So what is the real reason for the greater size of dish needed?
Might it be because further north the 'footprint' of signal is more, 'diffuse' on the earth's surface ?(Shine a torch onto a football to see what I mean) Or I might just be talking bollocks ?
One for the pros here. According to this site ...
Satellite Dish Suggested Minimum Sizes https://www.smartaerials.co.uk/blog/what-size-satellite-dish-do-i-need
"The further you‘re away from the satellites in space the weaker the
received signal will be. As the satellites remain in geostationary orbit around the equator the further in the UK north in the UK you are
installing your satellite dish the weaker the received signal will be, meaning that satellites dishes installed in the north of England and satellite usually require a larger dish that those using a comparable
service in the south of England."
I don't dispute the need of the larger dish, but I'm suspicious of the
reason given, not just because it is garble-worded, but more importantly
as follows ...
The radius of earth is about 6,371 km
The radius of the Clarke Belt is 42,164 km
The south coast of England is around 50 degrees N
The border between England & Scotland is around 55 degrees N
There is a nice little triangle solver here: https://www.calculator.net/triangle-calculator.html
Putting the above into it gives us:
South Coast distance to Clarke Belt = 38,380 km https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=50&vz=42164&vb=&angleunits=d&x=62&y=34
Border distance to Clarke Belt = 38,862 km https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=55&vz=42164&vb=&angleunits=d&x=62&y=34
I accept that I haven't allowed for the sats being at 28E rather than
due south, but this is good enough to tell us that, for the two example locations above, the order of magnitude of the difference in distance
from sat to dish is likely to be only around 1%, and, even after
applying the inverse square law, one would think that's not enough to
justify a substantially larger dish?
So what is the real reason for the greater size of dish needed?
On Thu, 05 May 2022 16:53:10 +0100, Mark Carver wrote:
Might it be because further north the 'footprint' of signal is more,
'diffuse' on the earth's surface ?(Shine a torch onto a football to see
what I mean) Or I might just be talking bollocks ?
Doesn't the inverse square law have something to do with it?
On 05/05/2022 15:47, Java Jive wrote:
So what is the real reason for the greater size of dish needed?
I don't know the reason but perhaps
The path through the atmosphere is longer hence greater attenuation of
the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
On 05/05/2022 17:30, alan_m wrote:
On 05/05/2022 15:47, Java Jive wrote:
So what is the real reason for the greater size of dish needed?
I don't know the reason but perhaps
The path through the atmosphere is longer hence greater attenuation of
the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
Except the signal also similarly fades on all edges of the footprint
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
Mark Carver <mark.carver@invalid.invalid> wrote:
On 05/05/2022 17:30, alan_m wrote:Isn’t that just the gain of the tx antenna falling off towards the edges of its beam?
On 05/05/2022 15:47, Java Jive wrote:Except the signal also similarly fades on all edges of the footprint
So what is the real reason for the greater size of dish needed?I don't know the reason but perhaps
The path through the atmosphere is longer hence greater attenuation of
the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
On 05/05/2022 17:42, Tweed wrote:
Mark Carver <mark.carver@invalid.invalid> wrote:Well yes, so I think that's the answer ?
On 05/05/2022 17:30, alan_m wrote:Isn’t that just the gain of the tx antenna falling off towards the edges of
On 05/05/2022 15:47, Java Jive wrote:Except the signal also similarly fades on all edges of the footprint
So what is the real reason for the greater size of dish needed?I don't know the reason but perhaps
The path through the atmosphere is longer hence greater attenuation of >>>> the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to >>>> the horizon is red - the light travels further through the atmosphere.
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
its beam?
On 05/05/2022 17:30, alan_m wrote:
On 05/05/2022 15:47, Java Jive wrote:
So what is the real reason for the greater size of dish needed?
I don't know the reason but perhaps
The path through the atmosphere is longer hence greater attenuation of
the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
Except the signal also similarly fades on all edges of the footprint
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
On 05/05/2022 15:47, Java Jive wrote:
Might it be because further north the 'footprint' of signal is more, >'diffuse' on the earth's surface ?(Shine a torch onto a football to
So what is the real reason for the greater size of dish needed?
see what I mean) Or I might just be talking bollocks ?
So what is the real reason for the greater size of dish needed?
In message <jdia76FclaoU1@mid.individual.net>, Mark Carver <mark.carver@invalid.invalid> writes
On 05/05/2022 15:47, Java Jive wrote:
Might it be because further north the 'footprint' of signal is more,
So what is the real reason for the greater size of dish needed?
'diffuse' on the earth's surface ?(Shine a torch onto a football to
see what I mean) Or I might just be talking bollocks ?
