Roped in to looking at a freeview/aerial fault, help!

[Tidy Max]

Hi all! A guy at our wholesalers has been asking my boss to go and look at his aerial at his house for over a year now, and the job has been palmed off on to me. I have installed a few aerials and sky dishes but i have never done any serious fault finding with one.

Multiple free view boxes throughout this guys house are freezing and 'going slow' as he puts it. Apparently it will take multiple pushes to change channel and the channels will freeze.

Now i have heard this gentleman is a bit.... money conscious, so i assume these receivers are the £15 sort from Asda. However i think i should show some willing into looking if there is a genuine aerial/signal issue.

Ive been lent a tv meter but i have no idea what reading i should be looking for.

I won't be getting paid for this job so before i get slammed with a barrage of 'get a professional in' please take that into account. After all hes put up with the issue for a year because he won't pay someone to look at it.

Thanks in advance and i appreciate any input as always, even if its just where to read up on the internet. I have done some pretty thorough googling the majority of which recommends using the built in signal meter that's in free view boxes, which in my opinion i wouldn't trust in the slightest. But that's just me being cynical!

 

[bigbaddave]

You say you have a Tv meter, What exactly are you testing the signal with and what are your readings ?

 

[Tidy Max]

Yep its a Horizon HDTV no readings yet because i haven't been to the job. I was supposed to go today but have been let down. I was just wondering what readings i would get if it was a decent signal.

That way i can show the gentleman that its not his aerial at fault and its the nasty freeview boxes.

Or alternatively find it is the aerial at fault.

Thanks for the reply Dave

Sent from my GT-I9300 using Tapatalk 2

 

[Colin_K]

Hi Tidy Max
Before doing anything its worth checking out the signal strength on the digi boxs. Do they have a good signal or not ? If not check out the distrubution system, start with the coax, does it look old ? Digital tv needs modern coax, the old stuff is good for the old analog signals but not alot of use with digital. Dont be tempted to get a cheap roll off ebay, its not normally any good. Go for 'WF100' or even better 'WF125' which is also good for Sattellite feeders. Also check the antenna, is it old ? Does it clear the next door neighbours roof ? Does it aim into a forest? If its any more than around five year old chances are its no good. Many older ones are grouped in bands and may not even cover the frequencies used in your area now. You need to check with local tv company as to which is best for your local transmitter. If the antenna is feeding multiple digi boxs it will need an amplified splitter box, no if's, no but's. it will need it, no matter how close to the transmitter he is.

If you have a meter its worth checking the dB loss in the system. Start as near to the antenna as you can, and see how many dB's you have. Then again further down the system again check the dB's. You will find you get a lower reading. Most decent coax you will find a loss of around 0.2 or 0.3dB per meter. (WF100 is around 0.18dB loss per meter).

If all is in place and the digi boxs are getting a good signal, it could well be an interferance problem, but start with the distrubution system first. It may be worth checking how far he is from the local transmitter, because to stronger signal can cause problems too.

 

[grantr37]

They have an inbuilt signal strength meter in the firmware (tiny little software program that runs the box/decodes the signal/provides the picture and user interface menu) and this is in the set up part of the menu.....shows the signal level in 10 or so segments of a bar......on boxes over £200 or so the actual dB value shows on screen as well.....
What I would do is take another freeview box along and plug that in to see, then look at the Ariel as well...

 

[Leedsryano]

Hi mate,

I agree with colin_K, if the bloke has "multiple boxes" its highly unlikely that they have all developed the same fault,
It also means that somewhere in the system there will be a splitter being used to distribute the various signal to the different boxes,
depending on the signal strength and quality "coming in" to the aerial its generally good practice to not split the signal more than 3 times (in some cases 2 or even at all!) without the use of a powered amplifier or "booster", but this all depends on the actual incoming signal,
My advice (and easiest way) to avoid climbing up a roof to test the aerial would be locate the incoming signal feed, this could be in the loft or stuffed behind a telly its a case of tracing the cable as best you can, give this a test first to establish if its the aerial or incoming coax thats at fault, check for water or moisture in the cable end and look out for general wear and tear, if this tests ok then the problem could be a splitter/amp/booster fault or simply the fact that he is running too many TVs off one aerial. The main clue is that all his TVs have the same fault. little tip if his aerial has a flat rectangular back plate it generally means its a good few years old as they dont even sell these anymore.
Good luck

 

[mhar]

I can see where people are coming from but it is quite possible to run far more than two points off an aerial unamplified. Also it is quite possible to use existing cables and it is perfectly acceptable to use an 'old' aerial. Obviously a new aerial (incorporating a balun), ct100 cable and no splits are going to give the best results.
There is one fundamental principle and that is to make sure that what you are trying to distribute is good enough so your first test must be as soon as possible from the aerial feed preferably at the aerial. Not being familiar with your test equipment I can only advise in generic terms. Pick on the weakest multiplex first as this is likely to be the noisiest and look at the signal (or carrier) to noise ratio where you are looking for a figure (I think according to the books of around 32dB) but I use 25dB as a guide. If you have this you are laughing, if not you need to improve this ratio - at this point signal level is largely irrelevant. Poor ratio at the aerial = change the aerial. Poor ratio at the distribution point but ok at the aerial = change the cable (which usually involves changing the aerial as on most older aerials you have to open a cover and feed cable through a seal which is then likely to not re-seal properly).
Some meters measure Bit Error Rate for individual channels within a multiplex but, as you have a general problem, I would ignore this and try and get an overall view by measuring the c/n or s/n ratios as above. However if your meter has a graphic showing the multiplex make sure that it is a nice even square block with no peaks or troughs indicating signal highs and lows within the multiplex. If uneven use a test aerial to establish if there is an alternative (better) aerial position.
Assuming you now have decent signal at the point of distribution and have all tails running to this point (you don't want to have a splitter on a split leg - two sources of noise ruining your s/n ratio) you then have to determine whether you need amplification. I rarely amplify because I do my best to ensure that I am collecting decent signal - last week 8 points off an indoor unamplified loft aerial, yesterday 140m run from aerial to a launch amp then split into two legs with taps off to 25 different houses some 800m apart (400m each leg) with no further amplification. Amplifiers are so often fitted when not required and can cause a lot of problems.
I think the books say a lot higher but you should be aiming for c/n ratio of 25dB at each point and a signal level of 40dBmV. If you are starting with a decent c/n ratio this will pretty much look after itself, for the signal level on sensible cable runs allow 6ish dB loss per leg (more if wall plates are to be used) + splitter losses (look this up but I will use 10dB in this example as if using a six way split). So 40dB required + 6dB cable loss + 10 dB splitter loss = 56dB signal required pre splitter for this leg. If you only have say 50dB you will need to amplify by 6 dB so I would fit a 10ish dB masthead - in reality I would probably give it a go without an amplifier as a lot of tuners will work on very low signal levels and c/n ratios and we are overestimating our losses anyway. However the point is this is how to design a system and therefore how to fault find

