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Signal levels of Sky in Spain

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#1
Hi, I did some testing into the receptcion of Sky in my area a while ago ... I changed servers and the site is now back online

Basically it demonstrates that the Sky's signal shits trougth the day ... that renders the reception of some channels impossible some times in the day....

The site is at _http://www.videoacustic.com/sferrairo/skyspain/

I'm still searching for info on why that happens .... people have comed forward with answers, but to me they are not true ....

What some have told me:

That is because the sun:
Not true, because you have peaks and lows indepent of the sun and diferents satellite by satellite

That is because atmosferic condition:
Same as above

That is because shifts on the satellites:
Not true, because that happens always at the same time and it is different satellite by satellite

So, why the signals sifths ? ....

I really don't know and I will like that some one will came forward with a reasonable explanation

Salva
 

dishdoctor

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#2
I think it may be due to the transmiting power available from the onboard batteries or solar panels when extra chanels start transmiting at mid-day or later,or movie chanels start later in the day and use more power to transmit higher quality signals,but if any of the above dont apply it must be due to atmospheric conditions caused by the eec fridge mountain.......Brian
 

Channel Hopper

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#3
Sky's signal shits trougth the day

Classic !

I dont believe that the Sky signal will be variable through simply one cause

Reception loss will be made up of the following (in order of magnitude)

1) Dish size - proven by the article

2) Atmospherics, actually the thermal noise generated around the reception equipment , which will swamp the signal with unwanted interference, and cause the receiver hardship to identify the real channel information. The LNB will bake in the sun if the dish is of solid type, especially if its white

3) Receiver sensitivity, linked with 1), however again the temperature of the unit during daytime operation will cause a difference in recption characteristics unless kept stable with a fridge unit

4) Satellite transponder power deviation, Sky/Astra/Eutelsat can turn down the signal as and when required, this may be down to the programme content (affecting individual channels), territorial license agreements (complete transponder for movie PPV), and satellite power fluctuations (complete bird)

5) - Pointing errors, in a hot country the dish components - mainly the reflector, will distort as a result of the heat, altering the gain by changing focus, however the post, elevation and maybe alignment will change because of the different expansion rates

6) Local effects - beach towels hanging out in front to dry, swarms of flies, plagues of locusts, etc etc
 

rolfw

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#4
RE: Point 3 CH, perhaps the fridge mountain could go some way to solving this.
 
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#5
C'mon boys.....

I'm a engenieer for a number of years and I've thougth an all that ... the reason that I've put this forward is to compare the levels trougth the day to see if everybody is seeing the same in all the "fringe" areas.

! It is NOT ¡ Wheather, ¡ It is NOT ¡ Sun, ¡ It is NOT Atmosferic perturbation ¡ ...

If you think that is one af the above ... how on earth the signal levels shifths the same all the days of the year at exactly the same time ... it does not matter if its cloudy, sunny, wathever.

Pls let people that is seeing this problem in the fringe areas of astra 2 an let them come forward with their experiences

Again, think abt that .... before telling anything ... challenge it with the fact that it always happen at the same time ... all the days of the year ...

As well ... I've check all that with many installations in my area .... so it is not something with my installation

Bye
 

Channel Hopper

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#6
I thought I had explained the atmospheric in terms of thermal and therefore temperature variation relatively well. Nothing to do with clouds or humidity or ionisation of the lower atmosphere etc etc.

The reason it may differ slightly is due to the ground maybe heating up earlier than the sky, the sky heating up slower then the dish surface, etc etc

However my initial conclusion was that it is a combination of all of the variables, and so many individual records have to be made of the parts and how they vary in performance so a isolated lab test is a start.

Anyhow a subject worthy of more testing, and sferrairo wishes to place the full expenses for the ten day excursion to sunny Spain in my account, I will gladly write a full report of my findings
 

zansi

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#7
As a result of this thread, I have booked a 14 day break to Albufiera on the Algarve which is a "edge of footprint situation"

Using a Panasonic TU-DSB 20 with a 1.3m dish & .6db MTI lnb.

Will post my finding on my return.O-Ha
 

PoloMint

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#8
The satellites are not fixed in an exact, stationary, area of space they are placed in a ‘box’ of space 50-75KM in diameter. The satellites are ‘allowed’ to move around within this box without them considered have moved (ie still called stationary). From within the central part of the footprint you would be hard pushed to notice any difference in signal wherever the satellite is within its box. On the edge of the footprint it makes a bigger difference. By not keeping the satellites exactly fixes it saves money, keeping the satellites at exactly the same position would not only be difficult to manage, but require a lot more fuel.