Wouldn't that be counteracted by tilting the dish at the optimum angle
so that the signal still impacts on it at 90 degrees? The suggestion
that it's due to a longer passage through the atmosphere causing more attenuation seems more likely.
On 05/05/2022 17:30, alan_m wrote:
On 05/05/2022 15:47, Java Jive wrote:
So what is the real reason for the greater size of dish needed?
I don't know the reason but perhaps the path through the atmosphere is
longer hence greater attenuation of the signal ????
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
Except the signal also similarly fades on all edges of the footprint
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
Although I'm only replying to this one, I've read all the replies so
far; thanks for them all ...
On 05/05/2022 17:39, Mark Carver wrote:
On 05/05/2022 17:30, alan_m wrote:
On 05/05/2022 15:47, Java Jive wrote:
So what is the real reason for the greater size of dish needed?
I don't know the reason but perhaps the path through the atmosphere is
longer hence greater attenuation of the signal ????
Yes, I'd thought of that as well, and I think that's the most likely explanation, see also below ...
In the SE of England 28.2E the elevation is 25 degrees - in Scotland
its 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
Yes.
Except the signal also similarly fades on all edges of the footprint
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
I don't dispute that the signal fades towards the edge of coverage, but
if you look at the coverage map there, coverage is centred on the
British Isles as a whole, so if the need for a larger dish was due to
fading of the signal towards the edge of coverage, the border area
should be getting a stronger signal than the south coast of England, and therefore a smaller dish should be needed in the borders, and a larger
one on the south coast, whereas reality is the other way round!
I think the argument about the amount of atmosphere the signal has to
travel through is the most convincing so far suggested.
At 10 GHz atmospheric attenuation is 0.02dB per km, propagating
horizontally at sea level.
On 05/05/2022 18:22, Tweed wrote:
At 10 GHz atmospheric attenuation is 0.02dB per km, propagating
horizontally at sea level.
That's only in good weather. Rain causes a lot of attenuation. Whilst
I don't know exactly how much, uplink powers have to be controlled to
avoid overloading transponders when there is no rain, whilst providing
enough signal in rain.
On 05/05/2022 21:09, Java Jive wrote:
I think the argument about the amount of atmosphere the signal has to
travel through is the most convincing so far suggested.
There should be sufficient information here http://www.apsattv.com/techinfo/predicting-out-of-footprint-coverage.htm
to answer your question with facts rather than speculation.
On 05/05/2022 18:22, Tweed wrote:
At 10 GHz atmospheric attenuation is 0.02dB per km, propagating
horizontally at sea level.
That's only in good weather. Rain causes a lot of attenuation. Whilst
I don't know exactly how much, uplink powers have to be controlled to
avoid overloading transponders when there is no rain, whilst providing
enough signal in rain.
There should be sufficient information here http://www.apsattv.com/techinfo/predicting-out-of-footprint-coverage.htmits 20 degrees. Possibly the same reason why a setting sun closer to
the horizon is red - the light travels further through the atmosphere.
Yes.
Except the signal also similarly fades on all edges of the footprint
(which blows my theory out of the water too)
https://en.satexpat.com/coverage/east/28.2/
I don't dispute that the signal fades towards the edge of coverage, but
if you look at the coverage map there, coverage is centred on the British
Isles as a whole, so if the need for a larger dish was due to fading of
the signal towards the edge of coverage, the border area should be
getting a stronger signal than the south coast of England, and therefore
a smaller dish should be needed in the borders, and a larger one on the
south coast, whereas reality is the other way round!
I think the argument about the amount of atmosphere the signal has to
travel through is the most convincing so far suggested.
to answer your question with facts rather than speculation.
One for the pros here. According to this site ...
Satellite Dish Suggested Minimum Sizes https://www.smartaerials.co.uk/blog/what-size-satellite-dish-do-i-need
"The further you’re away from the satellites in space the weaker the received signal will be. As the satellites remain in geostationary orbit around the equator the further in the UK north in the UK you are
installing your satellite dish the weaker the received signal will be, meaning that satellites dishes installed in the north of England and satellite usually require a larger dish that those using a comparable service in the south of England."
I don't dispute the need of the larger dish, but I'm suspicious of the reason given, not just because it is garble-worded, but more importantly
as follows ...
