My Humax Forum » Freesat HD » HDR 1000, 1010, 1100S

Some Channels With No Signal Reception

(36 posts)
  1. REPASSAC

    REPASSAC

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    The LNB is the small thing at the end if the dish arm, most current ones have 4 connections two of which can be connected to a tuner on your Humax receiver unit.

    The receiver controls the LNB electrically which causes the LNB to switch between 4 bands Low and High on both Vertical and Horizontal polarises frequencies.

    Which it is possible for the Humax switching to be faulty, I can not recall a single case of this, against significant numbers of LNB.

    Subject to access, replacing the LNB yourself is easy and inexpensive. Remember to note the skew (Twist) before replacing.

    | Thu 21 Sep 2017 10:26:54 #31 |
  2. grahamlthompson

    grahamlthompson

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    DMB - 1 hour ago  » 
    Thanks Guys (or maybe it's girls) for a prompt response. I am not on a communal system. Forgive me but I don't know what an LNB is. I did most of my electronic engineering before digital and at aged 80 struggling to get to grips with this - but determined to do so. Am I right in thinking it is the Humax box that distinguishes between the H and V channels or is it done somehow on the rooftop dish? Can't see how the latter is possible unless the H and V signals come from different satellites??

    The lnb is the box on the end of the arm on your dish. The dish is a parabolic shape which collects the microwave signals from the group of satellites at 28.2E. This is about 22000mls directly over the equator at 28.2E. At this height the satellite orbits the Earth in the same direction as the Earth spins and in the same period. This means to an observer on the Earth the satellites appear stationary so a fixed dish can be used. The lnb has a waveguide that collects the microwave radiation. The type we use in Europe is a Ku Band Universal device. The frequency is far too high to use coax cable with, so it has to be shifted to a lower frequency. LNB stands for low noise block down converter. Due to the age of the technology the downshift has two options splitting the microwave frequencies into two halves high band and low band. The frequency range coming down the cable is the same for high band (larger downshift) as low band. Technically the frequency range is known as the IF (Intermediate Frequency). The tuner switches the lnb from it's default of low band operation to high band by imposing a 22Khz tone on the coax downlead connecting that tuner to the lnb. In order to squeeze the maximum number of seperate frequencies into the bandwidth each alternate one is alternately polarised horizontally or vertically. Each frequency is transmitted by a transponder with all its channels digitally modulated on the carrier. We refer to each as a transponder in digital satellite (Freeview Digital uses the term Mux (short for multiplex) for the same process).

    The tuner supplies power to the LNB and signals the switch between Horizontal and Vertical by varying the DC power level.

    This is a a quote from the excellent Satcure website

    "A modern "Universal" LNB requires a 22 kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6 GHz ("high band"). Otherwise it uses its 9.75 GHz oscillator.

    Polarisation switching is controlled by DC voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB (although I have run it up to 24 volts, briefly, without damage). A voltage that is too low will prevent the LNB from working correctly.

    This switching voltage, fed up one or more cables, also powers the internal electronics of the LNB. A modern LNb requires 125mA or more."

    Don't worry too much if this is a tad confusing.

    The real message is that unlike an aerial which is a passive device a lnb and it's tuner talk to each other whicj is essentially the reason you can't split a satellite signal without the extra tuner having any control of the lnb segment it's connected to.

    Most Freesat kit is connected to a dish and lnb designed for Sky receivers as because of the millions made they can be bought for very little money (Have a look on E-Bay). Sky type lnbs are available with one, four or 8 outputs. Most will have the four output quad type lnb's fitted.

    If you need more than 8 outputs we then get into the use of multi-switches which is a whole new explanation.

    More reading here

    https://forums.digitalspy.com/post/quote/930633/Comment_28734358

    | Thu 21 Sep 2017 10:31:23 #32 |
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    DMB

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    Ok- thanks for your advice REPASSAC and Graham. I think you can ignore most of my last post because I just googled and found that the LNB is a Low Noise Block down-converter that inter-alia separates H and V channels by tuning to appropriate frequency and creating an intermediate lower frequencyI. Like a superhet radio used to do. I'll get a new LNB fitted.
    I wasn't looking forward to doing a reset and not sure how to do a manual tune either. Hope the new LNR will fix the problem. I may have to come back for help if it doesn't.

    | Thu 21 Sep 2017 11:00:32 #33 |
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    DMB

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    OOPS! I was still typing my last and overlapped with your very helpful and thorough excplanation Graham. It's clear now thanks.

    | Thu 21 Sep 2017 11:06:24 #34 |
  5. grahamlthompson

    grahamlthompson

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    DMB - 21 minutes ago  » 
    OOPS! I was still typing my last and overlapped with your very helpful and thorough excplanation Graham. It's clear now thanks.

    You are correct re the band switching it is the exact same principle as a superhet radio. Slightly off topic but the new Sky-Q system uses a wideband lnb (no band switching) so a single IF range (which overlaps the terrestrial UHF bands) with the standard lnb having only two outputs. One for Horizontal and the other for Vertical so no polarisation switching either. This means with only two cables that a lot of tuners can be used. They simply select the horizontal or vertical input as required.

    | Thu 21 Sep 2017 11:33:54 #35 |
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    DMB

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    Thamks for that. You've inspired to get my ancient brain working and I'll try to learn more. I spent many years in electronic design mostly using discrete components in an analogue world at a time when a chip with >100 transistors was a novelty.

    | Thu 21 Sep 2017 12:55:54 #36 |

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