Odd TV Signal Problem - Turned out to be HDR FoxT2

damianiw

Member
Hi

My wife complained we've been unable to get one specific set of channels since last week (those on chan 25 where we live, Really etc).

We've been busy at Isle of Wight Festival, then watching world cup - went to turn on my HDR Fox T2 to watch the Formula 1 and it went through the initial setup!

Had to do a full retune then found the power save was on by default of course disabled this and the good news is I don't have to climb on the roof to fix the aerial!

Bad news is I've missed all programs for the last 2 weeks, I have disable update package installed and a timer set to prevent the box updating it's firmware but thought ah ok an over air update has sneaked through... did a power off and on and then saw the CFW message on the LCD so nope it hadn't

Web interface version: 1.0.15-3 (Lighttpd)
Custom firmware version: 2.16 (build 1691)
Humax Version: 1.02.32 (kernel HDR_1.02.32)

Never had my humax miss a beat before, I looked in crash.log and nothing and other logs dont shed any light on the issue.

Anyone else had this ?
 

Black Hole

May contain traces of nut
Yes, random assertion of the installation wizard is a known "feature".

FWIW, I am having reception problems with some multiplexes at the moment, no doubt down to atmospheric conditions (ie summer).
 

Black Hole

May contain traces of nut
Hmm. HDR3 is at the far end of a long aerial distribution system (the one I have trouble with), and the signal strengths roughly correlate with channel number:

Ch23 51/100
Ch26 51/100
Ch48 50/100
Ch49 51/100
Ch52 44/100
Ch54 36/100
Ch56 30/10
Ch58 0/0

23 & 26 are the local Wales repeater, the rest are Mendip. Note I have not tuned Com7 on Ch33.

This could be indicative of 4G interfering at the top end of the frequency band.
 

prpr

Well-Known Member
And it could equally likely be something else. Why don't you measure at the other end of the cable, or put an amplifier in to overcome the distribution loss in the cable?
 

Black Hole

May contain traces of nut
It was fine until recently, there is an amplifier, and the losses don't show up until attenuated by the cable run.

I'm sure you appreciate the undesirability of multiple amplification stages.
 

Owen Smith

Active Member
It was fine until recently, there is an amplifier, and the losses don't show up until attenuated by the cable run.

I'm sure you appreciate the undesirability of multiple amplification stages.

Is the coax damaged or water penetrated? If it is damp, it will be attenuating high frequencies more than low ones. Is it crappy old "low loss" TV coax, or decent double screened satellite cable?

Is the amp before the long run of coax? If it's after then all you're doing is amplifying noise.
 

Owen Smith

Active Member
Given the signal strength reduces steadily as the frequency increases, I doubt this is 4G interference. It's starting to hurt too low in the frequency range to be 4G.

It looks like crap cable losses to me.
 

Black Hole

May contain traces of nut
Well, it may be - but all but the first few feet are indoors and I'm not going up the ladder for just that! The "low pass filter" has a very sharp cut-off though.

I'm not sure what to expect with 4G interference - whether it will cause an all-band swamping of the DVB-T signal, or be confined to the upper frequencies, and whether any swamping will manifest as a low signal or a high signal with low quality.
 

Luke

Well-Knwοn Мember
I'm not sure what to expect with 4G interference - whether it will cause an all-band swamping of the DVB-T signal, or be confined to the upper frequencies, and whether any swamping will manifest as a low signal or a high signal with low quality.
There is also the N+9 channel interference risk for some receivers. E.g. a 4G broadcast using channel 66 could theoretically interfere with channel 55 but have no appreciable effect on channel 58.
 

Black Hole

May contain traces of nut
Is it crappy old "low loss" TV coax?
Of course it is. At least it's not the ultra-crappy thin stuff. But it's worked as long as the house has been here (until, like I said, recently - so I still think it's some change in the transmission or propagation).

Is the amp before the long run of coax? If it's after then all you're doing is amplifying noise.
Give me some credit!
 

Trev

The Dumb One
Is the amp before the long run of coax? If it's after then all you're doing is amplifying noise.
Not strictly true. The signal loss in the cable will reduce the sig/noise ratio. You will then amplify the resultant signal at this reduced sig/noise ratio.
 

Owen Smith

Active Member
Well, it may be - but all but the first few feet are indoors and I'm not going up the ladder for just that! The "low pass filter" has a very sharp cut-off though.

You say the first few feet is outdoors. If the outer sheath has become UV degraded to the point that it has split or there has been some physical damage, water may have got in. When that happens, capillary action will gradually draw the water along the length of the coax so it could all be gradually getting damp, even the bulk of it that is indoors. The wet cable attenuates high frequencies more that low frequencies. Also eventually the copper corrodes and the entire cable becomes a green soggy mess inside the insulation, I've seen a cable in that state.
 

Owen Smith

Active Member
But it's worked as long as the house has been here (until, like I said, recently - so I still think it's some change in the transmission or propagation).

Have any trees grown taller over the years, such that they are now in the way of the signal but it only shows in spring and summer when the tree is in leaf and growing? (Hence more water in the tree to attenuate the signal.)

Has a building been built in the way of the signal, or even something been demolished that was shielding your aerial from a interfering signal?

And as I said in a previous post, perhaps your cable has developed a fault?

Or your aerial, if it's an outdoor aerial they don't last forever in the weather. The connections inside may have become water penetrated or corroded.

Do your other boxes show a reduction in signal strength on the higher muxes? They may continue to work due to higher absolute signal strength but show the same pattern of high frequency degradation. If they do it points at a common factor before the split (propagation, aerial or distribution amp). If the high channels are the same strength as the low ones on your other boxes then the fault is after the signal splitting.
 

Owen Smith

Active Member
Have you tried swapping boxes around on your different locations? If it's a faulty HDR Fox T2 then the fault will follow the box as you move it to other aerial sockets in the house.
 

Owen Smith

Active Member
and the losses don't show up until attenuated by the cable run.

That answers some of my questions I believe. If the losses only occur after this cable run, it can't be 4G surely or anything else in the propagation.

Except that "low loss" coax is so badly screened that it picks up through the sides of the cable, so interference could be getting in there.
 

Black Hole

May contain traces of nut
Do your other boxes show a reduction in signal strength on the higher muxes?
No.

Be sure I'll let everyone know when and if I find the problem - but I am finding it very hard to believe there is no apparent attenuation at channel 49 and complete loss by channel 58. I really don't foresee cable degradation doing that - so yes, a switch around is in order.
 

Owen Smith

Active Member
but I am finding it very hard to believe there is no apparent attenuation at channel 49 and complete loss by channel 58. I really don't foresee cable degradation doing that

There are times when RF behaves very mysteriously. We employ some RF hardware engineers at work, and they are both some of the brightest people I know and the people capable of the weirdest lateral thinking. I swear one of them can see the RF on the PCB and visualise problems in his head.

At times RF seems like black magic, so while I agree no loss at channel 49 and total loss by channel 58 (or at least goes off the cliff) seems unlikely, it's not impossible.
 
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