The radius of earth is about 6,371 km
The radius of the Clarke Belt is 42,164 km
The south coast of England is around 50 degrees N
The border between England & Scotland is around 55 degrees N
There is a nice little triangle solver here: https://www.calculator.net/triangle-calculator.html
Putting the above into it gives us:
South Coast distance to Clarke Belt = 38,380 km https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=50&vz=42164&vb=&angleunits=d&x=62&y=34
Border distance to Clarke Belt = 38,862 km https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=55&vz=42164&vb=&angleunits=d&x=62&y=34
I accept that I haven't allowed for the sats being at 28E rather than
due south, but this is good enough to tell us that, for the two example locations above, the order of magnitude of the difference in distance
from sat to dish is likely to be only around 1%, and, even after
applying the inverse square law, one would think that's not enough to justify a substantially larger dish?
So what is the real reason for the greater size of dish needed?
--
Fake news kills!
I may be contacted via the contact address given on my website: www.macfh.co.uk
Is there a reason why they don't want dishes to point vaguely south (or
north in the southern hemisphere), and instead to point vaguely
south-east (for UK)?
On Thursday, 5 May 2022 at 15:47:29 UTC+1, Java Jive wrote:
One for the pros here. According to this site ...
Satellite Dish Suggested Minimum Sizes
https://www.smartaerials.co.uk/blog/what-size-satellite-dish-do-i-need
"The further you’re away from the satellites in space the weaker the
received signal will be. As the satellites remain in geostationary orbit
around the equator the further in the UK north in the UK you are
installing your satellite dish the weaker the received signal will be,
meaning that satellites dishes installed in the north of England and
satellite usually require a larger dish that those using a comparable
service in the south of England."
I don't dispute the need of the larger dish, but I'm suspicious of the
reason given, not just because it is garble-worded, but more importantly
as follows ...
The radius of earth is about 6,371 km
The radius of the Clarke Belt is 42,164 km
The south coast of England is around 50 degrees N
The border between England & Scotland is around 55 degrees N
There is a nice little triangle solver here:
https://www.calculator.net/triangle-calculator.html
Putting the above into it gives us:
South Coast distance to Clarke Belt = 38,380 km
https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=50&vz=42164&vb=&angleunits=d&x=62&y=34
Border distance to Clarke Belt = 38,862 km
https://www.calculator.net/triangle-calculator.html?vc=&vx=6371&vy=&va=55&vz=42164&vb=&angleunits=d&x=62&y=34
I accept that I haven't allowed for the sats being at 28E rather than
due south, but this is good enough to tell us that, for the two example
locations above, the order of magnitude of the difference in distance
from sat to dish is likely to be only around 1%, and, even after
applying the inverse square law, one would think that's not enough to
justify a substantially larger dish?
So what is the real reason for the greater size of dish needed?
--
There are several real reasons: -
1. Further away, although not that much.
2. Beam centre will probably be aimed at southern England, so in Scotland you will be off the narrow beam with a weaker signal. (works the other way too, you CAN pick up UK channels in Spain, but you need a BIG dish).
3. More atmospheric attenuation - more signal lost passing through more atmosphere.
On 06/05/2022 13:02, NY wrote:
Is there a reason why they don't want dishes to point vaguely south (or north in the southern hemisphere), and instead to point vaguelyDue South would put the Sun in the centre of the receiver main lobe
south-east (for UK)?
twice a year. The noise temperate of of the Sun is about 6,500K,
whereas a good LNB might have a noise temperature of a few tens of K,
and space could be as low as about 3K.
Being out on the limb of Europe might be another factor.
There are several real reasons: -
1. Further away, although not that much.No, sorry, but this just cannot be the explanation. Consider ...
The calculation still quoted above for a satellite due south is a worst
case analysis, and the difference in distance is 482 km as a fraction of 38,380 km ...
482 / 38380 = 1.3% (rounded up)
... whereas for a satellite out at 28.2E, we would have ...
smaller number than 482 / greater number than 38,380
... which must be a smaller percentage than the above, which anyway was rounded up, so the difference in distance just cannot be greater than
around 1.2%. See also the discussion about the elliptical shape of the coverage pattern below.
Now think of the dish sizes for Zones 1 & 2, here's a dish available as either Zone 1 or Zone 2... https://www.amazon.co.uk/Satellites-Zone-Satellite-Dish-FreeSat-2-NO-QUAD/dp/B077DQTPYX/ref=sr_1_16
... which is ...
Zone 1: 60 x 40 cm
Zone 2: 80 x 60 cm.
The boresight cross-sectional area for each of these dishes is Pi.a.b
where a and b are the semi-major and semi-minor axes respectively. So
we have ...
Zone 1 Cross-sectional Area: 1,885 cm2
Zone 2 Cross-sectional Area: 3,769 cm2
... so a doubling of cross-sectional area.
I don't see how a 1% increase in distance can explain a doubling of dish area!
