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Loop through connection problem between pvr andvTV

Discussion in 'Audio Visual' started by Longshanks, 9 Jun 2021.

  1. Longshanks

    Longshanks

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    Hi All

    We have a TV in the conservatory, which is fed by a split cable from outside aerial. (Split in loft to feed bedroom TV and the one in conservatory) The aerial was fitted a few weeks ago, and signal strength and quality is v strong. I bought a Manhattan HD pvr, but have some issues. The coax from the splitter goes into the pvr, then looped to tv via another cable. (Pvr also connected to tv with hdmi) The PVR, when switched on, works great. I’ve tuned channels, including HD, and live tv and recordings good quality. However, when watching tv, the picture pixelates, so I can’t watch tv and simultaneously record two channels on pvr, like others. (TV works fine, when cable plugged directly to TV)

    The issue is the loop function and connection. I’ve enabled loop thru in pvr settings, changed loop cable, changed hdmi etc. When the TV picture pixelates, the signal strength stays as 10/10, but the signal quality drops dramatically. I rang Manhattan and did the various checks, software etc. They’d never had this issue reported, but narrowed it down to dodgy pvr, dodgy cable or too much signal!! I’ve researched and now attenuators sometimes required. However, signal is obviously not too strong for the pvr, or when directly connected to tv. I also know hdmi interference can cause issues, but using one supplied with Manhattan, and positioned away from coax.

    I’m about to take the pvr back for a replacement, but suspect it’s systemic.

    Anyone else resolved this issue?

    Apologies for length of this.

    Thank you.
     
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  3. Lucid

    Lucid

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    A couple of possibilities here:

    1 - too much signal level at the TV. Your Manhattan might be adding a little boost to the RF loop out. If the TV you have has a tuner that's a little more sensitive than the Manhattan then it could just be tipping things over the top.

    Try taking the Manhattan out of the equation. Unplug the loop-through connections can connect the male and female plugs together. Try the TV now. Does it still pixelate? If not, check the signal level and quality. Watch for any variation in Quality. Now, try switching on the Manhattan. This will energise the HDMI cable. Whilst still watching TV via RF (Freeview), and looking at the Quality reading, do you notice any change in the readings? (see point 2)

    2 - poor quality RF extension lead - These have weak shielding, and so are prone to pick up radiated interference energy from nearby HDMI cables. If the signal Strength and Quality are okay when the PVR is in standby, but you get issues when it's on then that would point to needing a better coax lead from the PVR to the TV.


    Try the tests above. Compare signal quality looped through and bypassed. Also compare Quality with the PVR in standby versus On. Let us know how you get on.
     
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  4. Longshanks

    Longshanks

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    Hi

    V prompt, clear and constructive. Ta

    1. Should have mentioned that I’d already tried joining the loop coax to the incoming and connecting to tv. Signal is great on quality and strength in that scenario. Quality 100% and strength >90% on all channels.

    Switched pvr on and no change to quality or strength of signal while connected directed to tv.

    2. Just to be clear, TV picture is breaking up, whether pvr in standby or on! I don’t think I made that crystal clear in first post. It’s almost like the mere act of enabling the loop in pvr settings precipitates a jolt to the tv settings.

    I can’t be sure, but don’t think it’s coax used for loop. Bought Belkin and another one with screened connections etc.

    I think it’s more to do with the TV. It’s an ancient, budget Panasonic which only has SD freeview. (One of the reasons for buying pvr)

    Not sure if it’s worth me replacing the pvr. Think I’ll just have to resign myself to always having pvr on to watch tv.

    Cheers
     
  5. Lucid

    Lucid

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    From your description of 90% strength direct vs 100 strength and fluctuating quality via the PVR loopthrough I would lay odds on that the issue is a bit too much amplification from the PVR on top of an already strong aerial signal.

    The effect.of picture breakup is often mistaken for low signal or a broken cable/ tuner. This is the nature of digital TV. Its like walking off a cliff. Everything is great until that final step when it's
    ARGHHHH
    H
    H
    H
    H
    H
    H
    H

    SPLAT

    The answer is to reduce the signal strength getting to the TV tuner. That's done with an attenuator.

    RF attenuators are fairly cheap; £3-£6. Some are a 2" long tubes about the diameter of a coax plug. They connect inline with the coax cable. These ones have fixed values. You buy what you think you might need: 3dB, 6dB, 10dB and so on. If youre already maxed out and over-saturating the tuner then 10dB wouldn't be OTT. 6dB might be enough; 3dB wouldn't help on the most powerful muxes.

