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Splitters and Rain Fade

Discussion in 'DIRECTV General Discussion' started by WaarrEagle, Oct 13, 2013.

  1. slice1900

    slice1900 Well-Known Member

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    It is physics, there is nothing you can do to stop rain fade when the frequency being used by the HD channels has a wavelength similar in size to raindrops. If they used the frequencies SD uses they could mitigate the problems, as you have observed SD is more resistant to rain fade. But they couldn't do that for all HD channels, there isn't enough bandwidth. More importantly it would require all the SD only customers (there are millions) getting new equipment, so it isn't going to happen anytime soon.

    Customers everywhere have to deal with rain fade, but if you live in an area with more rain you will see it more often. Not much you can do about it unless they give you a 10 meter dish :)
     
  2. carl6

    carl6 Moderator Staff Member DBSTalk Club

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    Seattle rain is light and constant, never severe or intense. As a result you almost never see rain fade in Seattle. In the midwest and gulf coast, you get short periods of intense rain which very much will cause rain fade. Over time, I (in Seattle) may get more total rain fall, but never have rain fade.
     
  3. gov

    gov Legend

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    I had a loss of signal a few years ago on a bright sunshiny day. Went out side to see what was up, and to the south there was a huge thunderhead and sighting up from the dish, I was realized my dish was aimed thru the top of the cloud formation. When I switched to OTA, they were announcing severe weather 10 miles south of my location, including large hail and the usual damaging winds.

    Pretty convincing demonstration. As soon as the cloud moved a ways east, my service came right back on.

    So even heavy precipitation distant from your location can be a problem.
     
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  4. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Realistically there is nothing you can do to "stop" rainfade, but there could be things you could do to reduce it: More gain to offset the attenuation.
    Using the larger 1.2 meter dish increases gain by about 6 dB.
    DirecTV could design an LNB with another 10 dB of gain too.

    With climate change seeming to cause more & stronger storms, an LNB change might be needed soon.
     
  5. longrider

    longrider Well-Known Member DBSTalk Club

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    VOS, your comment made me wonder how much gain could you get (assuming the dish was made) out of a 2 or even 3 meter dish? I dont get enough rain fade to worry about it but I could just imagine a DirecTV Not-So-Slimline dish, Rainfade? What rainfade?? :) :)
     
  6. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    A 3 meter would have about 8 dB more gain over the 1.2 meter, so if the 1.2 has 6 over the slimline, then a 10' dish would have around 14.
    Improving the LNB would be cheaper.
     
  7. peds48

    peds48 Genius. DBSTalk Club

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    I have seen LNBs that goes as high as ~ -20dBs, improving that by 10 would mean the output would be around ~-10dB. this would be kind of "hot" for those folks with a single receiver set up. even by putting an 8 way inline it would be still too hot for the receiver. of course this is not the norm. but a ~25dB LNB is, which would be ~-15dB if it increased by 10dB. and that would be "borderline hot" for those with a single set up even with an 8 way
     
  8. gov

    gov Legend

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    Gain is good, but S/N helps too. As the incoming signal degrades adding gain and noise may not do much for reception.

    Probably don't need to dip an LNB in LN2 . . .


    :coffee
     
  9. slice1900

    slice1900 Well-Known Member

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    But is an LNB that outputs at -20dB any more resistant to rain fade than one that outputs at the standard -28dB (or -30dB or whatever it is) Having a 'hot' LNB is no different from adding an amplifier to a regular one, which isn't going to help in a rain fade situation because once the SNR drops to 0 all you're doing is amplifying noise like gov says. If that was all it took I'd add one of those 28db Sonora amps inline before I split to my SWM16s, and never have any rain fade :)

    I'm sure VOS is correct, and that any changes would have to be made inside the LNB to reduce noise. Right now a SNR of 12 or 13 is considered to be a "signal strength" of 100 by the receiver. If the LNB was improved so instead of maxing out at 13 or so it maxed out at 23, it wouldn't matter whether the LNB output at -20dB or -30dB, you'd have improved protection against rain fade. But I think you'd need more than 10 db of improved SNR to make a significant difference.