2. Beam centre will probably be aimed at southern England, so in Scotland you will be off the narrow beam with a weaker signal. (works the other way too, you CAN pick up UK channels in Spain, but you need a BIG dish).No again, look at the coverage map in the link given by Mark Carver.
The area of strongest signal includes the entire UK except Shetland, the entirety of the island of Ireland, and Normandy. Shetland is in the
fringe zone, as probably is Iceland though this is not shown on the
coverage map (I think someone said recently here that you could get
British satellite TV in Iceland).
The coverage pattern is roughly elliptical, which is exactly what you'd expect from a conical beam, circular in cross-section, irradiating the curved surface of the earth at a slanted angle. Again as expected, the semi-major diameter lies along the line from 28.E, going roughly from
Thanet through Liverpool and the Isle Of Man and onwards between
Scotland and Northern Ireland. This means that, say, Aberdeen is about
the same distance from it as St Ives or Lands End in Cornwall, they are
each about 260 miles or 420 km straight line distance from Liverpool,
and therefore, based on distance from the centre of coverage alone,
these two places should require about the same size of dish. But, see
also below.
Note: There is a cutout in the Atlantic, but, in the absence of
evidence to the contrary, I assume that this is entirely fictional,
caused merely by lack of data because no-one lives in the Atlantic, and
that actually the coverage pattern is actually near-elliptical. It's
not truly elliptical because as the earth's surface curves away from the satellite into the North Atlantic, the coverage is spread over a wider
area and, despite the cutout, this spreading is noticeable in the
coverage map.
3. More atmospheric attenuation - more signal lost passing through more atmosphere.Yes, my first reaction before making my OP was to guess that this might
be a major cause of the need for a bigger dish, and many replies since
have also mentioned this. Now, having understood the near-elliptical
nature of the coverage pattern as above, we can do some calculations for
the two locations previously established to be equidistant NE and SW
from its semi-major diameter. Putting these two places into a sat
calculator reveals that, although there is about 437 km difference in distance to the sat (so, as predicted, less than that given in the first calculation for a satellite due south, and divided by a greater distance
= smaller percentage change), the main difference is the elevation
settings required, 19.8 and 24.3 degrees, so, in the absence of other
more convincing suggestions, greater attenuation of the signal
travelling a greater distance through the atmosphere does indeed seem to
be the cause of the need for a bigger dish.
Aberdeen (57.13,-2.10) https://satlex.de/en/azel_calc-params.html?satlo=28.2&location=57.13%2C-2.10&la=57.13&lo=-2.10&country_code=uk
Azimuth angle: 145.17° (True North)
Elevation angle: 19.83°
...
Distance to satellite: 39578.52 km
St Ives, Cornwall (50.20861,-5.4875) https://satlex.de/en/azel_calc-params.html?satlo=28.2&user_satlo_dir=E&la=50.20861&lo=-5.4875&country_code=uk
Azimuth angle: 139.06° (True North)
Elevation angle: 24.31°
...
Distance to satellite: 39141.72 km
--
Fake news kills!
I may be contacted via the contact address given on my website: www.macfh.co.uk
On Saturday, 7 May 2022 at 00:16:03 UTC+1, Java Jive wrote:
SNIP
There are several real reasons: -
1. Further away, although not that much.
No, sorry, but this just cannot be the explanation. Consider ...
The calculation still quoted above for a satellite due south is a worst
case analysis, and the difference in distance is 482 km as a fraction of
38,380 km ...
482 / 38380 = 1.3% (rounded up)
... whereas for a satellite out at 28.2E, we would have ...
smaller number than 482 / greater number than 38,380
... which must be a smaller percentage than the above, which anyway was
rounded up, so the difference in distance just cannot be greater than
around 1.2%. See also the discussion about the elliptical shape of the
coverage pattern below.
Now think of the dish sizes for Zones 1 & 2, here's a dish available as
either Zone 1 or Zone 2...
https://www.amazon.co.uk/Satellites-Zone-Satellite-Dish-FreeSat-2-NO-QUAD/dp/B077DQTPYX/ref=sr_1_16
... which is ...
Zone 1: 60 x 40 cm
Zone 2: 80 x 60 cm.
The boresight cross-sectional area for each of these dishes is Pi.a.b
where a and b are the semi-major and semi-minor axes respectively. So
we have ...
Zone 1 Cross-sectional Area: 1,885 cm2
Zone 2 Cross-sectional Area: 3,769 cm2
... so a doubling of cross-sectional area.
I don't see how a 1% increase in distance can explain a doubling of dish
area!
"not that much" about 2.5% based on your figures.
