Height of Geosynchronous Satellite

[cyberham]

Just for fun, I'm trying to justify to myself why I may have lost signal from 125W.

There are a lot of rain storms in east coast areas of the U.S these days. The signal from 125W originates from the satellite's geosynchronous position above the equator out in the Pacific Ocean and travels over the U.S. to my location in Nova Scotia. To be blocked by these rain storms which are likely relatively close to the Earth's surface, the signal must travel relatively close to the Earth's surface en route to Nova Scotia.

My Google search indicates the geosynchronous height of a satellite is about 35,786 km above the equator. The elevation angle from my dish to this satellite is 11.2 degrees according to Dishpointer. This same source (Dishpointer) says I am 40,457 km from this satellite. When I pull out my high school trigonometry, use 40,457 km as the hypotenuse of the triangle formed between the satellite, my location and the point at the equator directly below the satellite, then calculate 40,457 x (sin 11.2) = 7858 km, this suggests the satellite is only 7858 km above the equator. Something isn't right! Some data must be incorrect.

With an elevation angle of 11.2 degrees, intuitively it seems logical the signal could be blocked by weather to the southwest of my location. I wanted to calculate how far away the weather would have to be and at what height above Earth in order for it to block the signal from 125W. But the math doesn't work out anywhere close. Why?

 

[comfortably_numb]

My understanding was that Ku reception could be influenced by rain at your location and/or rain at the uplink location.

 

[cyberham]

I agree. I'm just looking at one side of the situation right now: the downlink from satellite to me. You would also need to consider the uplink side too for a full evaluation. This is why I guess it's hard to figure accurately if weather is the culprit. But I've learned and I'm not touching my dish as I did in past. The dish hasn't moved. Yet I have zero signal now and haven't had reliable signal for a couple of days.

 

[comfortably_numb]

I agree. I'm just looking at one side of the situation right now: the downlink from satellite to me. You would also need to consider the uplink side too for a full evaluation. This is why I guess it's hard to figure accurately if weather is the culprit. But I've learned and I'm not touching my dish as I did in past. The dish hasn't moved. Yet I have zero signal now and haven't had reliable signal for a couple of days.

This used to happen a lot with feeds on 87. Most of the services on that satellite are located on the eastern seaboard. LPB is especially sensitive to rain in the spring months.

 

[Brct203]

Just for fun, I'm trying to justify to myself why I may have lost signal from 125W.

There are a lot of rain storms in east coast areas of the U.S these days. The signal from 125W originates from the satellite's geosynchronous position above the equator out in the Pacific Ocean and travels over the U.S. to my location in Nova Scotia. To be blocked by these rain storms which are likely relatively close to the Earth's surface, the signal must travel relatively close to the Earth's surface en route to Nova Scotia.

My Google search indicates the geosynchronous height of a satellite is about 35,786 km above the equator. The elevation angle from my dish to this satellite is 11.2 degrees according to Dishpointer. This same source (Dishpointer) says I am 40,457 km from this satellite. When I pull out my high school trigonometry, use 40,457 km as the hypotenuse of the triangle formed between the satellite, my location and the point at the equator directly below the satellite, then calculate 40,457 x (sin 11.2) = 7858 km, this suggests the satellite is only 7858 km above the equator. Something isn't right! Some data must be incorrect.

With an elevation angle of 11.2 degrees, intuitively it seems logical the signal could be blocked by weather to the southwest of my location. I wanted to calculate how far away the weather would have to be and at what height above Earth in order for it to block the signal from 125W. But the math doesn't work out anywhere close. Why?

the problem with your calculation is that the 11 degree angle is not the right one... It's the angle between that hypotenuse and the tangent to the earth surface at your location, and that tangent does not cross anywhere near the point on the equator below the satellite. The trigonometry involved is a lot more complex.

 

[cyberham]

I think I get your point. My explanation would be correct if the Earth was flat. Since the Earth is curved, this is why the tangent at my location is not the tangent at the location below the satellite at the equator.

Sent from my SM-G950W using the SatelliteGuys app!

 

[mdonnelly]

I think that since Nova Scotia is at 55 degrees latitude, you need to add that to your 11.2 for the true elevation.

 

[cyberham]

That is factored in on dishpointer. My latitude is 44.7 N. The true elevation for my dish at this location is 11.2 degrees. I will stop trying to do this trigonometric calculation since I agree with brct203 that it is more complicated than I first considered.


Sent from my SM-G950W using the SatelliteGuys app!

 

[Magic Static]

Complicated for sure when you stop to consider while the earth isn't flat, it's not a perfect sphere either. So now you're doing the math they used to create USALS.

 

[a33]

Well, normal USALS calculations don't take into account that the earth is no sphere, as far as I know.
Nor do they take into account that a good motor setup does not have its rotation axis parallel to the earth's axis, but tilted forward towards the Clarke Belt.

However, the errors due to these points are very small. I'm not quite sure if these errors add up to a greater error, or if they counteract each other, or have maybe completely independant effects. The USALS angles and calculation I understand a bit; the non-spherical earth with consequences (the latitude angle changing, and the earth surface angle changing) I found too big a hurdle for me.

Greetz,
A33

 

[cyberham]

Some good points. My original intent was only to understand "approximately" if the heavy storms would have an effect. We all know they do. I see today even worse storms across Nebraska, Kansas and further south. Yet local weather here is sunny & clear. Makes me wonder if orienting my dish throigh the years may have been futile at times since there simply was no strong signal in my backyard some of those times.

Sent from my SM-G950W using the SatelliteGuys app!

 

[NYDutch]

The bottom line is that the farther the storm is from you, the higher it can be and still block the sat signals.

 

[Brct203]

well, there are many ways storms can affect a satellite transmission.
- the most obvious is heavy rain at the reception site - we are all aware of rain fade at that end, at least for Ku.
- rain fade can also affect the uplink, as was mentioned earlier in the thread
- on both ends, the lower the angle, the more atmosphere the waves have to go through, for the same reason that the sun takes a red tint near the horizon and is not as bright, making it more susceptible to not-local storms.
- wind pushing a dish or shaking a dish can also affect it's aiming accuracy, and with large cheap dishes, can affect the geometry of the dish
- in the case of snow or ice, the added weight on the dish can easily affect it's elevation accuracy ( i see it very much on my C-Band dish)

 

[Titanium]

Add particulates to the mix. Several years ago during a severe wild fire, my LNB sample testing was interrupted by the heavy smoke which severely attenuated the satellite signals.

Solar activity can effect the rf transparency of the ionosphere. Heat will raise the noise floor and reduce the base threshold and also thermal heating of the LNBF will reduce the performance.

RF ducting may introduce temporary interference or refraction. This effect is increased at lower elevation angles.