Digital tv loft aerial not working

Discussion in 'Electricians' Talk' started by aak, Feb 15, 2018.

  1. Lectrician

    Lectrician Screwfix Select

    As I have said earlier, although the aerial is the wrong one for the transmitter, it will still pickup some channels. It is group C/D, so will pickup from Ch48-Ch68 happily (and well). 8 of your MUXes from Winter Hill are in this range, so you would pickup around 100 channels with your aerial. There are two MUXes that are outside the group C/D, which is why a wideband aerial is recommended. It would not prevent you picking up over 100 channels though, so I doubt the aerial is to blame. Sure, you need to replace it to pickup all the MUXes, but you should be getting some channels for sure with that aerial. I still ebb on the side of the PSU or Masthead Amp.
     
  2. aak

    aak Member

    In a normal situation as above would a direct test of he aerial before running through the mast amp normally give a decent reading? After I only picked up one green led I assumed that meant the aerial was insufficient/poorly oriented. If that one green led light isn’t indicative of much I’ll make the switch of the amp/psu.
     
  3. Lectrician

    Lectrician Screwfix Select

    The mast head amp is normally used where there is a significant run of cable from the aerial to the distribution amplifier. It looks like yours are almost next to each other? It could be the aerial is a little under sized for the job - 40km is a long way, but I don't know your geography or topography - Are there hills in the way for example? It is a small aerial to be in a roof. One that size would be OK in a roof if the signal was strong.

    To me, as it worked once, and now doesn't, I wouldn't immediately blame the boringly simply aerial. There is nothing in it to "fail". If it was outside, you could blame water ingress, but it is just a simple aerial in a dry loft. It won't "break". The electronics in the mast head and PSU will go wrong though, and regularly do.

    The aerial is not the correct one for your transmitter, but will still pick up most of the stations available. In my opinion, if it once worked, it still will for those stations. You need to look at the masthead and PSU first, then onwards from there.

    You got one green light pre mast head. What did you get after the masthead? Even if you got full lights after the masthead, with your simple meter it would display full lights if the signal being recieved was strong, but it would take no account of the quality of the signal. It could be a strong signal of broken garbage.
     
  4. aak

    aak Member

    Understood.

    Post masthead it was a flickering one light. No one in the house recalls having seen the aerial work but it was a new build bought by the previous owner so I would be surprised if it didn’t work once. And yes, between aerial and distribution amp is a very short distance of a few meters.

    The areial is about 120cm long in terms of size and I believe the surrounding area is pretty flat. The online guide suggested good reception in the vicinity.

    I will go back to visit in a week or so, and in the first instance will see if I can test the signal pre masthead with a tv. I suppose that’s the only way to see what signal I have to play with. Is there a possibility at this point I can get a decent signal but too low power to work with a tuner, without the masthead amp? The desire is only a dozen or so watchable channels.

    I’ll then switch the amp then psu and look at the distributor if each step fails to resolve the problem!
     
  5. Lectrician

    Lectrician Screwfix Select

    If the masthead amp is there, it is likely needed (although odd it is only a few meters from the dist-amp). You *may* find you get some channels from just the aerial, but you may get nothing without some amplification. Certainly if you try to the aerial direct, keep the coax SHORT. You won't loose anything between aerial and TV then. The masthead amps are designed to boost a GOOD signal at the aerial so that losses are tolerable down the coax. They are NOT designed to boost a poor signal. You need to boost a GOOD signal otherwise you are just amplifying the good and bad that comes in. Masthead amps are called masthead as they are designed to be really close to the aerial, at the top of the mast. They will boost the all ready GOOD signal from the aerial, so as the signal goes from the masthead to the distribution amp, the signal that is lost will not result in a poor signal at the distribution amp.

    Your install seems a little odd in the fact the masthead amp is boosting the signal to travel just a few meters.
     
    aak likes this.
  6. KIAB

    KIAB Super Member

    I would start with a new aerial suitable for the range to transmiter, & try it with out all the amp,etc,connected, & see what channels you get & picture quailty is like, then add in the other parts back in bit by bit, you might find the degrade the signal.

    How many rooms do you want to serve with a tv signal?
     
    Last edited: Feb 21, 2018
  7. aak

    aak Member

    Got it - I think I know what to do upon my return and will report back! Thank you again.
     
  8. aak

    aak Member

    There are wall points all over the house, presumably using a bunch of those 14 outputs from the dbn amp and splitter, although there are a bunch of cable ends up there. There is only one point that will be used by my parents though in a bedroom. I figured if there is a fix to sort everything out I might as well and if not I’ll get a professional. We tried a couple of internal next to the tv aerials but the results were poor.
     
