally, instead of the Humax doing it).
 
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penshaw

Member
Changing the V-format from 1080p to 1080i has fixed the problem !! (thanks EP &BH)

Also tonight the signal strength on C33 is showing at 70/75% on both recorders which allows tuning of good quality images.

The signal quality/strength of C33 on the TV tuner is now 100/100% at all times.

Thanks to everyone for their input, it seems to me that the C33 transmission was interrupted for a few days and then came back at reduced power, which is slowly being increased back to normal.

I'll check the C33 signal strength again in a few days time and report back.

Thanks again.
 
OP
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penshaw

Member
"Oh, I see. Sticking plaster rather than a proper solution."

What a strange crass thing to say !!

I don't follow, it was you who suggested the solution and I already have the best quality aerial and HDMI leads.
 

Luke

Well-Knwοn Мember
Simply changing from 1080p to 1080i will halve the bit rate on the HDMI....
Doen't the frame rate change from 25 to 50 therefore keeping the overal bit rate much the same though the bandwidth profile will change?
 

Black Hole

May contain traces of nut
"Oh, I see. Sticking plaster rather than a proper solution."

What a strange crass thing to say !!

I don't follow, it was you who suggested the solution and I already have the best quality aerial and HDMI leads.
Changing the HDMI data rate is a quick fix, not a solution. If there is cross-coupling between HDMI and UHF, you can't be using the best leads or there is a fault in the screen grounding.
 

Black Hole

May contain traces of nut
Doen't the frame rate change from 25 to 50 therefore keeping the overal bit rate much the same though the bandwidth profile will change?
Maybe, but I thought 1080p is a full frame per 40ms and 1080i is half a frame per 40ms. If 1080i is still a full frame per 40ms, there is very little point in having it at all - and there would not be sufficient change in the emissions to have the observed effect.
 

Luke

Well-Knwοn Мember
Maybe, but I thought 1080p is a full frame per 40ms and 1080i is half a frame per 40ms. If 1080i is still a full frame per 40ms, there is very little point in having it at all - and there would not be sufficient change in the emissions to have the observed effect.
There would be a change in ommisions as the bandwidth profile would change from a full frame starting every 40ms to a half frame starting every 20ms.
 

Trev

The Dumb One
"Oh, I see. Sticking plaster rather than a proper solution."
What a strange crass thing to say !!
I don't follow, it was you who suggested the solution and I already have the best quality aerial and HDMI leads.
Not crass at all. It has enabled you to find out what's causing your problem. It's crap leads. You can choose to fix the problem by using better leads, or still have the problem but do a sticking plaster job that conseals the symptome. I think that the former would be the better option. Although, if you are happy with your 'solution', then stick with it.

PS it wasn't BH who suggested the fault finding technique anyway. It was EP
 

Black Hole

May contain traces of nut
There would be a change in ommisions as the bandwidth profile would change from a full frame starting every 40ms to a half frame starting every 20ms.
Not by much! The primary consideration is the symbol frequency, which is the first harmonic. To all intents and purposes the symbol frequency for 1080i will be half that of 1080p.

(1920x1080 pixels)x(3x8 RGB data)x(25 frames per second)/(3 serial channels)=400MHz (roughly).
 
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