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Thanks again everyone. I love learning about how this all works.

I am trying to understand what reverse band is going to do for us. I thought it was needed for 4K bandwidth but I guess not if they have it working on KA. I am guessing one 4k channel takes up a entire transponder. Woah. Is the reverse band going to give more capacity in some way?

I understand a litttle tiny bit about what reverse band is but still a little confused.

Thanks again.

mysticseer said:

Thanks again everyone. I love learning about how this all works.

I am trying to understand what reverse band is going to do for us. I thought it was needed for 4K bandwidth but I guess not if they have it working on KA. I am guessing one 4k channel takes up a entire transponder. Woah. Is the reverse band going to give more capacity in some way?

I understand a litttle tiny bit about what reverse band is but still a little confused.

Thanks again.

Click to expand...

Well ... from what we have been able to gather and simplifying somewhat. The Reverse Band gives DIRECTV 36 new additional 36 MHz wide transponders (18 each at 99 and 103W).

DIRECTV transmits their UHD channels at an avg. data rate of about 30 mb/s.

Now because DIRECTV uses modulation parameters of a 30 Mbaud symbol rate, QPSK modulation, and an FEC of 2/3 for their 36 MHz wide nationwide (plus Alaska) Ka tps., and will for their RB ones as well. This results in an approx. maximum data through-put of 40 mb/s.

So sending only one 4K channel per tp. at present on the Ka band waste some 10 mb/s of capacity on each tp. Obviously quite inefficient.

Therefore on the RB DIRECTV plans to bond three transponders together which will allow four 4K programs to be multiplexed together for a total capacity of 48 UHD channels without wasting capacity.

Thats ...

3 tps. x 40 mb/s through-put per tp. = 120 mb/s combined through-put capacity.

120 mb/s ÷ 30 mb/s per 4K program = Four 4K programs multiplexed across three tps.

So with 36 tps ÷ 3 = 12 three tp. groups = 48 UHD channels total capacity for the combined 36 RB tps. transmitted efficiently using all available bandwidth.

Instead of only a 36 UHD channel capacity while wasting 10 mb/s per tp. on. the RB transmitting only one UHD channel per tp. as is currently being done on the Ka band.

HoTat2 said:

Well ... from what we have been able to gather and simplifying somewhat. The Reverse Band gives DIRECTV 36 new additional 36 MHz wide transponders (18 each at 99 and 103W).

DIRECTV transmits their UHD channels at an avg. data rate of about 30 mb/s.

Now because DIRECTV uses modulation parameters of a 30 Mbaud symbol rate, QPSK modulation, and an FEC of 2/3 for their 36 MHz wide nationwide (plus Alaska) Ka tps., and will for their RB ones as well. This results in an approx. maximum data through-put of 40 mb/s.

So sending only one 4K channel per tp. at present on the Ka band waste some 10 mb/s of capacity on each tp. Obviously quite inefficient.

Therefore on the RB DIRECTV plans to bond three transponders together which will allow four 4K programs to be multiplexed together for a total capacity of 48 UHD channels without wasting capacity.

Thats ...

3 tps. x 40 mb/s through-put per tp. = 120 mb/s combined through-put capacity.

120 mb/s ÷ 30 mb/s per 4K program = Four 4K programs multiplexed across three tps.

So with 36 tps ÷ 3 = 12 three tp. groups = 48 UHD channels total capacity for the combined 36 RB tps. transmitted efficiently using all available bandwidth.

Instead of only a 36 UHD channel capacity while wasting 10 mb/s per tp. on. the RB transmitting only one UHD channel per tp. as is currently being done on the Ka band.

Click to expand...

Where do you get this idea they will be bonding three transponders together? The only public statements Directv made about this, a couple years ago, indicated they would be bonding two reverse band transponders together and delivering three 4K channels from each bonded pair.

slice1900 said:

Where do you get this idea they will be bonding three transponders together? The only public statements Directv made about this, a couple years ago, indicated they would be bonding two reverse band transponders together and delivering three 4K channels from each bonded pair.

Click to expand...

Well, I use to believe the same thing about only 2 bonded channels on RB.

But IIRC, I don't recall DIRECTV ever specifically saying it would be two bonded transponders.

I remember the claim of 30 mb/s for a UHD channel. And a stated capacity of "50" UHD channel capacity which was assumed to be approximate for an actual number of 54 (or 36 ÷ 2 x 3 UHD chs. per tp. pair).

But there are several problems with this 2 bonded tp. view in that.

1) DIRECTV would have to raise the data through-put rate of a 36 MHz CONUS+ beam tp. from ~40 to 45 mb/s for a 3 UHD channel multiplex.

2) 2 bonded tps. means one tp. used for regular HD/SD reception is inefficiently wasted as sealed off and not recoverable during 4K reception.

3) How can we be sure the number 48 is not what is really approximate for the number 50 stated in the article instead of 54?

4) Stuart, carl6, inkahauts, and others on the original HS17 testing group claim 3 bonded tps.

HoTat2 is correct in how many transponders will be bonded together as that's how the compression system is built out at DirecTV. It's been verifed by a few employees who work at DirecTV who hang out here and have hinted at the details.

