Saorsat Coverage

There is not currently (December 2010) ANY satellite in service that could deliver Irish Domestic Television without Encryption. The UK mainland is a market TWENTY times bigger than the Irish one. Even "home produced" content would be much more expensive if it could be received in Mainland UK other than by using large mast and big aerial pointed at Ireland on parts of Welsh coast and Cornish coast. 

[Update: Ka-Sat entered service commercially for Internet Applications 31st May 2011. RTE Tests have been received since 26th May 2011]

The solution for RTE NL is to use a Satellite designed for Internet coverage that is was launched 26th/27th December 2010. It should be available for use around end of May 2011 if everything works.

There has been some confusion about the Ka-Spot size.

Early indication of centres of each spot

alt_kasat

Later version

ka-sat-spot-beam-coverage

The above map is NOT normal footprints, but  service areas

The large spots are SAME footprints as the small spots. This article tries to explain why the small ones are about 1/4 area of the "real" footprint.

There are only four colours needed to arbitrarily colour or fill any map. So it's not a coincidence that the Ka-Sat has four dishes each with about 20 offset feeds. A rectangular waveguide to a feed horn to illuminate the dish is most efficiently Horizontal or Vertical polarised. For Ka-Sat, the H or V is converted to/from Left Hand or Right Hand circular polarisation just between horn and feed. The Circular polarisation is an advantage on Ka Band in the rain and allows better separation of the polarisations. Also to separate Transmit and receive you need band pass filters. Again the simplest arrangement is two transmit and receive bands. Two bands and two polarities gives the four "colours". Each spotbeam is associated with a 237 MHz wide transponder, so each carrier is in fact a carrier, and not a transponder.

Not Ka-Sat Plan. Just illustration of similar scheme

    hb6-ka-freq

Possibly HB6 Ka-Band frequency plan (hashed areas are on-board multiplexing)

(Note: Ka-Sat plan is NOT the same)

ka-sat-spot-beams-reuse

Colours showing Frequency/Polarisation (LH or RH circular) re-use. Service areas, not true footprints

(now obsoleted)

Ireland and Calais France are "Lime/ unripe lemon" colour. 

See top left pyramid of "smarties"

Scotland = Blue  Ulster, West Scotland = Dark orange
Ireland = Lime/Lemon  England = Pale Orange
South West England = Blue  France (Calais) = Lime/Lemon

See Spain? Centre of Spain is Blue, then around that, pale Orange, Olive/Lemon, Dark Orange, Olive/Lemon, Dark Orange, Olive/Lemon.

The  isolated spots on edges of overall coverage  can be used with larger dish to quadruple the service area because they are isolated.

The four combinations in the graphic above. The next graphic a possible assignment, showing area with the same band and polarity as the same colour. Since all the spots/beams are from the same Satellite, it's impossible to receive Spot Nx  if you move too close to Spot Ny, where N are two matching spots and x and y are two locations.

Irish-Scot-v3

The solid patches  are official main service areas.

(Update June 2012: Edge of solid spot is transition from 80cm to 110cm. Dark contour is likely about 110cm and limit)

The first magenta ring indicate contour of what a published service area might include with a still "normal" size dish (80cm to 110cm)  The outer magenta ring is low signal needing very large dish (1.2m to 2.5m) as it overlaps same settings of French Calais spot and East Scotland spot.  It must be low enough to cause no interference. The spots come from the SAME satellite, so along a line at tangent (purple line)  to the two lime circles gets equal signal from both feeds (spots) no matter how big the dish is. Because it's the same satellite. In fact of the four dishes on the satellite, it's two separate offset feeds on the same dish. You can only separate the signals enough, reliably, by moving within the Irish or French Blue circles (with Lime fill) along the line between their centres. If the symbol rates, power and drop off of signal from France is enough that Co.Down coast to  Ballycastle in Co. Antrim gets only just low enough interference to work on Irish Spot, then the red line marks the edge of possible Irish reception, but only if the French Spot has a similar carrier. As the symbol rate is lowered and frequency shifted, then the Red and Purple lines move toward the French spot.  Conclusion is that if there is no interfering French signal a large dish might work as far as UK Midlands. If there is a French Calais signal overlapping the Saorsat carriers, then no matter what size dish, the coverage is limited to the Welsh coast.  See satbeams

