Astra 2E & 2F: Sidelobes, Nulls and Spots

[gambit]

. . . However, the main issue I am waiting to see answered is if 2E will still deliver the same blank spot over North East Spain as 2F. To me that dull spot seems very odd especially as further north and even south the signal rises again quite steeply. Is that null area due to something physical on the transmitting antenna - such as a small imperfection or a mark or spot of space dust - or even by design? From the published footprints it seemed that the signal should have gained strength as you move north from southern Spain - which it does through the Costa Blanca and north of Valencia but then suddenly drops off towards Barcelona beore picking up again towards the French border . . .

Apologies if this is off topic, although I guess that joddle's point relates to the framework within which the 2E test data for fringe reception are interpreted.

I have, perhaps mistakenly, believed that the 'blank spot' over North East Spain (Barcelona) and similar regions of low signal are null points between the side lobes - a feature of all satellite dish transmissions. Is it not correct that Barcelona lies on the first null of the 2F UK spot beam, Valencia on the first side-lobe and then south west Spain on or near the second null?

AFAIK the pattern of these side-lobes is determined mainly by the diameter of the transmitting antenna and, given that both the 2E and 2F dishes are the same size, that the side-lobes will be in essentially the same position.

I understood that the similar Astra 2D 'blank spot' around Valencia resulted from the first null from the smaller 2D UK spot dish.

 

[Lazarus]

Apologies if this is off topic, although I guess that joddle's point relates to the framework within which the 2E test data for fringe reception are interpreted.

I have, perhaps mistakenly, believed that the 'blank spot' over North East Spain (Barcelona) and similar regions of low signal are null points between the side lobes - a feature of all satellite dish transmissions. Is it not correct that Barcelona lies on the first null of the 2F UK spot beam, Valencia on the first side-lobe and then south west Spain on or near the second null?

AFAIK the pattern of these side-lobes is determined mainly by the diameter of the transmitting antenna and, given that both the 2E and 2F dishes are the same size, that the side-lobes will be in essentially the same position.

I understood that the similar Astra 2D 'blank spot' around Valencia resulted from the first null from the smaller 2D UK spot dish.

Interesting input and definitely worthy of note.

Don't worry about a little bit of Off-Topic but closely related stuff: It only becomes a concern if it distracts from the actual Testing Reports and that's a judgement Staff will make as and when

 

[timo_w2s]

I have, perhaps mistakenly, believed that the 'blank spot' over North East Spain (Barcelona) and similar regions of low signal are null points between the side lobes - a feature of all satellite dish transmissions. Is it not correct that Barcelona lies on the first null of the 2F UK spot beam, Valencia on the first side-lobe and then south west Spain on or near the second null?

That was my understanding too, but only from what I've read and learnt last year on various forums - I have no idea if the sources are correct.

 

[davidcmadrid]

Apologies if this is off topic, although I guess that joddle's point relates to the framework within which the 2E test data for fringe reception are interpreted.

I have, perhaps mistakenly, believed that the 'blank spot' over North East Spain (Barcelona) and similar regions of low signal are null points between the side lobes - a feature of all satellite dish transmissions. Is it not correct that Barcelona lies on the first null of the 2F UK spot beam, Valencia on the first side-lobe and then south west Spain on or near the second null?

AFAIK the pattern of these side-lobes is determined mainly by the diameter of the transmitting antenna and, given that both the 2E and 2F dishes are the same size, that the side-lobes will be in essentially the same position.

I understood that the similar Astra 2D 'blank spot' around Valencia resulted from the first null from the smaller 2D UK spot dish.

This is correct , and the lobes and nulls seem sharper with this antenna type with the sharpest lobe being focussed on the UK. They have done some pretty advanced director work for the new series of antennas as they are not smooth ( but subtly dimpled ) surfaces. A side effect of how well they focus the primary lobe is the almost apparent randomness but ultimate sharp dropoff of the side lobes. Remember all energy going into the transmission array will result in a better saturation of the target area if they can " mangle " the sidelobes into being small and pronounced.