    I don't see a lot of rain fade here in the midwest compared to what guys in Florida see (especially this summer with the drought) but the Florida guys report that they can often watch SD when HD fades. When we have a supercell move through signal strength will drop to 0 on all sats, including 101. Basically if I lose signal on HD, there isn't any point to switching to SD because the SD signal will be gone by the time you change channels. I don't know how big of a hit SNR must be taking on the HD sats to do that, but I'm pretty sure 10 db wouldn't even scratch the surface of the improvement you'd need. Perhaps 10 db would be enough to reduce the frequency of rain fade events in Florida since they don't typically have storms as big as a supercell (except for hurricanes ;)) but they have storms big enough to cause some rain fade far more often.

    I assume Directv did a cost/benefit analysis when they designed the Slimline LNB and any improvement that would make a measurable difference in rain fade was very expensive, and any inexpensive improvements made no measurable difference. Maybe if/when they design a new LNB another decade of advancement in electronics will change the tradeoff and make something that previously was too expensive more reasonable to do now.

    I look at it this way. If it were possible to build a LNB that offered a significant benefit and could be sold in volumes of tens of thousands a year for $1000/ea, someone would do it. Sports bars, MDUs, and the wealthy would certainly make the investment. As it is you see people trying to use the Alaska/Hawaii dish, even though it only adds about 6db and any benefit is probably in the mind of the beholder justifying the purchase to himself similar to the "improvement" offered by audiophile speaker cable. The only way you'd know for sure would be if you had a neighbor with the regular dish and you knew both were optimally aligned and saw that he had rain fade on occasions you did not (gaining a few seconds of not faded conditions on either end of a storm is of dubious benefit, IMHO) I don't know exactly what that big dish costs, but if you had to pay someone who knows what they're doing to install it, it is probably not far from $1000.
     
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  10. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    An LNB looks to have: an LNA, the mixer stage, followed by another amp.
    Using an AIM and measuring a few LNBs I had, showed "the hot" LNB had the increased gain come from the second amp, and the LNB with a higher CNR had the lower output level.

    These LNBs are made "very cost effective" [aka cheap] as they need to keep track of costs because of the volume.
    This same "talent" could add either an AGC to the first LNA or use [if they don't now] a log amp LNA.
    The CNR might not increase much as "the noise" is part of the carrier, but the range of the LNB could increase while the output levels don't.

    The current LNB design/specs most likely date back 10 years or so.
    When I was on the west coast, the radar had to show red before I had rainfade, but here in the south east, I have rainfade with barely yellow on the radar.
    "I'd guess" there is a market large enough for an improved LNB and the cost increase wouldn't be that great either.
     
  11. Rich

    Rich DBSTalk Club DBSTalk Club

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    If that would stun you, I could really tell you some stories about installers. And their supervisors. But time is short and I don't feel like venting at the moment. BTW, I'm very happy with our present installation contractors, Multi-Band. They come, they don't understand what I've done and why or how it can work, but they just do whatever I ask them to do. Path of least resistance.

    Rich
     
  12. Rich

    Rich DBSTalk Club DBSTalk Club

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    You want to shudder? The first two installers I got when I switched to HD had previous backgrounds in pest control and had only been on the job for about 3 months. They managed to leave many bugs (shuddering) in my system. Took over two years to correct all their mistakes.

    Rich
     
  13. Rich

    Rich DBSTalk Club DBSTalk Club

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    Some of us have been saying the same thing since the advent of the HRs. Falls on deaf ears.

    Rich
     
  14. Rich

    Rich DBSTalk Club DBSTalk Club

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    Huh. I gotta say, Carl, I've never seen anything about rain fade in Seattle and you've explained it very well. I would have thought the Pacific Northwest would be constantly bothered by rain fade. Learn something new every day.

