Trying to receive NOAAport feed on AMC-2 for campus/radio station,reception weak

[sebenste]

Hello everyone,

A college has a weather program where they use weather data and students/staff prepare forecasts for the campus radio station. They have a 3 meter (10') diameter satellite dish with a Norsat 3120 PLL LNB to pick up the NOAAport NWS data broadcast, so they can have weather data to look at and then plot out. The dish has a few small rust spots on the face, but is in generally very good condition. They are trying to pluck the signal from the AMC-2 bird.

The problem is this: their variable bit error rate (VBER) is 1 x 10 ^ -5 during the day, and 1 x 10 ^ -3 at night, which results in data loss. They have tried:

-Repointing the dish twice with a "bird dog" meter, peaking the signal
-Adjusting the height of the LNB to maximize signal at the dish focus
-Tweaking the polarity
-Ensured excellent connections (RG-6 quad shielded cable, tried 4 different cables and ensured tight connectors/connections)
- Bought a "notch filter"

There is another issue, however. The dish is about 300' away from the 400' tower of the FM radio station at 90.9. They broadcast with 5 kw, and they have a plethora of cell phone and other rented broadcasters on there. No matter what they do or tweak, they can't get it better than that. I suspect all that RF from the adjacent tower is causing interference, as people with 3 meter dishes elsewhere are getting it just fine. The NWS spec says that the dish must be at least 3 meters in size.

I've been trying to help them, but I am out of answers. Outside of cell phone providers, I don't know who else is on the adjacent tower. Anyone have any thoughts/suggestions? Thanks!

 

[Doctor_Technical]

1) Dish might be a bit small, not so much in terms of gain, but more in terms of ability to reject unwanted signal(s) from other birds only 2 degrees away. Some quick research on NOAAport shows one receiver company specifying a 12'-14' dish.

2) Is the dish still in good "shape", meaning has the reflector been dented or is otherwise out-of-round?

3) Have you put a good spectrum analyzer on the output? Do some research on the exact freq. of the downlink carrier (as translated by the LNB), then use the analyzer's peak-hold feature to watch that narrow band. Look for odd carriers coming up at night on top of the desired carrier (see item #1).

A good C-band dish, well-aimed, is pretty immune to terrestrial interference (TI), but TI can come from odd places. I've had issues with arcing in nearby elevator controls, and dirty foreign radars on ships coming up the Mississippi River.

Idea: take a big "swing for the fences". Find someone nearby with a big dish that looks at AMC-2 (cable company? TV station?) and drag as much equipment over there as they will allow, in order to eliminate it as a problem.

 

[sebenste]

Hi DT,

Thanks. Yes, unfortunately, I think the dish is too small, and is picking up the rogue signal from a known entity 2 degrees over with the same polarity. The dish is shallow, which means that, of course, the entire dish is "hot", but can also be picking up the rogue signals coming in from the sides of the dish. And, of course, the signal from the other satellite, which came in with only a very slight nudge to the west.

The dish is still in good shape, and has retained its round shape well. No dents.

We've used a "bird dog" on it and see that the signal is weak, and that there's low grade interference from something (the adjacent bird?). Since NOAport is 1/12 the power of the other video/audio carriers on that bird to prevent splatter on other channels, I think...since it is a multi-channel digital feed on one freq...it makes it harder to get. I think the beamwidth on that dish is 1.7 degrees, and of course, that's cutting it REAL close. I have the same feed on a 3.7 meter dish with a beam of 1.4 degrees...no issues whatsoever.