(Thanks to Apogee, The Cush and John1000 on boards.ie for various links)

Initial Data Downlink spots

Number Beam
color
Symbol
Rate
Centre
frequency
Polarization
1 Blue 50 19.73125 RHCP
2 Orange 50 19.99375 RHCP
3 Purple 50 20.11875 LHCP
4 Green 50 19.85625 LHCP
RTE Purple 25 20.18500 LHCP

So the "blue" rings or coloured spots on the Ka-Sat maps don't represent footprints, but service areas. A foot print (signal coverage) has contours of signal strength.

astra_2D_north-sml

 

Typical Ku Spot Beam Footprint (Astra 2D)

The top left edge to North West is clipped as beyond that point the signal drops very rapidly to zero as the receive dish Elevation is too low as Satellite falls to horizon on view. The 10 degrees Elevation is regarded as a minimum. The Centre 50cm area is about twice as big as a Ka Band spot as the "narrowness" of a beam varies with frequency for  same size dish and is about half moving from Ku Band to Ka Band. The contour lines are lines of equal signal. You can see that dish size rises quickly as you move away from Britain and Ireland. Some people further away are using 3.6m dishes  (360cm).

The Dish Contours for the current live service should be about  90, 150 200, not 44, 70 and 110

ka-irish-foot-sml

Irish Footprint if no Interference from French Spot.

Note that dish sizes are based on early prelaunch info and DO NOT APPLY to Saorsat

(44cm = Really 90cm,70cm really 150 and 110 really 2m)

ka-sat-irish-int-sm

Irish Footprint with Dish for London and French Footprint
London might get French Signal or just Interference

Dish size used or needed does not affect the degree of Interference
Between French and Irish Signals versus location.

The approach of using a bigger dish with Ka-Sat won't work. It will work with Ka satellites that don't have frequency reuse. Without the Frequency/polarisation reuse the Irish Spot for Ka would cover about 1/2 diameter, or 1/4 area of the Ku footprint above. It would be received in London with a bigger dish.

Irish-Scot-v3

So no matter HOW big the dish is the dark purple contour just outside the solid footprint is likely close to the limit of coverage.
Probably 110cm for decent rain margin and 60cm in perfectly clear sky.

How does Ka-Sat have 80+ spots yet only four Dishes?

The 80+ spots are from about 20 feeds each on four dishes. A total of 80+ offset feeds.

feedcluster-ka-sat

Partially assembled feed unit. Ka-Sat has four of these, each with 20+ feeds.

One for each of the four dishes on the Satellite

(You can see the rectangular waveguides, each Offset feed horn thus has only one polarisation)

art-kasat
Artistic impression of Ka-Sat in Orbit showing  the four Dishes.

(Artist's concept courtesy of Eutelsat)

(Probably one for each polarity (LH or RH circular)  and band)

The solar panels are thought to be 20m long, each!

It's hard to see exactly where the four sets of offset feeds are mounted.

The exact real number of offset feeds, and "real" transponders is unknown. Modern satellites tend to have "virtual" transponders where the published transponders are really just separate carriers (virtual transponders) sharing a physical set of receivers and transmitters (a Transponder). On board Multiplexing means various received signals can be switched to different transmitters rather than the older "monolithic" transponder which was an LNA practically connected direct to a TWT. Current information (May 2011) is that there are 82 Ku Transponders each 238MHz bandwidth. That's about 12% of the frequency, so sounds plausible. The spot layout suggests each feed cluster creates spots offset by about 4 degrees, with alternate clusters interleaved to a 2 degree offset.