As for 2E and similarities with 2F, i have little experience but for me its a waiting game to play the " Astra lottery " either the sidelobes will be kind to me as with 2F or they wont

 

[gambit]

Predicted UK Spot

Here is a predicted UK spot footprint for the 2E /2F sats. The red lines show the 1st, 2nd and 3rd predicted nulls. The side-lobes are between those nulls. I assumed a 2.6m diameter dish.

UK Beam Centred on UK​

The map shows that there is a 1st null in NE Spain (Barcelona?) , the 1st side lobe in Valencia and a 2nd null off the coast of SW Spain/Portugal. The 2nd side-lobe is right over the Canaries just north of the Western Sahara. This pattern corresponds broadly with 2F UK spot reception.

In reality, the 2E/FUK beams may be slightly tighter than the predicted footprint so that the whole pattern is shrunk closer into the beam centre.

 

[Lazarus]

Nice work!

Should give folk something to talk about in the quieter moments of Testing.

 

[M60]

Something else to bear in mind is the effect on potential for adjacent interference from 26E which has affected reception in southern and parts of eastern Europe. This isn't present in the C sub-band used by 2F's spot but will be on 2E's D sub-band spot.

 

[gambit]

Predicted 2E "UK Spot" Shifted 15 degrees East

Following my previous post, I include an attempt at a prediction of the UK spot footprint given the current 43.5 east position. Again, the prediction is based on a 2.6m diameter antenna. The red lines show the 1st, 2nd and 3rd predicted nulls.

​

The map is for a satellite positioned at 43.5 east and assumes that its orientation is the same as for a sat at 28.2 east. Therefore, I have assumed that the longitude of the central spot is shifted 15 degrees east from the UK to about 13.5 east (NE Germany).

The specialists on this forum may be able to collate their measurements of the current 2E transmissions with this map. The 1st null runs down the SW corner of the UK, through France, then follows the west coast of Italy. The 2nd null passes close to Israel. That seems inaccurate given Solly's reception of the UK signal in Tel Aviv (11th Oct).

 

[joddle]

Predicted 2E "UK Spot" Shifted 15 degrees East

Following my previous post, I include an attempt at a prediction of the UK spot footprint given the current 43.5 east position. Again, the prediction is based on a 2.6m diameter antenna. The red lines show the 1st, 2nd and 3rd predicted nulls.

View attachment 59016​

The map is for a satellite positioned at 43.5 east and assumes that its orientation is the same as for a sat at 28.2 east. Therefore, I have assumed that the longitude of the central spot is shifted 15 degrees east from the UK to about 13.5 east (NE Germany).

The specialists on this forum may be able to collate their measurements of the current 2E transmissions with this map. The 1st null runs down the SW corner of the UK, through France, then follows the west coast of Italy. The 2nd null passes close to Israel. That seems inaccurate given Solly's reception of the UK signal in Tel Aviv (11th Oct).

I find this all facinating but also a bit (well a lot) out of my sphere of understanding. Firstly how on earth can you predict the nulls without knowing the exact makup of the transmitting antenna? And secondly, according to the map, if similar to 2F, then why is Southern Spain and Portugal having so many problems when they seem to lie between the nulls at almost at the same point as I am in Valencia - so to me they should be enjoying a good signal from 2F as I do!

 

[gambit]

. . . then why is Southern Spain and Portugal having so many problems when they seem to lie between the nulls at almost at the same point as I am in Valencia!

The 2nd map, "the 2E UK Spot Shifted 15 degrees East", is simply the predicted 2F UK spot footprint but shifted 15 degrees east. You cannot use that map to predict reception in southern Spain once the satellite moves to 28.2 east.

