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Rain Fade one more time

1558 Views 18 Replies 12 Participants Last post by  tuff bob, 
ub1934
We had some heavy rain come through here in the North East and we (as we always do ) lost 99c/s & 103c/s , 101 , 110 , 119 all will drop to the low 60s to 70s & no loss of picture , without the rain 99 c/s & 103 c/s all read low to mid 90s with some 100s so what else can i check to stop this , Thanks :(
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S
that's pretty much par for the course. i haven't come across anything to stop that. my hd does the same thing and i have high 90's and 100's cross the board.
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davring
Not much, a much larger dish is really the only cure, and I mean a MUCH larger one. Rain can knock out any signal if it is heavy enough.
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E
The only way to increase the fade margin would be to increase the size of the antenna. Consider that the present dish is 3 ft diameter (about), a 6 ft antenna will increase the gain by 6 db, a 12 foot diameter antenna would increase the gain by 12 db.
The present system will have about a 6 to maybe 10 db fade margin. If you changed the antenna to 12 ft (kinda big) you could have about 18 to 22 db fade margin. A heavy rain storm can produce 30+ db fades at Ka frequencies (the new stuff). Thus, even if you went to a very large antenna, it would change the rain fade very little.

I have both 6 ft and 10 ft satellite antennas in by back yard. A couple of years ago I modified the 6 ft to accept a dual LNB for Directv and connected that LNB to a couple of receivers. I also have a 3 LNB Directv antenna with other receivers connected to it. During heavy thunderstorms
the receivers on the 6 ft dish would have signal about 20 seconds longer and return from fade about 20 seconds quicker than the ones connected to the 'normal' antenna.
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66stang351
ub1934 said:
We had some heavy rain come through here in the North East and we (as we always do ) lost 99c/s & 103c/s , 101 , 110 , 119 all will drop to the low 60s to 70s & no loss of picture , without the rain 99 c/s & 103 c/s all read low to mid 90s with some 100s so what else can i check to stop this , Thanks :(
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Move somewhere that it doesn't rain as hard.
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rey_1178
66stang351 said:
Move somewhere that it doesn't rain as hard.
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:D
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J
ub1934 said:
We had some heavy rain come through here in the North East and we (as we always do ) lost 99c/s & 103c/s , 101 , 110 , 119 all will drop to the low 60s to 70s & no loss of picture , without the rain 99 c/s & 103 c/s all read low to mid 90s with some 100s so what else can i check to stop this , Thanks :(
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I had the dark red stuff in Northern Va, was the bottom of the storm you had I think. I only lost for a second around 845, then all was well.

Even during bad storms in South Carolina, the slimline usually only went out no more than 10 minutes, I can live with that.
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davring
A really, REALLY (1/2 mile)tall pole mount:)
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J
What is you converted the LNB to handle 480v instead of 110? :)
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S
eakes said:
The only way to increase the fade margin would be to increase the size of the antenna. Consider that the present dish is 3 ft diameter (about), a 6 ft antenna will increase the gain by 6 db, a 12 foot diameter antenna would increase the gain by 12 db.
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True, doubling the size of the reflector will increase the antenna's gain (and therefore G/T) by 6 dB, but it only works to a point. If you increase the receive dish size too much you reach the point of diminishing returns. A bigger dish also receives more thermal noise. I discovered this a long time ago playing around with link budgets. I kept increasing the size of a Ku-band receive antenna expecting the receive C/N to get greater and greater. It did to a point, but after that point there was no further increase no matter how large you made the dish.

Plus, rain fade isn't completely due to attenuation. There's depolarization as well. No size dish can compensate for that.
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E
Scott in FL said:
True, doubling the size of the reflector will increase the antenna's gain (and therefore G/T) by 6 dB, but it only works to a point. If you increase the receive dish size too much you reach the point of diminishing returns. A bigger dish also receives more thermal noise. I discovered this a long time ago playing around with link budgets. I kept increasing the size of a Ku-band receive antenna expecting the receive C/N to get greater and greater. It did to a point, but after that point there was no further increase no matter how large you made the dish.
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Yes, there are a lot more factors to consider in path design than my very simplistic example. I was just trying to show that increasing antenna size in an attempt to overcome "thunderstorm fade" was a pointless exercise.

In real world design a very critical factor is the max allowable signal into the receiver, or receiver overload point. The BER climbs rapidly if one exceeds that point making upfades an important consideration in path design. In some cases one has to accept a lessor fade margin to avoid an upfade problem.
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dshu82
ub1934 said:
We had some heavy rain come through here in the North East and we (as we always do ) lost 99c/s & 103c/s , 101 , 110 , 119 all will drop to the low 60s to 70s & no loss of picture , without the rain 99 c/s & 103 c/s all read low to mid 90s with some 100s so what else can i check to stop this , Thanks :(
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You state "no loss of picture" which is good, so signal drop should not be a concern.

We get storms down here all summer long, some days lose picture for 5-10 minutes maximum. Had a very bad storm yesterday afternoon and did not lose picture at all......
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davring said:
Not much, a much larger dish is really the only cure, and I mean a MUCH larger one. Rain can knock out any signal if it is heavy enough.
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With Direct's integrated triple LNB for MPEG4, you can't got a larger dish. Nothing else works since their dishes are not standard shapes. Put up a 6 footer with the triple LNB for 99/101/103 and the sigal will be worse.
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davring
FarNorth said:
With Direct's integrated triple LNB for MPEG4, you can't got a larger dish. Nothing else works since their dishes are not standard shapes. Put up a 6 footer with the triple LNB for 99/101/103 and the sigal will be worse.
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Some of the guys here, far more knowledgeable than I, build their own.
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T
How much gain do you think the 1.2m DirecTV dish has over the slimline 5?
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S
tuff bob said:
How much gain do you think the 1.2m DirecTV dish has over the slimline 5?
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What are the dimensions of a Slimline 5? That's an elliptical reflector, correct? That makes estimating its equivalent diameter difficult. But here's the equation:

Gain or loss in dB = 20 log (diameter 1/diameter 2)

Someone else brought up a very important point. Just replacing your reflector with a larger diameter reflector may cause more harm than good. You must install the LNB(s) at the correct focal point.
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T
22.5 in. x 32.5 in.

Obviously by buying the DirecTV 1.2m (Alaska/Hawaii) kit, the lnb should line up nicely with the reflector :)

Now that we only need to see 99-103 in HD-LIL markets, I'm wondering whether the 1.2M kit is worthwhile to cope better with rain fade
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curt8403
tuff bob said:
22.5 in. x 32.5 in.

Obviously by buying the DirecTV 1.2m (Alaska/Hawaii) kit, the lnb should line up nicely with the reflector :)

Now that we only need to see 99-103 in HD-LIL markets, I'm wondering whether the 1.2M kit is worthwhile to cope better with rain fade
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since the 1.2 is used with 110, 101, and 119 sats it would be useless for 99 or 103
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T
curt8403 said:
since the 1.2 is used with 110, 101, and 119 sats it would be useless for 99 or 103
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that's not what doctor j found.

http://www.dbstalk.com/showpost.php?p=1350332&postcount=327
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