HoTat2 said:

Well ... from what we have been able to gather and simplifying somewhat. The Reverse Band gives DIRECTV 36 new additional 36 MHz wide transponders (18 each at 99 and 103W).

DIRECTV transmits their UHD channels at an avg. data rate of about 30 mb/s.

Now because DIRECTV uses modulation parameters of a 30 Mbaud symbol rate, QPSK modulation, and an FEC of 2/3 for their 36 MHz wide nationwide (plus Alaska) Ka tps., and will for their RB ones as well. This results in an approx. maximum data through-put of 40 mb/s.

So sending only one 4K channel per tp. at present on the Ka band waste some 10 mb/s of capacity on each tp. Obviously quite inefficient.

Therefore on the RB DIRECTV plans to bond three transponders together which will allow four 4K programs to be multiplexed together for a total capacity of 48 UHD channels without wasting capacity.

Thats ...

3 tps. x 40 mb/s through-put per tp. = 120 mb/s combined through-put capacity.

120 mb/s ÷ 30 mb/s per 4K program = Four 4K programs multiplexed across three tps.

So with 36 tps ÷ 3 = 12 three tp. groups = 48 UHD channels total capacity for the combined 36 RB tps. transmitted efficiently using all available bandwidth.

Instead of only a 36 UHD channel capacity while wasting 10 mb/s per tp. on. the RB transmitting only one UHD channel per tp. as is currently being done on the Ka band.

Click to expand...

That post makes me feel like Penny and you are Leonard. I'll have to read it a couple more times!!

HoTat2 said:

1) DIRECTV would have to raise the data through-put rate of a 36 MHz CONUS+ beam tp. from ~40 to 45 mb/s for a 3 UHD channel multiplex.

2) 2 bonded tps. means one tp. used for regular HD/SD reception is inefficiently wasted as sealed off and not recoverable during 4K reception.

Click to expand...

1) If they wanted 30 Mbps for each they'd have to raise the transponder throughput to 45 Mbps. That means using QPSK 3/4 instead of QPSK 2/3. That requires only 0.93 db of increased signal margin, so it would hardly affect its resistance to rain fade.

2) Yes, but it would depend on the way they're implementing bonding. They've cooked up their own solution for bonding that's apparently software based, since they are continuing to use DVB-S2 hardware which offers no native hardware support for bonding like DVB-S2X does. I've surmised before that maybe the 'wasted' transponder is a limitation of the way they're doing it, but wouldn't necessarily be a permanent limitation. If they use DVB-S2X tuners in the HS17 follow-on, I'm sure Broadcom and Maxlinear would provide Directv a way to use the hardware bonding in their non-standard way if they requested it, similar to how they support Directv's hacked version of DVB-S2 as well as DSS.

I can't find the quote at the moment, but I'm 100% sure Phil Goswitz specifically said Directv would be bonding two transponders together to carry three 4K channels at 30 Mbps each. Obviously plans can be changed, and maybe they have if K9SAT (and apparently others in the testing group) are correct about this. Has anyone been involved in any actual testing of bonding so this can be treated as a known fact, or were they just told this? I guess what I'm getting at is whether they were specifically told that three transponders would be broadcast in a bonding triplet, or just that the receivers used three transponders for bonding? The former is not the same as the latter, if the implementation works the way I previously outlined at dbstalk.

I just don't think using three transponders makes sense for a couple reasons. First, bonding three transponders to carry four 4K channels is less efficient. Granted, they only go from 54 to 48 4K channels of capacity, and the way 4K is going nowhere we may never have even close to 48 4K channels so it might not matter...

Second, and more importantly, needing three transponders (and therefore three SWM channels) per 4K channel really limits receiver hardware. What happens when there are actually real 4K channels to watch, and people have all 4K TVs in their house, so people will want to watch/record 4K on every TV? If you need three SWM channels per 4K channel, a RB LNB's 21 SWM channels can serve 7 such channels which fits perfectly with 7 tuners (assuming a follow on to the HS17 that has three 8 tuner chips instead of two, and outputs 7 4K streams) Then what the heck is up with the DSWM30 supporting only 15 tuners per output?? People using those couldn't grab enough tuners to watch 7 4K streams, are those living in MDUs just screwed? OK, I've always said I expect Directv to eventually permit more than one HS17 per account, but until they do we can't assume they ever will.

That said, it seems there's now more evidence for three transponders bonded than two, since that's just based on Goswitz's statement from a few years ago, so that's probably how it is going to be. It doesn't make sense to me, but then a lot of what Directv has done the last few years make no sense. Why does the reverse band LNB drop down to 13 SWM channels when "certain hardware" is connected, even though all SWM capable hardware handles the full frequency range required for 21? Why is the DSWM30 limited to 15 tuners per output even though the chips inside it support more - the same chip as used in the reverse band LNB - so it could easily support 21 per output (more than that, actually...) I have to assume there's some method to this madness, but so far none is evident. Watching their decisions is like reading the news from Washington, so many things just make you say "WTF?"