3. More atmospheric attenuation - more signal lost passing through more atmosphere.
Yes, my first reaction before making my OP was to guess that this might
be a major cause of the need for a bigger dish, and many replies since
have also mentioned this. Now, having understood the near-elliptical
nature of the coverage pattern as above, we can do some calculations for
the two locations previously established to be equidistant NE and SW
from its semi-major diameter.
Putting these two places into a sat
calculator reveals that, although there is about 437 km difference in
distance to the sat (so, as predicted, less than that given in the first
calculation for a satellite due south, and divided by a greater distance
= smaller percentage change), the main difference is the elevation
settings required, 19.8 and 24.3 degrees, so, in the absence of other
more convincing suggestions, greater attenuation of the signal
travelling a greater distance through the atmosphere does indeed seem to
be the cause of the need for a bigger dish.
Indeed maybe I should have put it first. About 2.5 times as much atmosphere by rough calculation, depending on latitude
--
Fake news kills!
I may be contacted via the contact address given on my website:
www.macfh.co.uk
On 07/05/2022 10:05, R. Mark Clayton wrote:
On Saturday, 7 May 2022 at 00:16:03 UTC+1, Java Jive wrote:
SNIP
It's actually 1.1%.
Now think of the dish sizes for Zones 1 & 2, here's a dish available as
either Zone 1 or Zone 2...
https://www.amazon.co.uk/Satellites-Zone-Satellite-Dish-FreeSat-2-NO-QUAD/dp/B077DQTPYX/ref=sr_1_16
... which is ...
Zone 1: 60 x 40 cm
Zone 2: 80 x 60 cm.
The boresight cross-sectional area for each of these dishes is Pi.a.b
where a and b are the semi-major and semi-minor axes respectively. So
we have ...
Zone 1 Cross-sectional Area: 1,885 cm2
Zone 2 Cross-sectional Area: 3,769 cm2
... so a doubling of cross-sectional area.
I don't see how a 1% increase in distance can explain a doubling of dish >> area!
"not that much" about 2.5% based on your figures.No, the difference in distance is only 1.1%, and even were it 2.5%, it
still wouldn't explain a doubling in dish cross-sectional area.
And because the signal falls off with the square of the distance the difference is 21%.
On Saturday, 7 May 2022 at 12:49:50 UTC+1, Java Jive wrote:
It's actually 1.1%.
Just worked it out properly and it is 10%.
And because the signal falls off with the square of the distance the difference is 21%.
Originally $ky used 19.2 E, which is about the same longitude as Warsaw, but since it went digital it is on 28.2E, which is the about the same longitude at central Ukraine.
On 07/05/2022 21:06, R. Mark Clayton wrote:
On Saturday, 7 May 2022 at 12:49:50 UTC+1, Java Jive wrote:
It's actually 1.1%.
Just worked it out properly and it is 10%.
Nonsense:
Aberdeen (57.13,-2.10) https://satlex.de/en/azel_calc-params.html?satlo=28.2&location=57.13%2C-2.10&la=57.13&lo=-2.10&country_code=uk
Distance to satellite: 39578.52 km
St Ives, Cornwall (50.20861,-5.4875) https://satlex.de/en/azel_calc-params.html?satlo=28.2&user_satlo_dir=E&la=50.20861&lo=-5.4875&country_code=uk
Distance to satellite: 39141.72 km
The percentage difference in distance is thus:
100 * (39578.52 - 39141.72) / 39141.72 = 1.1%
St.Ives is on the South Coast at 50 degrees N as in the original
example, Aberdeen at 57 degrees N is significantly further north than
the border at 55 degrees N, yet the difference between their distances
to the satellite is only 1.1%, so the difference between somewhere 50
degrees N and somewhere else 55 degrees N cannot be more than that.
And because the signal falls off with the square of the distance the difference is 21%.Again nonsense ...
Ignoring the effects of atmospheric absorption, Aberdeen's signal
intensity will be proportional to
1/39578.52^2
... which we can write as being equal to ...
K/39578.52^2
... where we don't know what the value K is, but it doesn't matter, and
St Ives' signal intensity will be proportional to ...
1/39141.72^2
... which similarly we can write as
K/39141.72^2
The percentage difference between them is thus
100 * (K/39578.52^2 - K/39141.72^2) / K/39141.72^2
The Ks cancel out, and multiplying top and bottom by 39141.72^2 gives us:
100 * ( 39141.72^2/39578.52^2 - 1 )
= 100 * ( 0.978 - 1 )
= -2.2%
--
Fake news kills!
I may be contacted via the contact address given on my website: www.macfh.co.uk
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