    Rich
     
  15. Rich

    Rich DBSTalk Club DBSTalk Club

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    VOS has mentioned this many times. It's not the cell over your house, it's the cell as you described it that causes the problems.

    Rich
     
  16. slice1900

    slice1900 Well-Known Member

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    Which is what makes rain fade "solutions" sold by snake oil salesmen that amount to a Rain-X type substance for your dish so laughable. If water on your dish caused rain fade, you'd be able to cause it by spraying your dish with a garden hose!
     
  17. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    While I don't approve of the snake oil solutions, a wet towel over the dish does kill the signal.
    It doesn't take much wet snow on the dish to kill the signal, so anything that helps it slide off "might be" a good thing.
     
  18. slice1900

    slice1900 Well-Known Member

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    But how much of that is the towel and how much is the wet? If leaves can block a signal, I'd think a towel is going to hurt the signal quite a bit on its own. You'd want to use something more likely to be transparent to satellite frequencies so the water content is the only variable - maybe take some plastic bubble wrap and use a syringe to fill the cells with water? Or suspend a thin plexglass container in the signal path and add water a few mm at a time. Even those aren't really the same as rain where you have droplets for miles in the signal path - that's probably not equivalent to a single 10mm layer of water in any way. The sad thing is that Directv has probably done some pretty good tests of this sort of thing, but we'll never know.


    At any rate, I assume you had the wet towel in the signal path? That's not the same thing at all as water droplets on the reflector or the LNB. That would be easy to test, check signals, spray it with water, check again. Perhaps water on the dish has a small effect, but I know that rain itself, no matter how hard, does not unless it is a real downpour (the kind of storms where you get a half inch in 15 minutes) However like others I often see rain fade before the first drop even falls - sometimes when no raindrop ever falls for storms that miss just to the south. If droplets have a measurable impact then a RainX treated dish might make the difference for people who live in areas where they get 'marginal' rain fade. Those of us who typically only see rain fade from supercells probably can't be helped by any means, but fortunately they aren't a regular occurrence, and the fade usually only lasts about 10 or 15 minutes until the wall cloud passes.

    I agree about the wet snow, though I've never personally seen any signal loss from snow in seven winters, not even when I had over an inch of ice buildup on the entire roof from a huge ice storm. There may have been some signal drop, I didn't check, but everything still came in just as well as it did before. Maybe the LNB output enough heat to melt that down, I obviously didn't climb up on an icy roof for a close look at the dish (it faces towards the peak so the inside isn't visible from the ground) When it is truly cold the snow that falls isn't as wet or sticky, so less of an issue for it to collect in/on the dish. If I ever did have problems with snow fade I'd get a dish heater, not something that hopes to make the snow slide off.
     
  19. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    The towel [dry] had almost zero effect.
    For the same reason microwave ovens work, it's the water content that's the issue.
    It isn't so much "the leaf" is it as the water in it.
    Without access to my old lab, last year I had use of an AIM and tried to see how one might improve rainfade.
    A wet towel over the reflector was my starting point. Then I tried several partial covering of the reflector.
    None turned out to work very well as the water simply attenuated too much until it started evaporating.
    Somewhat stumped on how to progress, I found sheets of sandpaper covering the LNB gave me more control.
    With 40 sheets [which was about 1" thick] the CNR dropped 3 dB.
    The outcomes of this was there isn't anything to improve rainfade "after" the LNB.

    RainX and the like, aren't going to do squat as the reflector simply doesn't retain that much water, "unless" it's wet snow.
    I've seen photos of snow inches thick on the dish with reports of no signal problems, which can only be due to very dry snow.
    Sierra snow is called Sierra cement for a good reason, as it's more water than snow.

    If you have heavy storms between the SAT and your dish, the only thing you have any control over is the dish.
    Peaking it for maximum gain, increasing the reflector size, cleaning off any snow, or increasing the gain of the LNB [someday I hope] is it.
     

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