RTE Announce FTA Saorsat service

However an old Sky box will never work.
A "Sky HD" box in theory can work, but likely never will as Sky would need to change the software. There is disincentive for Sky to do that.

The OMT is very heavy (likely filters in it). It's not needed at all when there is no TX/BUC and if you have a single port dual polarity LNA (or even single polarity for Ka-Sat TV). The LNB is about 2x normal wieght as it has separate H and V waveguides/Ports.

Anyway... Current configuration without the BUC is 938g, nearly 1kg. I think with sensible horn and no OMT (none is needed even for dual polarity) and single port LNB (single or dual polarity) the weight could be 400g or less.

The horn is far more elliptical than sky dish horn.


The Hughes LNB has two rectangular ports (separate H & V) and the depolariser/re-polariser thing has obviously a square wave guide (H & V) at one end and round at horn end. For matching you maybe need a minimum amount of circular waveguide between horn and polariser.

that is the beghining
http://www.lyngsat.com/9east.html

mar1us wrote: »

that is the beghining
http://www.lyngsat.com/9east.html

See post# 1148, page 77.

Healy1 wrote: »

so is it possible to buy lnb yet?

No, and probably won't be for a few months. You can be sure that as soon as they become available, someone here will post about it.

A setup which I definitely wouldn't copy as it's on an ESB pole.

Stinicker wrote: »

There appears to be another pole right behind it so I reckon this guy just used a second hand ESB pole specifically for mounting his two dishes to rather than mounting them on a live active pole.

Or the other pole could be a telegraph pole.

Seeing as how yiz are all so interested in the shaggin' pole, I asked him

LoTwan wrote: »

I put the pole up myself. It was the original ESB pole that was decommissioned when the subterranean supply went in. We recycled it from it's previous position to it's new home on the boundary. We didn't take off the ESB notice purely because I didn't get around to it ;-)

Can we now get back to dishes?

Apogee wrote: »

yiz are all so interested in the
shaggin pole

Careful now this is a family forum

The transponder has been switched off for at least a week as far as I can see, and was still off yesterday when I checked.

They mustn't have appreciated the free publicity

Not a dicky bird in terms of Saorsat. There is a data/beacon TP (which I can't lock) so you should be able to check that your aligned OKish on 9E either with a bog standard signal strength meter, or a spectrum analyzer if you have access.

It's the fat peak at 1374MHz IF or 20124MHz.

No, it's not that tight!

Either it's not running, or you are not aligned or some other problem.

Don't forget alignment is nearly four times more sensitive. Your 110cm dish on Ka looks almost like a 2.2m for Ku.

2 different variations on the footprint - still no EIRPs.





from here:
http://www.vatm.de/fileadmin/pdf/vortraege/2011/satellite-day-2011_tooway.pdf

The NE Scotland used to be marked same as Cornwall / Wales.

The edge of NI. is 1/3rd of distance between the two spots, so it's hard to say. But it does make it unlikely that any of mainland UK will get Saorsat.

Each spot is 238MHz bandwidth and only two bands used. The remaining two colours achieved by LH or RH circular polarisation

LH + higher = Blue
RH + higher =
LH + lower =
RH + lower

lower transponder freq approx 19.7 to 19.940 GHz band

higher transponder freq approx 19.96 to 20.2 GHz band

(based on LNB band and need to have as large a guard band between transponder frequencies).

You can also see which spot corresponds to which Gateway - GW3 is Elfordstown.

http://finder.tooway-instal.com/fixe/pages/index.html

Spot beams from http://www.satbeams.com/satellites?norad=37258

Ka-Sat spot-beam 17


Ka-Sat spot-beam 20


Ka-Sat spot-beam 14

The Cush wrote: »

So when they refer to 20118 as a centre frequency, what is it the centre frequency of and how wide is that frequency (237 MHz?)?

It's the one in the photo - it shows up as 1374MHz IF or 20124MHz (the analyzer is uncalibrated and a few MHz out).

Based on the Tooway manual, I reckon Belfast should be fine. Those Satbeam maps look quite a bit off to me - too far south.

The Cush wrote: »

So when they refer to 20118 as a centre frequency, what is it the centre frequency of and how wide is that frequency (237 MHz?)?

How many transponders would be required for 4 frequencies and 2 polarizations (i.e. 4 spot beams, excluding the other 78) - 1, 2, 4? Is it possible to split a transponder in a number of virtual transponders i.e. different frequencies and/or polarizations?

It's the centre frequency of the 1st data carrier, DVB-2 / DOCSIS downlink.
It's roughly 50MHz wide (Related to symbol rate).

Each spot (there are about 82) uses an entire single transponder. So 82 x 238MHz transponders.. At least one Ku Satellite has 64 transponders.

