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Thread: Ku band rain fade

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    Default Ku band rain fade

    Hi
    I currently have 2x 80cm dishes which are perfectly aligned to D2 and IS19, used to watch some live feeds when they pop up. Most of the time when its raining the feeds will drop out, and some even when a few grey clouds are around. If I upgraded to 1.2m, how much more reliable could these feeds be? Could I be guaranteed of them working still when its raining?



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    How long is a piece of string questions.

    The larger the dish, the greater the signal capture, so yes, a 1.2m dish will have greater resistance to rain fade than an 80cm dish, but there's so many variables it's difficult to put an actual figure on it.

    Nothing can be guaranteed.

    Even 15m solid uplink dishes can lose signal in very heavy rain.

    Most feeds are received by networks typically on 5m solid dishes.

    Feed signals are not intended to be received direct to homes and they are a lot weaker in signal strength compared to signals intended to be received DTH.

    Location can also make a huge difference to received signal strength, with some locations requiring a 1.2m dish to receive DTH transmissions.

    1/. So in simple terms, no matter how big a dish you use, there is no guarantee against rain fade, regardless of transmission type, but feeds are typically more prone to signal loss on smaller dishes.

    2/. The best you can do is use the biggest dish you possibly can.

    3/. A commercial-specification single polarity PLL LNB will also add sensitivity, selectivity and stability to received signals.

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    Great, thanks for your reply. I know it will not be guaranteed.

    I was hoping just to get some anecdotal reports saying, "yes I upgraded to a 1 or 1.2m, and it made a big difference" or "no, channels still drop out regularly in the rain"

    Thanks

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    mtv, is there a chart/graph showing the rain attenuation at different frequencies?

    From say 4ghz (C-band) thru 12ghz up to say 35ghz? Which band of frequencies are most susceptible to rain fade?

    thanks in advance
    Last edited by cmangle; 21-12-17 at 10:38 AM.

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    I was in helpless mode a few minutes ago and have since woken up and opened both eyes . . . . !

    Rain/sleet/snow fall starts to affect MW frequencies from 8ghz and up (below 8ghz attenuation is negligible) on up to 100ghz where the attenuation flattens out (maybe decreases a little) but stays constant!

    Rainfall amounts also increase the attenuation . . .




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    Lots of relative info on that site, cmangle, so it should cover your question.

    I don't see a definitive, 'one size fits all' answer, as with anything atmospheric, there are a lot of variables.

    Typically with anything RF related, higher frequencies are generally the ones affected most, although in some instances, higher frequencies work better than lower frequencies.

    Machida, a 1.2m dish will definitely be a big improvement compared to an 80cm dish, but if the rain is very heavy, it may still not be sufficient.

    A lot depends on the power of the transponder and the modulation/encoding method of the signals.

    As per my post above, even very large solid 15 metre dishes have been known to lose signal in torrential rain.

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    On Monday last I lost all signals on both a Foxtel 60cm and the VAST 80cm dish for over 20 minutes during a quite substantial rainfall that had hail mixed in as well.
    Although it was belting down here, I didnt loose either signal until the storm moved further away from me towards the Satellite and I am guessing that when the signal dropped out, the storm was by now several miles/kilometres 'thick' in the signal path from me.
    The storm moved roughly along the same path the signal does from the Satellite, that is about 8 degrees East of North from my location.
    By the same token, the storm had diminished markedly around me for several minutes before the signal on both services was receivable.
    On rare occasions we have lost the signal here with no storms locally but it must have been way up in the atmosphere as the weather reports have said that the areas affected were at least 500~600 kms away from here.
    Several years ago a major storm cell hit Sydney and TOTALY wiped out the UPLINK at Belrose affecting Optus and others.
    If a storm can wipe their massive dishes, what chance have you so I would keep what I have and spend the money on something else.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    Considering the number of Foxtel dish subscribers that are out there it has never been a major issue unlike the NBN. The effect of rain fade is really negligible if the 65cm dish is optimized on C1 at say 11dB MER it usually last for a minute or so as the heavy clouds move on. If you refer to It would have to be the far right on the colour chart to effect the signal.
    Last edited by B52; 21-12-17 at 05:16 PM.

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    Quote Originally Posted by B52 View Post
    Considering the number of Foxtel dish subscribers that are out there it has never been a major issue unlike the NBN. The effect of rain fade is really negligible if the 65cm dish is optimized on C1 at say 11dB MER it usually last for a minute or so as the heavy clouds move on.
    Foxtel utilises high-power transponders intended for direct-to-home reception on small dishes.

    The OP is chasing feeds, which are usually much lower in signal strength, with symbol rates and guard levels typically much more difficult to receive and decode without larger dishes, as those signals are not intended for direct reception to homes, rather, reception is intended by TV networks/distributors, typically on 5m solid dishes, or larger.

    These signals are far more susceptible to rain fade, compared to Foxtel signals.

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    One thing I never thought to check was the Internet which I get via Satellite during that storm.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    Have you considered this solution?



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