    Others attenuators are a box design with a level adjuster. This connects directly to the aerial input on the back of the TV. The coax lead plugs in to the attenuator's socket.

    The value of adjustment ranges from 0 to 20dB. Rotating the adjuster increases or decreases the attenuation. This is probably more useful for a novice.

    https://www.ebay.co.uk/itm/Coax-TV-...-/310160230552?_trksid=p2349624.m46890.l49286

    How to use.
    Set up and view the signal quality display. As you increase the amount of attenuation there'll come a point where the oversaturation falls below the max signal threshold. At this point the quality will start to increase. Continue increasing the attenuation level until the quality reading reaches its maximum level. The signal strength display might not alter even as you approach maximum attenuation. This isn't anything to be concerned about. The metering on TVs isn't entirely accurate or consistent from brand to brand.
     
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  6. Longshanks

    Longshanks

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    Hi again.

    That’s great. Thought it would come down to an attenuator. Funnily enuf, took the pvr back to Asda as only a month old. Got replacement on v off chance it was a specific fault with the loop in connection on the Manhattan. Will connect tomorrow and let you know if it miraculously works. Otherwise will order one of the attenuators. It funny. The old aerial was useless, rotted cable etc. No chance of viable signal with all the splitters. Now it’s too strong.

    Many thanks again.
     
  7. Longshanks

    Longshanks

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    Morning

    Just hooked up new pvr, and same problem immediately kicked in. Will see how the adjustable attenuator works out. Daft question. Will any adjustments permanently effect signal?

    Thanks again.
     
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  8. Lucid

    Lucid

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    "affect" as in reduce the picture quality? No.

    Digital TV works on the principle that once the signal reaches a certain threshold then that's enough. The two elements are signal strength and quality. Of these, Quality is by far and away the most important.

    A simple definition of Quality is the difference between the signal level and any background noise in the aerial system that might corrupt the data bits being received.

    Signal strength is the sum of the background noise and the signal itself. It's possible to have 100% signal strength and still have a lousy picture if the signal is composed of 90% noise + 10% good. This is what you would see when someone tries to amplify a very weak- or poor-quality signal and it still doesn't fix the problem. Conversely, you could have 50% total signal strength composed of say "10% noise and 40% good signal" (correct maths would be 20%:80%) and get a great image.

    What this means is the absolute level of signal strength is unimportant so long as it's enough. The true measure is the proportion of signal to noise: The Signal to Noise ratio (SNR). Reducing (attenuating) the signal won't improve the SNR. It can only be either maintained or reduced. Passive splitting maintains the SNR, and so does passive attenuation.

    Follow the instructions I gave about reducing the signal level and watching the Quality measurement increase.


    Incidentally, if you found these and any other posts on DIYNot helpful to you then click on the Thanks button for each to make your appreciation count. You'll find the Thanks button will appear when you hover your mouse pointer over Multi-quote Quote. (y)
     
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  9. Longshanks

    Longshanks

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    EffectNo meant affect as in influence etc.

    All I was asking was would the signal return to normal, albeit too much for the tv with the pvr chucked in, once the attenuator is withdrawn?

    Thanks
     
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  11. Lucid

    Lucid

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    The attenuator is a permanent addition. Without it in place the signal amplitude will return to its current level. Keep it in place to retain the benefit of the reduction.
     
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  12. Longshanks

    Longshanks

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    Thanks again. Meant if circumstances change, moved pvr to a different location, get a newer TV that doesn’t get the same jolt from the strong signal etc.
     
  13. Longshanks

    Longshanks

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    Update

    Still waiting for attenuator to arrive. Really weird now. The TV situation has deteriorated dramatically. Now, even with external aerial plugged directly into tv, no signal received. Try to tune and no channels found. With aerial plugged into pvr, all channels available and good quality. Also checked upstairs tv (also fed by aerial splitter in loft), and that’s working fine.

    Has it been known for the “too much signa” issue to fry the aerial socket or some linked circuit in the tv? Is that a feasible hypothesis? (It was fine yesterday, when I was trying different connections, taking pvr out of the equation.

    How very bizarre.

    Any expertise here would be much appreciated.

    Thank you.
     
  14. Lucid

    Lucid

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    Broken coax cable.
     
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  15. Longshanks

    Longshanks

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    The coax is fine. It provides a good strong signal for the pvr.
     
  16. Lucid

    Lucid

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    No. To the TV.