So EVERYTHING on the Irish spot (2 x RTE carriers and 3 x Internet carriers, only one listed for now) is on a single transponder dedicated to the Irish Spot. There may also be narrow band beacons for control and telemetry.

The bandwidth possible for a transponder is bit more than 10% of the frequency. So even without advances in technology a ka Transponder will have twice the bandwidth of a ku transponder. Often nowadays what is called a "Transponder" on a satellite is simply a DVB-S or DVB-S2 multiplexed carrier.

The bandwidth needed for a carrier is approximately the symbol rate for DVB-C, DVB-C2, DVB-S and DVB-S2.

So RTE 25Msym/s is about 25MHz, about 1/8th to 1/9th of a transponder. Eventually they will need a second carrier for content on 2nd DTT Mux.

The raw Bit rate is approximately symbol rate x bits per symbol
bits per symbol is 2 for QPSK (as there are 4 possible patterns 2^2 = 4).
bits per symbol is 5 for 32 APSK (as there are 32 possible patterns 2 ^ 5 = 32).
The FEC setting is roughly amount of data after Error correction.

so 1/2 means corrected data rate = 0.5 x Raw rate.

(all approximate).

The Internet connection modulation mode vary with weather unlike TV broadcast, so the data rate varies. This means in heavy rain you don't lose connection (maybe QPSK), and in Clear sky (maybe 32APSK) you get more speed.

So the frequencies in the table are carriers about 50MHz wide. Since RTE will eventually use 2 x 25MHz (approximately) that leaves 3 x 50MHz (approximately) for Internet DVB-S2 downlink. Depending on Weather and dish size that's
50 x 2 x 0.5 approx in heavy rain = 50Mbps
50 x 5 x 8/9 approx in clear sky = 222Mbps

They claim 70Gbps for satellite. That's 850Mbps per spot
if you can put 4 x carriers each 50M symbols / sec (the upper limit of a modem or DVB-S2 receiver anyway, most DVB-S modems/TV receivers are 45M sym/s max), then in very very heavy rain your total capacity is 200Mbps. According to the 70Gbps, they assume 850MBps/4 = 212.5Mbps

It's likely the 70GBps is sum of uplink and downlink, so expected average speed closer to 110Mbps per carrier per spot.

They are only going to add 2nd, 3rd and 4th carriers as carriers "fill up".

At 50:1 contention and 10Mbps user, you have 550 users per carrier. At more typical satellite contention of 500:1 you have 5,000 users per carrier, or 20,000 users per spot.

Saorsat essentially removes 1/4 of the Ka-Sat capacity for internet on Irish Spot. But in east Coast and Border areas (and further with bigger dish) they can add Irish users to Welsh and N.I. spots if Irish capacity is exhausted.

The low download cap per hour, day, week as well as month is to allow up to 500:1 contention to work. In other words, even on Ka-Sat, Internet access will be rubbish compared with 10Mbps on UPC, Fixed Wireless, Fibre or DSL if they sell more than 10% of their target.

My theory on the four dishes on Ka-Sat is:
1) The feed horns end diameter (minimum spacing) vs F/D for dish vs spot diameter set a minimum spot spacing (maybe about 4 degrees)
2) Each dish can be slightly offset by half the angle of spots of same "colour", (maybe about 2 degrees) to fill in the gaps between spots and ensure overlapping coverage
3) Each dish has 1/4 of the 82 feeds needed for system. With 25 "notional" horn offsets that's a 5 x 5 grid. (More than 5 LNBs in a row on a regular receiving dish gets poor). Some dishes have 20 and some a few more giving total of 82 rather than 100. The Viasat1 (launch this year or next?) is same design as Ka-Sat and has more spots.

Hmm...

It's possible I suppose that the high and low 238MHz "bands" share a transponder. Sounds a bit wideband. 500MHz on one 19.7 to 20.2 GHz transponder (25% bandwidth)? I suppose not impossible. It would explain size of gap as filtering between TWT (or other device) and feeds needs a gap between bands.


That would make Ka-Sat 41 transponders = 82 Spots and Viasat 1 56 Transponders = 112 spots?

I don't know. 41 and 56 sound more reasonable numbers. Spots with SAME frequency even if opposite polarisations absolutely can't share a Transponder.

In either case, there is only one physical transponder used for an entire spot. If the transponders can run the entire 19.7 to 20.2 GHz band, then each transponder is used for two spots, one is higher part of band and one is lower part of band.

I'm not calling it low and high band as there is also a "low" ka band 19.2Ghz to 19.7Ghz and a higher Ka Band 20.2 to 20.7GHz

Well, the 70Gbps and 140Gbps are both a bit hypothetical peak capacities. More so in areas with rain.

watty wrote: »

That would make Ka-Sat 41 transponders = 82 Spots and Viasat 1 56 Transponders = 112 spots?

62 spots only covering the high density areas of N America according to http://www.satbeams.com/satellites?id=2462