[TomB]

I have a pretty good signal with my current 24" dish, but seem to have a rain fade problem with pretty much any storm (regardless of the severity). There were some posts here and in the HDTivo forum (over on the tivo board) about a 'super dish' that was 36" and helped with the rain fade issue. I know that there are some vendors that sell them for this purpose... Anybody have any experience with this thing and its effectiveness?


Thanks in advance....

 

[AntAltMike]

Roughly, signal gain is proportionate to reflector surface area. A 36" dish has 2-1/4 times (9/4) the surface area of a 24" dish, so it would take about 2-1/4 times the density of rain to degrade the signal to the point at which you experience comparable rain fade symptoms.

 

[Karyk]

I upgraded, I think to a 30" dish, and have not had any rain fade issues since on the major networks. Of course, it rains a lot in Seattle, but not that hard typically, so your experience may be different.


It's been a while, but as I recall, I didn't gain that much more signal going to the largest possible dish, and I was a bit afraid of wind damage issues, so slightly smaller was better in my mind.

 

[HDTVFanAtic]

I have a 90cm dish and no matter what you are told, when you get hard rain - say goodnight.

 

[sregener]

Quote:

Originally Posted by HDTVFanAtic I have a 90cm dish and no matter what you are told, when you get hard rain - say goodnight.

I used to work in the satellite field, and I can tell you that even 8' dishes suffer from rain fade under very heavy rain. Ku just doesn't penetrate through water.

 

[Karyk]

Quote:

Originally Posted by HDTVFanAtic I have a 90cm dish and no matter what you are told, when you get hard rain - say goodnight.

Again, this would depend on location. I believe it can rain a lot harder in Florida than it ever does here.


Also, it can depend on what channel you're watching. The signals for our locals off the spot beams are very strong, so harder to disrupt.


The real question is whether you'll see improvement, and the answer to that is yes, even though it might not stop all potential issues.

 

[AntAltMike]

I was called to service the reception antenna farm at MTA (Muslim Television of America) a couple of years ago, and they claimed they were experiencing rain fade on their 30' Ku dish.


I told them I wouldn't touch it with a ten foot pole. The beam width on that monstrosity is so tight that if I even breathed on it, I might lose the aim completely and never find it again.


There is something called the Crane Rain Model that depicts how often rain reaches certain intensities in different regions of the country, and, combining that with other link information, like EIRP antenna gain and threshold S/N ratio, one can actually calculate the average number of minutes per time interval that one will lose their signal lock due to rain fade. I used to care about such things, like when I was doing some work on National Captioning Institute's Ku reception antennas (Patriot 4.5 meters, and, yes, they do occasionally experience rain fade).


TomB in Texas might never again experience rain fade with a 36" dish, except, perhaps, during a hurricane, whereas HDTVFanAtic, in Florida, would still experience occasional rain fade even with a six foot dish.

 

[AntAltMike]

Here is a LINK to some rain fade information that is newer than the Crane model.

 

[Wendell R. Breland]

Quote:

Originally Posted by TomB There were some posts here and in the HDTivo forum (over on the tivo board) about a 'super dish' that was 36" and helped with the rain fade issue.

Tom, what is your satellite service? If Dish Network® or DirecTV® is this a multi satellite dish (2 or more LNB's)? Are you sure there are no obstructions in the field of view? Is the azimuth and elevation of the dish peaked?


If you give me your latitude and longitude or zip code then I can tell you the day and time (early October) when the sun will be directly behind the satellite(s) so you can check for obstructions.

 

[Karyk]

Quote:

Originally Posted by Wendell R. Breland Is the azimuth and elevation of the dish peaked?

Is that a fancy way of asking if the dish is properly aligned?


If so, it brings up a good point. My installer didn't do a very good job aiming the dish. Still, after aiming it better, I still found some rain fade issues and improvement using a larger dish.

 

[TomB]

Quote:

Originally Posted by Wendell R. Breland Tom, what is your satellite service? If Dish Network® or DirecTV® is this a multi satellite dish (2 or more LNB's)? Are you sure there are no obstructions in the field of view? Is the azimuth and elevation of the dish peaked? If you give me your latitude and longitude or zip code then I can tell you the day and time (early October) when the sun will be directly behind the satellite(s) so you can check for obstructions.

Hi, Wendell. I have DirecTV, and have had a pretty good installer help me with a 3LNB dish (I have the HD DirecTivo). My signals show as pretty good (mostly in the 90's) for most of the transponders. I think that an obstruction would generally cause the normal signal quality to be lower, right? I can have the dish moved to a slightly higher location on my roof, which would guarantee no obstructions, and may do that if I have the larger dish installed. Usually, when I have rain fade, I just switch over to the broadcast locals, which I may be watching anyway (lots of hi-def content in primetime these days) or watch something recorded, but the stinking 'searching for satellite on 1 (or 2)' message stays there anyway and is very annoying.


Thanks for the input.


Oh, I'm zip code 76034 (how would I determine my latitude/longitude?)