    Bearing in mind we aren't there in your room and so only have your descriptions to work from; you're saying you've now lost all signal on the TV via RF (or at least that's how it reads), and this has happened after lots of activity unplugging cables. To add to this, it appears that your PVR-to-TV RF coax is store-bought pre-made Belkin and A.N.Other coax fly lead which presumably means they have moulded plastic-covered connector ends. This covers the cable-to-pin joint which is known to be a weak point in similarly-constructed factory-made cables. The joint breaks, but since the whole think is shrouded in moulded plastic it's impossible to inspect the joint.

    To recap then
    • There's a TV signal elsewhere in the house - so the aerial is okay (and it's a recent install anyway)
    • There's a TV signal at the PVR - so the feeder to the room is okay
    • There's a TV picture on the Pana TV via HDMI - so the TV works, at least via HDMI i.e. the TV is not broken
    • The aerial signal is not amplified - so it's not massively overpowering the tuner input on the TV
    • The aerial signal is passively split to feed the PVR - the quality is preserved, it's just 3-3.5dB lower than would be the case with a direct aerial connection
    • The signal reception at the PVR is fine - and so the level is within an acceptable range for at least that tuner which proves that it's not massively over-powerful
    • There's a problem with the TV RF signal but only when it is connected via a Manhattan PVR loop-through - we know that the loop-through connection on PVRs often includes some amplification
    • There's a problem that reads like too much signal at the RF socket on the Pana - your own research points to the same, and Manhattan tech support have offered that as a potential answer too
    • Changing the Manhattan PVR hasn't cured the issue - so it's not a rogue PVR issue
    • Testing so far appears to rule out HDMI-to-coax-flylead interference
    • Bypassing the PVR and connecting the PVR feeder to the Belkin (or other?) cable results in the TV reporting 100% Q and 90% S - so the TV tuner wasn't oversaturated at the point this test was made i.e. the signal was within an acceptable range for the TV tuner
    • When your TV picture breaks up you noticed that Strength is 100% but Quality falls dramatically - this is a classic symptom of a TV tuner getting too much signal
    • Subject to the local transmitter, some channel muxes are stronger than others, particularly the BBC and main commercial ITV muxes grouped under the PSB designation - this can explain why the issue isn't present all of the time
    • You've ordered a variable attenuator as suggested in my previous advice, but it hasn't yet arrived, and now the situation has changed; you've lost all signal to the TV - this has happened after presumably nothing else in the system has been swapped/added/removed/changed other than a period of cable connection testing?
    • Moulded flyleads are known to be a weak spot since they don't stand up well to disconnect/reconnect activity - a break in the pin-to-cable union would result in partial or total signal loss
    • You're looking for complex solutions without first ruling out the simple stuff
    I haven't yet come across a situation where a TV tuner has been destroyed by an excess of signal where it's not massively over-amplified. The nature of digital TV is that there's a knife-edge change from working to not-working signal condition, and this goes as much for an excess of signal as for too little. I wouldn't rule out a TV fault, but I would certainly eliminate the simpler causes first before condemning what might be a a perfectly fine TV to replacement. A £5 variable attenuator is cheaper than a new TV, and particularly when there's no guarantee that a new TV would fix the problem

    It appears you have an alternative coax flylead. I would try that first if I were you. If possible, I would also try moving the TV to a position where I could try the signal direct from the feeder in to the room without the use of additional flyleads. In the end though it's up to you. If you're hankering for an excuse to buy a new TV then go pull the trigger.
     
    Last edited: 11 Jun 2021
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  17. Longshanks

    Longshanks

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    Hi again

    Thanks for another comprehensive response. All your assumptions in the bullets are correct, save one. I was saying I’d already connected the tv to the direct feed. The “no signal” message on the tv was generated in this position. I originally thought it was TV, as pvr working fine and receiving all channels when connected to same feed. However, I’ve now tried another tv in the same position, and the “no signal” problem persists. I think you’re right and it’s the coax. Just weird that it kicked in suddenly when tv was fine when previously connected directly to the aerial feed. When the aerial was fitted, the guy had to lay additional coax down outside of wall to enter the lounge. He then fitted what looks like a mini connection box screwed into the skirting board, which has the outside cable entering on one side and the existing internal long coax plugged into the the other side. This then runs along the wall approx 15m to feed pvr/tv in conservatory. It’s v evident that the connector on the internal coax seems to be v loose when plugged in. (Have tried a few, gingerly connecting and removing) I’ve now phoned aerial firm, and they’re coming back to take a look.

    Will provide update next week.

    (Also strange that pvr still functions, but guess that’s got much better tuner, needs less signal?)

    Thanks again.
     
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