Help. Signal loss on 101 between 10-5 PM

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SatelliteJoe

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Jan 27, 2009
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Texas
Hello all,

I have been installing satellites commercially for about 15 years and I have come across a problem in the last few weeks I have never encountered before. I was hoping that some of the folks here might have some suggestions.

First I am running a Prodelin Dual Dish system similar to those you would find in Alaska or Hawaii. This one is in Southern Texas on the Mexican border. Here is a picture of a 101 satellite similar to the one I am having issues with.

Shutterfly

When we initially installed these dishes we had no trouble at all. The site had an older 101 dish that we replaced with this one. Since then they have complained that they lose all "premium channels" during the hours of 10-5 PM Meaning all of the channels coming from 101 since the locals come from 119. The reason for the upgraded dishes was to keep the site from losing local channels during the analog to HD conversion since they were on antenna for locals. I am running a SMATV headend with around 24 receivers on it. There is approximately 150 feet between the satellites and the headend and the downleads are RG11

This site is about 5 hours from where I live so today I got the call that the channels were out again. I drove down here and placed a call about 30 miles from the site. The channels were still out. The minute I walked through the door at 5 PM the channels were back on. I checked the signal strength at the rooftop, and on each receiver and every transponder. Just as the day we installed the dishes they are between 95-100 signal strength. I have checked all fittings, tethering, and nuts and bolts on the dish. At the headend I have checked the multiswitches which appear to be in working order and all of the fittings.

We have had a technician on site a week ago when this was occuring and he tested the signal straight from the downlead before it hit the multiswitches and it had no signal so I am fairly certain it is happening before it reaches the headend.

I have had colleagues offer two plausible theories.

One is that there is a mess of pigeons perching on the feedarm between the LNB and the Disc. At first I considered this but the pigeons would have to be on a tight schedule and constantly perching for a long period of time. With that in mind I have moved that to the far fetched category. There is a large pigeon population and alot of pigeon waste on the roof and the existing dishes but I don't know if I can buy that.

The second is that the LNB has some sort of thermal reaction to the heat. This is more believable however at 5 PM today it was 89 degrees outside and the sun was still shining on the rooftop. This outage seems to be on a set schedule.

I am at a loss and would appreciate any suggestions anyone in the know might have.

Some more information about the site is that there appear to be 3 very large towers in close proximity to the satellite location. To the west there is one cell tower and what appear to be two television towers. I'm not sure if this has any bearing on the situation.

As I mentioned earlier this only started happening when we switched 101 from a .9 meter to a 1.2 meter dish.
 
Very strange indeed! I assume you swapped out the LNB just to eliminate the obvious.

Possible RF interferrence from the nearby broadcast towers? It is not uncommon for some older broadcast stations to cut their output wattage in the evening (when signals generally travel better) - or for some rural (local) radio/TV to only broadcast during limited hours.

You could be getting spectrum bleed over from either a very powerful signal or a transmitter that is is very poorly tuned. The larger dish you installed could have magnified the problem.

May think about trying to monitor an old VHF TV with rabbit ears and an AM radio at the site right around 5PM to see what goes off the air (or cuts power) at that time.

Otherwise, moving the dish to the other side of the roof (or setting up an experimental temp) might help the issue.

Good luck with this - it's a tough gremlin - let us know how you finally resolve.
 
I forgot to mention it is sitting on a white rubber membrane rooftop with 7 foot high white rubber membrane walls.

I stayed overnight and waited for the signal to go out. It went to 0 at about 11 AM.

I went to the rooftop and repeaked the dish during the 10:30- 5:00 window where it has been losing signal.

My best guess is that my installers either installed the dish before 10:30 or after 5:00 and that they were able to get some type of signal bouncing off of the white rubber membrane and into the disc without knowing it. The disc is sitting in a giant white bowl more or less. So that is my theory.

At approx 10:30 -11:00 the sun clears the top of the 7 foot wall and shines down into the "bowl like" area on the rooftop and retreats below the westerly wall at around 5:00 . I'm guessing the direct sunlight was changed the reflective properties of the white walls and rooftop.

Does this sound plausible?

I'm trying to understand how they were able to get signal without pointing it at the actual satellite. I've never experienced indirect signal aquisition before with satellites. Off air antennas yes but not satellites.
 
Actually, I've seen signal bounce before - although that involved a building rather than a roof and involved a strong signal bird (119) - so it isn't unheard of.

I assume that with the realign the issue is resolved?
 
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