The satellites also rotate twice daily (morning and evening) to maximise the amount of the sun’s rays hitting the solar panels, again this movement keeps the satellites within their box, but if you are on the edge when the rotate you could be off the edge, then back on the edge when they rotate back.
 

dishdoctor

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#9
These movements within the "box" must be largely random movements and could not explain signal loss on some chanels at exactly the same times every day,but the rotation,if at the same time every day may be the cause,but unlikely.In my opinion,for what is is worth,the signal weakness in fringe areas is caused by transponder switching to accomodate power requirements.....Brian
 

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#10
The satellite provider would be ensuring that the steerable antennas on the satellite were pointing at the centre location of the footprint to the best of their ability, which lowers the chances of it being satellite movement within the limitations of the orbital position.

Each satellite has a tracking beacon with fixed frequency, and the ground station has (usually) upwards of eight metre antennas for telemetry purposes, the changes on position from an engineer at the site is quite easy to notice, usually to a movement of under 2kms.

The provider is also fighting to save fuel on the satellite and just like knocking a meteor off a collision with Earth, its better to deflect it sooner, with less fuel, rather than later. The telemetry algorithms will be programmed with the most economical thruster programme to ensure the longevity of the satellite is maintained.

One thing I had not considered however would be the distance of the satellite to the Earth which may also change by a number of kilometers before being detected, (the telemetry station having to use doppler shift of signal to measure this if there is only one station doing the observations). With a fixed focal point antenna on board it would be feasible to assume the actual footprint of the satellite increases and decreases in size with this movement, and so any reception on a fringe area
fringe areas have signal variations on a daily (or twice daily) basis.

I will have to look at the angles of dangle to see if this variation of height affects the fringe areas to a degree enough to be noticed by us amateurs. Thanks to Polomints hypothesis I have another late night using beermat technology, globe and protractor to look forward to.
 
P

pmcmill

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#11
Hi,
Being in Alicante I know first hand about this problem . I posted it in another forum last year and the asnswer I got was this :
"The 2pm-6pm may be the time when routine checks are done which result in a change of position" .
It sounded right to me so I bought it . However this thread is interesting for me and I'll be glad to hear what the final verdict is .
Paul
 

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#12
An evening of peering through the bottom of a number of ale bottles (why do they make them hold so little !) has come up with the following
(pay attention at the back - I shall say this only once )

Taking the difference of apogee v perigee as a possibility of altering fringe power levels to an extent where they are noticed by a ground observer, I have assumed the satellite is controllable to a limit of 80kms. On a satellite such as Astra 2B, running it through the abacus on a footprint of diameter 1600kms means a variation in edge of similar signal of about 45kms, and a difference in area of signal just under 97% of it at perigee.

As one can see from the published footprint for Astra 2B
http://www.ses-astra.com/satellites/footprints_new.php?value=4&sat=13


there is an area of signal that covers Spain and so the fall off in signal, (and therefore dish size ) can be taken as factual reports from Astra and backed up elsewhere in this forum.

Since the fall off is quite dramatic on the footprint above, it is logical to assume that locations further away experience an equal or greater slope of signal to the publicised figures. For arguments sake I will take it as equal which would be the more optomistic but less argumentative case.

The footprint map shows different illuminated areas relating to different dish sizes of 50, 60, 75, 90, 1.2 and so on. These last two are good to highlight as there is an approximate increase in receiving capability of 100% between them(an increase of twice the diameter leads to approximately 4 times the gain).

On the part that shows Spain an approximate distance drawn between the innermost and outermost contour (ie 50cms to 1.2m or 5.6 times the power receivable) is 400kms

Again from the map it is reasonable to assume the signal area contracted by approximately 45 kms lowers the signal at the outer edge (using the above paragraph figures) to a little under half as a direct result of the satellite movement as orbital height difference.

I can conclude therefore that this movement will have a dramatic effect on fringe viewing of this group of satellites (and may go someway of explaining why the Sirius Group at 5E is such a bugger for people to receive in the UK when South of Watford)

More interesting is that the centre of any footprint will actually notice a 3% increase in signal when reaching perigee as the area of footprint is more concentrated at this point, but thats another story.

I thank you.
 

rolfw

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#14
Now you've sorted that one out CH, can you investigate why my toast always falls sticky side down.
 

Channel Hopper

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#15
Thats easy, its called SODs Law.

Normally the attractive properties of marmalade on the toast are in opposite polarity to the properties of hairy carpets, and as opposite polarities attract, the more sticky the marmalade and the hairier the carpet.......... the greater chance they will come into contact.

Further enhancement of the above is obtained by making involutary connection between one leg and a stationary object when moving between kitchen and lounge, such as sleeping cat, motorcycle parts or open tool box, guranteed when conditions have been optimised the night before by active embibement.