 

[Tidy Max]

Sorry about the lack of correspondance i have been mega busy this week. Just heading off to look at this fault now, once again all your advice is much appreciated! Ill reply again when i get chance and let you know how i get on

Thanks

 

[UKMeterman]

It might be an idea to sketch the system and put a pic here. Make sure all connections are clean and look for any water damage particularly external cables if water gets in coax has had it.

 

[mhar]

It might be an idea to sketch the system and put a pic here. Make sure all connections are clean and look for any water damage particularly external cables if water gets in coax has had it.

Foam dialectric cables should be ok but air spaced cables with water ingress have to be scrapped

 

[Tidy Max]

Yo sorry for the delay again.

I went to the gentlemans house and noticed he had a HIGH gain aerial (looked similar to the x-fighter from Star Wars) whereas the rest of his neighbors just had regular aerials (horizontal blades).

I took the Horizon HDTV and measured the signal from the aerial feed, and then from the tv points.

I pain stakingly wrote down every channels measurement which i will transcribe onto here tonight.

The unit started at channel 21 and went up to about channel 67 i think, the majority of channels had a <25dBv reading and about 10 of the channels had a high reading and DVB-T also lit up on the unit.

Can anyone explain what the channels 21-67 are? Or even better point me in the right direction for somewhere to read up on it?

ONCE AGAIN, thanks for all of your help, its appreciated.

Max

 

[mhar]

The channel numbers are just a way of describing frequencies. Channel 67 is a lot easier to remember than 839.25MHz (that is if I have remembered it correctly!)
Now the fact that you have 10 channels (multiplexes) might be pointing us in the right direction (even though 9 might make a bit more sense). It sounds like a main transmitter plus a relay (6+3) or it could be two main transmitters (6 + another 6 but only four are coming through at a reasonable strength). If the +3 or +4 channels are lower frequency than the wanted 6 (or it could be vice versa if the relay is the optimum transmitter for him) then the freeview boxes would come accross these channels first and store these in it's memory. Quite common when people just amplify signals without realising the consequences. The aerial would not be picking these up 'cleanly' which could explain the problem.
A list of the channel numbers received and their strengths together with the polarity of the aerial (h or v - flat or upright) will help. Also is the system amplified and where did you take these readings from?
Digital uk should have the transmitter information you requested but it could well appear to be in Greek!

 

[Martyc]

From my limited aerial experience (install and fault find on them at work on static caravans, same principle, not as far to fall) the biggest signal killer seems to be multiple or poor joints, then loose coax socket points and finally cheap moulded coax cable from socket to tv. As long as the aerial is sound and facing the right way and the cable is intact these are the simple things I look for first.

 

[mhar]

From my limited aerial experience (install and fault find on them at work on static caravans, same principle, not as far to fall) the biggest signal killer seems to be multiple or poor joints, then loose coax socket points and finally cheap moulded coax cable from socket to tv. As long as the aerial is sound and facing the right way and the cable is intact these are the simple things I look for first.

You have pretty much summed up my dislike of wall sockets except to add that often the cable is kinked when installed in too small a back box!

 

[Tidy Max]

Okay doke, heres the readings, this first lot of readings were taken at the END of the aerial cable
21 to 41 <25db
42 32dBv
45 42dBv
49 38dBv
53 41dBv
54 60dbv
55 62dBv
56 32dBv
57 39dBv
58 64dBv DVB-T
59 64 dbV DVB-T
60 42 dBv DVB-T
61 64dBv DVB-T
62 63dBv
63 26dBv
64 <25dBv
65 <25dBv

These readings are the same at the main tv in the house, they feed a BT Vision box which works fine.
I also took the readings at one of the problem TV's, a Ferguson F2202 LVD
I will only list the readings which were different, strangely, some were higher and some were lower than the original readings, this may mean something very obvious to you aerial guys.

42 37 dBv
45 46 dBv DVB-T (This doesn't have DVB-T at the aerial and is 3db higher)
49 42 dBv DVB-T (+4dBv) BER pass
53 37dBv (-4dBv)
54 59dBv (-1dBv)
57 43dBv (+4dBv)
58 68dBv (+4dBv) Higher dBv however no DVB-T, whereas at the aerial it has 64dBv but DVB-T lights up? BER pass
62 64dBv (+1dBv) DVB-t (BER pass)


Also, when DVB-T lit up the Bit Error Rate menu worked i checked this on every channel that BER lit up on and they all passed.