My Humax Forum » Freeview HD » HDR FOX T2

Intermittent COM7 and COM8 channels on HDR FOX T2

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    ZenSlo

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    I have had a Humax HDR Fox T2 for several years without any problems.

    Earlier this year I started to get intermittent signal loss on all channels on COM7 and COM8 (most noticeable on BBC News HD and BBC Four HD). All the channels on other multiplexors remain perfect. Assuming that this was an aerial fault I decided to upgrade my old aerial to a more modern one with a mast head pre-amplifier (to reject 4G-800LTE etc.).

    Alas this provided no improvement with COM7 and COM8 (although I do get a stronger signal on all channels). I still get severe interference and/or complete loss of picture for several minutes typically every 15 to 30 minutes. There does not seem to be a pattern to the timing or duration of the signal loss. The signal strength and signal quality (as shown by the Humax on the live TV information at the bottom right) is 8/10 when everything is good and 8/0 when there is signal loss.

    My television (a Samsung UE55H6400) has an aerial feed thru via my Humax and has no problems with COM7 and COM8 even when the Humax says “no signal”. I can reliably switch backwards and forwards between the TV and the Humax (both on say BBC News HD) and get a perfect picture on the TV and “no signal” on the Humax.

    Additional Information.

    Transmitter: My local transmitter is Oxford, using channels 41,44,47,29,37,31 and channels 55,56 for COM7 & COM8 respectively. The transmitter is 36km away. My alternative transmitter is Sandy Heath (43km away) and this also uses 55,56 on COM7 & COM8. I do not see any of the Sandy Heath channels after a re-tune. Oxford is on a Bearing of 219 and Sandy Heath is on 74.

    Aerial: My aerial is a “V10-13L 13 element Yagi aerial Ch21-60 4G-800", my mast head pre-amp is a “V20-27T 1in1out variable masthead 12-27dB, Group T, CH: 21-60".

    Signal Strength/Quality: My Humax gives the following information under “Tuned Multiplex Information.”

    29 538.0 MHz 90% 100% Oxon & Bucks COM4/SDN
    31 554.0 MHz 90% 100% Oxon & Bucks COM6/ARQ
    37 602.0 MHz 86% 100% Oxon & Bucks COM5/ARQ
    41 634.0 MHz 96% 100% Oxon & Bucks PSB1/BBC
    44 658.0 MHz 96% 100% Oxon & Bucks PSB2/D3&4
    47 682.0 MHz 96% 100% Oxon & Bucks PSB3/BBC
    55 746.0 MHz 85% 100% Com78 National COM7/ARQ
    56 754.0 MHz 84% 100% Com78 National COM8/ARQ

    Signal Attenuation: Because my signal strength is so good (and having read replies to similar questions on this Forum) I have tried attenuating my signal between 3 dB and 30 dB. Whilst this produces the expected loss of signal strength it does not cure my problem.

    HDMI Cables: I have tried several different high quality HDMI cables and all the HDMI sockets on my TV. My HDMI cable is not close to my Humax aerial-in cable and the two cables never run together.

    Mains power: I have tried using an external mains filter on the Humax, without effect.

    Humax Tuner: In order to see if the problem was specific to one (of the two) tuners in my Humax I have tried recording a non-COM7 COM8 channel whilst simultaneously watching a COM7 channel. With the same result.

    Humax Firmware: Custom firmware version: 3.12 (build 3965), Humax Version: 1.03.12 (kernel HDR_CFW_3.12), Loader Version: a7.30.

    Other equipment: I have powered down and/or removed all other electronic equipment within several metres of my Humax/TV.

    If anybody has any suggestions what to do next they would be greatly appreciated.

    Stephen
    (Milton Keynes)

    | Tue 27 Nov 2018 22:36:29 #1 |
  2. Trev

    Trev

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    Can't help, as you seem to have tried most everything I could think of, but I admire the comprehensive description of the problem and the inclusion of all tests carried out including transmitter and MUXs etc. If only all posters with problems would do the same.

    | Wed 28 Nov 2018 0:33:22 #2 |
  3. grahamlthompson

    grahamlthompson

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    COM 7 and 8 from your transmitter and Sandy Heath are using a SFN - Single Frequency Network, SFN's use a guard interval to minimise co-channel interference, Inevitably there will be areas where the guard interval doesn't eliminate the issue. Some adjustment of the intervals may help,

    http://www.telecomabc.com/s/sfn.html

    As this issue is down to the 800MHz clearance Digital UK should be able to help

    http://www.digitaluk.co.uk/

    | Wed 28 Nov 2018 10:50:23 #3 |
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    ZenSlo

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    Thanks for the SFN information.

    I was aware of the possibility of “interference” from Sandy Heath however if I understand SFN correctly this should reduce the chance of c-channel interference and that coupled with the bearing of the two transmitters (145 degrees apart) and the directionality of my aerial seems to argue against this as an explanation. Although I note that the relevant Sandy Heath transmitter is 57kW whereas the Oxford one is only 13kW.

    The fact that my TV (and that of my neighbours) seem to be immune to this problem makes me think there is something more specifically related to my Humax involved. But I have no idea what!