 

[Wendell R. Breland]

Quote:

Originally Posted by Karyk Is that a fancy way of asking if the dish is properly aligned?

Sure is!! . But on a serious note, many do not realize how critical the aiming of a satellite dish can be. Most of the consumer devices use data errors to indicate quality levels. I find it much easier to use a satellite meter to peak a dish. I have had only a few moisture vapor/rain fades in 11 years of using the pizza dishes.


At work we used Tektronix spectrum analyzers for dish peaking. A picture of the satellite dishes are in this
AVS Forum thread/post.

 

[the_bear89451]

I think better aiming the dish will help too. Florida and Texas are pretty close to the equator. I would expect very little rain fade.

 

[Wendell R. Breland]

Quote:

Originally Posted by TomB I think that an obstruction would generally cause the normal signal quality to be lower, right?

Tom,


Generally true, however you seem to be having problems that most do not have.

Quote:

Oh, I'm zip code 76034 (how would I determine my latitude/longitude?)

For this purpose the info from the US Census Bureau is good enough. For 76034 the Latitude is 32.89 N, the Longitude is 97.15 W.


For the DirecTV satellite at 101°W:

Azimuth of Satellite: 187.1̊

Elevation of Satellite: 51.5̊

Friday, August 12, 2005 – Sun is 20.3̊ above satellite position at 1:42pm CDT.

Thursday, October 6, 2005 – Sun is 0.0̊ above satellite position at 1:34pm CDT.


For the DirecTV satellite at 110°W:

Azimuth of Satellite: 202.8̊

Elevation of Satellite: 49.3̊

Friday, August 12, 2005 – Sun is 21.3̊ above satellite position at 2:04pm CDT.

Thursday, October 6, 2005 – Sun is 0.0̊ above satellite position at 2:15pm CDT.


For the DirecTV satellite at 119°W:

Azimuth of Satellite: 216.4̊

Elevation of Satellite: 45.1̊

Friday, August 12, 2005 – Sun is 23.3̊ above satellite position at 2:26pm CDT.

Thursday, October 6, 2005 – Sun is 0.0̊ below satellite position at 2:56pm CDT.

Please Note: The Azimuth & Elevation given here can not be used for a multi satellite dish.


For the October 6, 2005 (±3 days) date: At the time listed check to see if any shadows falls on or very close your dish. If so, you need to move it. You need to check for shadows at the 3 times listed.

 

[Karyk]

Quote:

Originally Posted by the_bear89451 I think better aiming the dish will help too. Florida and Texas are pretty close to the equator. I would expect very little rain fade.

Okay, this is just sort of off the top of my head, but I don't really think that matters.


Getting the signal through space and the upper part of the atmosphere is not hard. Getting it through the lower part of the atmosphere is not hard if it's not raining. What's hard is getting it through heavy rain in the lower part of the atmosphere. So it's the density of the rain that would be more important than where your proximity to the equator.

 

[AntAltMike]

The conventional wisdom regarding rain fade is, if a slant angle is low, and if it is raining over a wide area, then the signal tends to go through more rain than it would if aimed more steeply. I had more rain fade problems with my DISH system at 28 degrees elevation than I did with my DirecTV at 42 degrees, but for all I know, I might have been comparing old, single powered transponders (120 watts, I believe) with the newer, double powered ones.


There was also some conventional wisdom regarding rain fade on the West Coast, which don't remember, but for some reason, the rain tended to develop more densely on one DBS core satellite's path than on the others (101 deg v 119 deg). Had something to do with the Rocky Mountains, as I recall.

 

[Karyk]

Okay, I guess I could see that, but then again, here in Seattle what heavy rain we get it usually pretty localized.

 

[AntAltMike]

Sonora Design's website used to include a chart that said how much antenna gain was needed to guarantee different percentage of signal availability in different Crane rain zones. At the time they made that chart, single 18" dishes were most common, and I think that an 18" dish would normally develop an S/N ratio of about 13dB from a 120 watt transponder on a clear day (it varies a dB or two depending on where one is located with respect to the boresight), whereas the receivers needed 8dB S/N for a reliable lock.


As I recall, to get something like 99.99% reliability in Florida took a dish that would develop an S/N ratio of about 26dB on a clear day, so to develop an S/N ratio another 13dB greater than an 18" dish normally develops, one would need a dish that has twenty times the reflector surface of an 18" dish, or about 6.5 feet in diameter, to get the same reliability in Florida that you might develop with a 30" diameter reflector in the middle of the United States. But because DirecTV usually uses three satellites in its 101 degree core slot and they are typically about .3 to.4 degrees apart. you can't peak a six foot dish on all three at the same time.


I used to correspond with a guy who is running a bootleg cable company in Venezuela, and he has three HUGE dishes peaked at the three 101 degree satellites (I think his ranged from eight feet to thirteen feet in diameter) and when DirecTV starts slowly migrating a satellite from one side of its slot to the other, he has to continuously repeak his dishes during the move.


I don't think DirecTV allows its commercial MDU operators to use dishes larger than 4 feet in diameter for Sat "A".