RTE Announce FTA Saorsat service

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.

watty wrote: »

I updated this recently and today
http://www.techtir.ie/saortv/saorsat-coverage

I know this is slightly off topic but this is something that has been bugging me as a fan of FTA TV: is the days of the widebeam astra and other satillites coming to an end and we will be limited to narrow localised content on tight/narrow beam satillites?

Thanks to all of ye for compliling all this info about this in the thread - it has been and is an interesting read

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

The Cush wrote: »

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

Hmm less spots and more capacity. Maybe the 110 figure I'm thinking of is current WildBlue which is two Ka band satellites.

62 spots and 56 transponders suggests some transponders using two sub bands of frequencies and thus feeding two spots. You would only need 6 dual frequency transponders shared. 50 spots + 12 spots.
If all the transponders are the same on Viasat1, then 50 spots would have twice the capacity of remaining 12. In USA they found with WildBlue that some spots fully subscribed (edges of cities may have big populations and poor or no cable access) and fully rural spots under-subscribed.

So this re-enforces the 2nd thoughts that each Ka-Sat transponder serves 1 or 2 spots (some may serve only one spot) via using 2 x 238MHz per transponder.

No doubt eventually more information will dribble out. For sure with 82 spots any particular spot can ONLY be one or part of one transponder, so if there are 2 x RTE frequencies and 3 x Viasat/Tooway/Eutelsat Internet "Services" each 50Msym/s those will be 5 carriers on a single transponder.

An "official" document does refer to ka-sat having 238MHz Transponders. But if that is only 41 transponders, it's maybe too little for 70Gbps+ capacity. If each transponder has only 238MHz and there are 41 rather than 82, then the high part and low part of band would be only 119MHz each. That would mean the Irish spot would be "full" with 2 x 25Msym/s RTE Saorview and 1 x 50Msym/s Internet (DOCSIS DVB-S2 downlink).

In such a case you can only have 20,000 customers on a spot with no TV, if contention is 1000:1! Or 1000 customers at 50:1. In Ireland then due to Saorsat there would be 1/2 this = 10,000 customers 1000:1, 5,000 @ 500:1 and only 500 customers @ 50:1 contention.

You can see why they may be coy about exact configuration of Transponders as they don't want people to see how rubbish the congestion could be with the claimed capacity of Internet customers. (Hylas1 is worse as the spots on it cover a much larger area).

watty wrote: »

I think that may be a recent map as they originally talked about 10 to 12 gateways and there are now only 8. Elfordstown appears to serve 10 spots.

Yes, you're right, I didn't notice all the other spots attributed to GW3.

I wonder what's the rationale behind the way the spots are distributed among the Gateways? I was expecting each Gateway to service a specific region in Europe (e.g. Elfordstown to cover Britain and Ireland), or for each Gateway to be linked to a set band/polarisation (e.g. Elfordstown serving green spots).

I found this presentation which some small additional techinical specs.
http://www.gvf.org/docs/oil-gaz-europe-11/D1_1400_Nicholas_Daly.pdf

warlikedave wrote: »

I know this is slightly off topic but this is something that has been bugging me as a fan of FTA TV: is the days of the widebeam astra and other satillites coming to an end and we will be limited to narrow localised content on tight/narrow beam satillites?

Thanks to all of ye for compliling all this info about this in the thread - it has been and is an interesting read

No one has an insight or opinion into this? just thought id ask.

hi - still can't seem to get a lock on any signal - what are the exact transponder and setting you are using on your receiver apogee so i can try them on mine/

No intention to be "sharp". It HAS been discussed at length already on this thread. New threads are free. There is a thread on Astra 1N already mentioning this too. You'll get more response and discussion on a separate thread.

thanks -

all ive done is park the dish on 9e - take the ku off and put my homemade holder for the ka lnb on - then blind scanned with a spiderbox and a az hd box no joy - then i've treied 11996 no joy either - i can't enter the transpoder strting with a 2 like your v+ can - i think i'll need the meter out tomorrow - to check - just hope the loop is still there again!

i'd like to know issa's settings - he seems to have then on an different transponder to you - his box probabley reads them like a spiderbox - but hi picture as just a bit hazy .

i'll try that - isaa's picture looks like transponder 11966 -

nah still nothing - out with the meter tomorrow .

thanks for the az hd box settings - had a play about wiht these setting but i can only get a maximum of 70% signal with no quality.


i'll try again tomorrow!