What does this tell us?

Because the French spot and the irish spot highlighted in olive are from the same Satellite, the proportion of signal from each at any location is the combination of location and beam width. On a line at tangent to the two orange rings touching, the signal is equal. So this means that if the same Polarisation (LH or RH circular), frequency, symbol rate and FEC is used, the signals can't be separated at all along that North East / South West angled line. No matter how big the dish is,

In Cornwall, Anglesea and Wales you are still within the purple contour, the edge of which is probably low enough signal to not interfere with signal within Blue area. even when Irish spot is at lower power (very clear sky) and French spot at maximum power (heavy rain) the desired signal (Irish Spot) is severely degraded by French Spot, if it has signal in same part of band. A bigger dish equally increases both signals. The ratio of desired to unwanted (Eb(Irish)/Eb(French) ) stays the same.

The actual design power level is not published, but depends on FEC, symbol rate, Modulation and the Dish size on the Space Craft (Satellite). It does not depend at all on the receive dish size at all as all spots are from the same satellite. The receive dish size never affects the Eb/I (Signal vs interference) between spots, only the Eb/(No+I) (Signal vs Noise & Interference) from non Ka-Sat sources (Cosmic/Sun/Earth Noise and other satellites' Interference).

Conclusion

The dish size on the satellite sets the minimum spacing of the Offset feeds for a reasonable size service area. If an offset feed at the edge of the feed cluster on the Satellite is further offset, then the usable area spot can be larger. We see this on the map above, thus the usable area of the Irish spot for an "normal" size dish could be four times area, almost 1000km (approx 600mi) diameter rather than the "usual" approximately 500km (300mi) diameter. But if there is a spot of the same band & polarity, then service is limited to the smaller area. This why the Irish Spot may be able to be received in the Western Isles but not in most of Mainland UK.    

    

kasat-overall

Combined Service Areas of Ka-Sat for Internet Coverage.

This is not a signal footprint!

Built for Eutelsat by Astrium using the Eurostar E3000 platform, KA-SAT ushers in a new generation of multi-spotbeam satellites. Its revolutionary concept is based on a payload with 82 narrow spotbeams connected to 10 ground stations. This configuration enables frequencies[/polarisation] to be reused 20 times and takes total throughput beyond 70 Gbps. The ground network will use ViaSat’s SurfBeam® technology, similar to the solution already powering broadband connectivity for almost 450,000 satellite homes in North America. The combination of KA-SAT’s exceptional capacity and ViaSat’s SurfBeam® technology will make it possible to deliver Internet connectivity for more than one million homes, at speeds comparable to ADSL.

KA-SAT will in particular boost to up to 10 Mbps the speeds of Eutelsat’s Tooway™ consumer broadband service, which has been operated since 2008 by its Skylogic affiliate. Tooway™ satellite antennas equipped with dual feeds will be able to benefit from broadband connectivity via KA-SAT and broadcast services delivered by satellites located up to 10 degrees from Ka-SAT’s 9° East location. By driving down terminal and transmissions costs, KA-SAT will also lower the barrier to entry for VSAT services for connecting enterprises, providing back-up for private networks, facilitating emergency communications and for transport markets. With each spotbeam delivering total capacity of 900 Mbps, shared between the forward and return paths, significant new resources will also be opened for services needing high throughput and quality that include regional television, newsgathering and connecting local networks to the Internet backbone.

The deployment of the KA-SAT programme, both in space and on the ground, will be pursued with three key phases prior to full entry into commercial service. The first phase comprises circularising the satellite’s orbit, with four firings of the apogee motor over the coming seven days. Once the satellite is on station at 9° East, it will undergo a series of in-orbit tests. This will be followed by the final phase of integrated validation of the satellite and ground stations before commercial entry into service, which is planned for end May 2011.

Via Eutelsat