To receive a transmission you have to be well away from a side-lobe. The signal is so weak once you are outside the primary lobe that you have to be almost midway between the nulls at the peak of the side-lobe, as you are in Valencia.

. . . how on earth can you predict the nulls without knowing the exact makup of the transmitting antenna?

I do not know what algorithm was used to compute the footprint. I expect it uses a calculation based on a circular dish. The algorithm must use the physics of diffraction patterns given that the pattern of a central peak and side lobes is a diffraction pattern. The pattern for a circular aperture depends only on the dish diameter and the frequency.

 

[Huevos]

how on earth can you predict the nulls without knowing the exact makup of the transmitting antenna?

You can't. Those maps from the spot beam calculator are for a plain parabolic dish, i.e. a non-shaped beam.

 

[Pride Of Cucamonga]

How do the 2E/2F spot beams compare to 2D? Quite a lot i would imagine.

I read somewhere that 2D wasn't even originally intended for 28.2. But this seems odd if it the beam was fixed and just so happened to cover the uK from 28.2. Unless it was reengineered before launch? Also, was the beam shaped? thanks

 

[Pride Of Cucamonga]

To receive a transmission you have to be well away from a side-lobe. The signal is so weak once you are outside the primary lobe that you have to be almost midway between the nulls at the peak of the side-lobe, as you are in Valencia.
.

The 2E spot beam frequencies are lower than for 2F, which I imagine would make the footprint slightly larger and shift the Barcelona null south somewhat. But then the design may be slightly altered to compensate for this. Either way, i think it's unlikely we'll be so lucky in Valencia. Still, 2F should be suffiicent as i#m mostly interested in the terrestrials so likely can watch other regions or SD versions.

 

[Analoguesat]

How do the 2E/2F spot beams compare to 2D? Quite a lot i would imagine.

I read somewhere that 2D wasn't even originally intended for 28.2. But this seems odd if it the beam was fixed and just so happened to cover the uK from 28.2. Unless it was reengineered before launch? Also, was the beam shaped? thanks

According to this:

http://space.skyrocket.de/doc_sdat/astra-2d.htm

2D ( & the similar 3A) were indeed ordered by SES

The 2D beam was much wider than that of 2E/F/G - it could be received in Cyprus with a 4m dish.

 

[Huevos]

it could be received in Cyprus with a 4m dish.

2.4m in some parts. But those Boeing spinners were just cheap, low power satellites with non shaped beams and a handful of transponders. Didn't even have direct-able solar arrays,

 

[cazhh]

The first null of 2f passes just east of Hamburg. Rostock is already in the sidelobe.

 

[Pride Of Cucamonga]

2.4m in some parts. But those Boeing spinners were just cheap, low power satellites with non shaped beams and a handful of transponders. Didn't even have direct-able solar arrays,

Was 2D's low power the reason for its relatively small footprint? I don't think there was any demand from broadcasters for a UK only beam when it launched.

 

[Steve Steve]

Back around 2001 BBC .itv,etc .....could be recieved here with a sky box,FTV card and a mini dish..!!......then BBC and Greg Dyke (the then boss of bbc)....had a bust up with sky about cost of free to veiw cards....then came 2D ...with its so called "spot beam"....(a 1 metre dish was then needed here).....

 

[davidcmadrid]

Here is a link to a youtube directory on the building of 2F , h ttp://www.youtube.com/watch?v=JWndfhAnsIg . At minute 18:57 the antenna guy talks about beam shaping and you can see the modelling of the irregular antenna shape and the subsequent beam.

 

[Pride Of Cucamonga]

Here is a link to a youtube directory on the building of 2F , h ttp://www.youtube.com/watch?v=JWndfhAnsIg . At minute 18:57 the antenna guy talks about beam shaping and you can see the modelling of the irregular antenna shape and the subsequent beam.

Amazing technology.

Any particular reason they would not use exactly the same shaped UK beam for 2E and 2F? I can't think of any as the satellites are built to same spec.