    Given that the problem seems to me to be Humax specific I doubt that Digital UK would (or indeed should) be able to help.

    | Wed 28 Nov 2018 13:41:26 #4 |
  5. grahamlthompson

    grahamlthompson

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    ZenSlo - 8 minutes ago  » 
    Thanks for the SFN information.
    I was aware of the possibility of “interference” from Sandy Heath however if I understand SFN correctly this should reduce the chance of c-channel interference and that coupled with the bearing of the two transmitters (145 degrees apart) and the directionality of my aerial seems to argue against this as an explanation. Although I note that the relevant Sandy Heath transmitter is 57kW whereas the Oxford one is only 13kW.
    The fact that my TV (and that of my neighbours) seem to be immune to this problem makes me think there is something more specifically related to my Humax involved. But I have no idea what!
    Given that the problem seems to me to be Humax specific I doubt that Digital UK would (or indeed should) be able to help.

    I would take the amplifier out. The FVP-Boxes and the HDR-FOx-T2 do have sensitive tuners - I need to to attenuate to around 60% to get solid reception from Lark Stoke which is also a SFN Using My 5000T and Using My two HDR-FOX-T2 boxes.

    | Wed 28 Nov 2018 13:52:55 #5 |
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    ZenSlo

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    Having read that there was a possibility of my problem being caused by too strong a signal I bought a collection of attenuators 3dB, 2 x 6dB and variable 0 to 20dB. Unfortunately I could not find any combination of attenuation that improved my problem, I was however able to reduce my signal strength to the point where all channels became intermittent.

    | Thu 29 Nov 2018 16:32:50 #6 |
  7. grahamlthompson

    grahamlthompson

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    ZenSlo - 2 minutes ago  » 
    Having read that there was a possibility of my problem being caused by too strong a signal I bought a collection of attenuators 3dB, 2 x 6dB and variable 0 to 20dB. Unfortunately I could not find any combination of attenuation that improved my problem, I was however able to reduce my signal strength to the point where all channels became intermittent.

    If the signal is being clipped by the masthead amp. Then the horse has already bolted, you can't replace the signal distortion after it was created.

    As I said take it out of the circuit. You shouldn't need it. A design with built in attenuation would have been much better.

    https://blusas.co.uk/mho.php?loc=https://www.amazon.co.uk/Vision-V20-4260L-Masthead-Amplifier-Booster/dp/B00MEPIUUG/ref=sr_1_1?ie=UTF8&tag=blusas008-21&qid=1543505945&sr=8-1&keywords=vision+masthead+amplifier

    | Thu 29 Nov 2018 16:37:30 #7 |
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    ZenSlo

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    Unfortunately because it is a masthead pre-amplifier it is difficult to remove it without climbing up my mast.

    Note that exactly the same problem was present with my old aerial which did not have a masthead pre-amplifier (that is why I fitted the new aerial in the first place!).

    Whilst I accept the possibility that the masthead pre-amplifier is “clipping” the signal this seems improbable given that it is a digital signal, my TV can reliably process it and the problem occurs on the channels with the weakest, rather than the strongest signal.

    I don’t understand your suggestion that a masthead pre-amplifier with “built in attenuation” would be a good idea? The one you have linked to seems identical to the one I have except it has a four way splitter after the amplifier (and therefore after any amplifier induced “clipping”).

    | Thu 29 Nov 2018 18:20:51 #8 |
  9. grahamlthompson

    grahamlthompson

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    ZenSlo - 5 minutes ago  » 
    Unfortunately because it is a masthead pre-amplifier it is difficult to remove it without climbing up my mast.
    Note that exactly the same problem was present with my old aerial which did not have a masthead pre-amplifier (that is why I fitted the new aerial in the first place!).
    Whilst I accept the possibility that the masthead pre-amplifier is “clipping” the signal this seems improbable given that it is a digital signal, my TV can reliably process it and the problem occurs on the channels with the weakest, rather than the strongest signal.
    I don’t understand your suggestion that a masthead pre-amplifier with “built in attenuation” would be a good idea? The one you have linked to seems identical to the one I have except it has a four way splitter after the amplifier (and therefore after any amplifier induced “clipping”).

    It's not a digital signal. It's a analogue UHF sinusoidal carrier that is modulated with digital information.

    That's why the term digital aerial is complete rubbish. An aerial is designed to receive a analogue carrier in a specific band of frequencies. If the carrier is clipped the signal is distorted.

    The single attenuator is before the splitter input.

    The four way splitter itself attenuates the signal. Digital amplifiers are very very rare. All the ones you have will be analogue.

    | Thu 29 Nov 2018 18:32:43 #9 |
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    ZenSlo

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    I am aware that the UHF signal is analog at the masthead.
    I am aware that the term “digital aerial” (which I did not use) is meaningless.

    You have made two suggestions for the cause of my specific problem (thank you).

    Your first suggestion was that the aerial signal to my Humax was too strong. I think this is improbable given that with my old aerial (with no masthead amplifier) my signal strength/quality (as measured by my Humax) was 5/10 on COM7 & COM8 and I had the problem.

    Your second suggestion was that by using a masthead amplifier I was distorting the signal by “clipping” it in a way that produced exactly the same problem I was having with my old (un-amplified) aerial. Again I find that improbable.

    Both of your suggestion fail to take into account the fact that my TV can display a perfect picture on the same signal that my Humax claims to be “no signal”.

    Does anybody else have any suggestions?

    | Thu 29 Nov 2018 21:25:08 #10 |

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