  9. Lectrician

    Lectrician Screwfix Select

    It seems like an obvious thing, but the TVs are digital?
     
  10. aak

    aak Member

    It did receive cable media before so I’m assuming yes. It’s not very old.
     
  11. MGW

    MGW Screwfix Select

    This may not be the case with you, however mother has a mast head amp, and living some distance away I got a aerial installer to test the system, with the idea it would need a new aerial, however he got a great signal and plugged in TV and working great. Next day not working again, when ever I played did not matter what I did it would work again, then next day nothing.

    I was really pulling my hair out. Then I removed to power supply for the mast head amplifier, and instead turned on power to mast head amplifier in the TV. This worked, then we got a bigger TV with no DC output to aerial so also bought new power supply, however old fault returned, the mast head amp used had two outputs, so put old power supply on one, and new power supply on the other, at long last it worked.

    It does seem that for whatever reason the amp wanted more power than the power supply could supply so power supply was closing down, never understand why, but power supply 12 volt yet TV output 5 volt both seem to work amplifier. If I could reach the amp without scaffold I would remove it, However the whole point is a mast head amplifier needs power up the coax. Although easy to test unplugging coax cable that you have 12 volt, there is then no load, so it may show OK but once connected nothing.

    Since you can reach the amplifiers try taking them out and bypassing again and again I have found amplifiers have failed, likely saving the TV, electrical storms can take out amplifiers and TV,s and it is normally the first device which gets it, OK with you in a loft so unlikely but replacing or bypassing an amp is first test.
     
    aak likes this.
  12. aak

    aak Member

    Thanks for that!
     
  13. aak

    aak Member

    a late follow up to this old thread, after being prevented from redress due to snow and then a cricketing injury(!)

    unfortunately, my attempts have failed!

    only had an LED tester to measure the signal, knowing that it wouldnt be testing the signal quality. wasnt able to get a short cable tv up there to test more accurately. I did get a solid green directly from the existing aerial which was no different from the new aerial I bought to test, and the output after the PSU was 2-3 LEDs as might be expected ie some amplification.

    swapped out the PSU and masthead amp, with no discernible change on my inaccurate LED meter. put back in the original amp - no change- put back in the original PSU - no change.

    the distribution amp was the next port of call, and something I should have checked right at the start - I did check the output from the PSU, but this didnt match the input to the distribution amp, so I figured it wasnt even worth swapping out the distribution amp.

    and this is where I am stuck. I would have expected that the exit of the PSU would lead straight into the distribution amp, but it doesnt. both cables (exit from PSU, and entry into distribution amp) run out into loft distance under loads of insulation - I wasnt able to easily chase through where it went beyond a few rafters and at that point gave up and thought perhaps it might be worth calling in a professional.

    does that set up sound right? where might those two cables be heading out to?? im guessing either they join up somewhere and either the its so long a cable the signal has attenuated, or they dont and thats the problem. the set up is so neat, its surprising that there would be any obvious installation errors.
     
  14. Lectrician

    Lectrician Screwfix Select

    Those two cables likely go to somewhere where a signal is being injected. It used to be common to take the feed in and out of (for example) a VCR when they were expensive, so you could watch the VCR everywhere. More recently, the same with Sky boxes and even CCTV and door entry. I would guess something that was installed has been removed - The two cable need joining together, either at their final location, or in the loft - Simply by pass.
     
    aak likes this.
  15. HarDeBloodyHarHar

    HarDeBloodyHarHar Active Member

    Sounds like it is time to start from scratch. PSU to masthead/aerial, PSU RF output to telly/Set top box.
     
  16. aak

    aak Member

    its been a while but only just managed to get back to try this and bingo - thats all it was. I owe you a debt of gratitude, 100+ very clear channels now, two elderly pensioners very happy, and lots of good wishes to you. thanks v much!!
     
    KIAB likes this.
  17. Lectrician

    Lectrician Screwfix Select

    What had been removed?
     
  18. aak

    aak Member

    No idea, it was too difficult to chase the wiring from the loft and no one in the house can remember anything that had been removed, or knew of a media cupboard. Probably happened before they moved in sixteen years ago. I marked the wires i cut with a small note just in case of future diagnostics, and made the bypass as you suggested.
     
  19. KIAB

    KIAB Super Member

    Simple!:)

    Glad it's sorted.
     
    aak likes this.

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