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Sean Mota

SatelliteGuys Master
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Supporting Founder
Sep 8, 2003
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I have invited Rod Hewitt who is the author of TSReader at Cool Stuff to chat with us regarding Satellite, MPEG, Motorola compression algorithm and some terminology used by Motorola in the VOOM receiver.

I really like to keep all commentaries out of this post and stay with a Question format. You may enter a comment follow by a question but ALWAYS end your comment with a question.

I think it is also time for us to go to the system settings menu and ask any terminology used in the Motorola box to be clear on it.

One question I have for Rod is about Rain Fade. Why? I have a Dishnetwork system and others have DirecTv 18" Dishes. A lot of us have experienced rain fade with Voom. Some had requested a larger dish and this seems to make a difference; There are three terms in the system setting menus of the VOOM box.

1-Signal Quality
2-Signal Strength
3-SNR (Signal Noise Ratio)

(a) What is the relation between the three?
(b) why the Fain Rade on VOOM (even for customers in the East)?
 
Thanks for doing this Q & A, Rod. What kind of impact does the Voom STB box have on OTA reception? Does the box have built in methods of dealing with multipath that are inferior or superior to other satellite STBs? Thank you.
 
Some people have reported better PQ using the component (analog) output than DVI. A possible explanation is the HDTV itself, but can you think of any other possible reason on the STB-side?
 
True manuals...

Where can we find a REAL manual for the STB? There are a lot of things in the settings area(s) I'd like to know about.

The Rickster
 
vurbano said:
why didnt voom start with mpeg4 and wm9? why even mess with mpeg2?

First, let me mention MPEG-4. It is very unlikely this will ever be used for traditional "to the TV" broadcasting. It's just not bitrate efficient enough. The real candidates for the next generation DBS system are WM9 (aka VC-9) and MPEG-4.10 (aka AVC aka H.264).

The Motorola broadband group has plenty of experience doing MPEG-2 satellite systems - a large proportion of cable and satellite channels are delivered using the Motorola big dish system, i.e. Digicipher II. They don't have any announced experience with the next generation codecs.

Currently the only shipping manufacturer of WM9 encoders is Tandberg and I'm sure Motorola wouldn't want a big client like Voom using encoders from anyone other than Motorola! Additionally, there's no decoder hardware that's reasonably priced yet for either WM9 nor MPEG-4.10.

I imagine that Motorola has a lot of breathing room to work on their next generation implementation now that Voom has annouced they'll use capacity on AMC6.

Rod
 
cyuhnke said:
Thanks for doing this Q & A, Rod. What kind of impact does the Voom STB box have on OTA reception? Does the box have built in methods of dealing with multipath that are inferior or superior to other satellite STBs? Thank you.

I don't have a Voom receiver so I really can't say. If you open yours up and are able to look inside the 8VSB tuner module you might be able to figure out which demodulator chip is being used. Knowing which demod is being used will tell you the generation of 8VSB receiver - the third generation demods like the ATI NXT-2004 do significantly better when subjected to multipath.

I doubt if it's a Motorola designed 8VSB recevier.

Rod
 
Rod said:
First, let me mention MPEG-4. It is very unlikely this will ever be used for traditional "to the TV" broadcasting. It's just not bitrate efficient enough. The real candidates for the next generation DBS system are WM9 (aka VC-9) and MPEG-4.10 (aka AVC aka H.264).

I imagine that Motorola has a lot of breathing room to work on their next generation implementation now that Voom has annouced they'll use capacity on AMC6.

Rod
Whoaaaaaa this isnt my understanding. You mean we are not getting wm9 or mpeg4.1 this year applied to SD and to HD next year? Because the PQ of this current codec according to many users is less than the PQ of Dish and directv.
 
Rod,

Is the DVI output span PC or TV? Does it run from 16 as black or 0? What about white 255 or less?
 
So I guess this was a 5 minute Q & a session? Thanks for your help Rod. The information you provided, although limited, was very useful. Hopefully you'll be able to come back.
 
Hello Rod:

How about answers to Sean's questions in the first post of this thread? (Signal Quality, Signal Power, SNR)

Thanks.
 
>> Additionally, there's no decoder hardware that's reasonably priced yet for either WM9 nor MPEG-4.10.<<

Wow, this pretty much contradicts what Voom has stated about going wm9 this year. If they are still in developmental phase, there's no way they'll be able to deploy it this oct or dec.

Or HAS Voom stated that, or it's just us inferring something we shouldn't?

edit: wm9 is starting to sound like vaporware. Worse, if wm9 is delayed, what will this do to the dvr? Won't it be too costly for them to have a dvr with no wm9 that will have to be upgraded to wm9 later on?
 
Sean Mota said:
One question I have for Rod is about Rain Fade. Why? I have a Dishnetwork system and others have DirecTv 18" Dishes. A lot of us have experienced rain fade with Voom. Some had requested a larger dish and this seems to make a difference; There are three terms in the system setting menus of the VOOM box.

1-Signal Quality
2-Signal Strength
3-SNR (Signal Noise Ratio)

(a) What is the relation between the three?
(b) why the Fain Rade on VOOM (even for customers in the East)?

Sorry for the delay in answering this. I had a new release of TSReader to get finished first.

Signal Quality and Signal Strength are not really standardized. Most likely the Signal Quality is a combination of the strength and the SNR.

Signal strength is most likely related to the gain being applied to the AGC (automatic gain control) inside the tuner. The stronger the AGC is driven, the weaker the signal so you can think of the signal's waveform strength in terms of inverted AGC gain.

SNR is simple - signal to noise ratio. The trick here is if the SNR is before or after the error correction.

I'd be interested in knowing what typical values shown are for these three variables (I don't have a Voom receiver).

On to the rain fade. First, the ONLY thing you can do about rain fade is to try to get around it with gain, i.e. a bigger dish. That said, even with a big reflector if there's enough antenuation in the atmosphere, you're going to loose the signal. For example, I have a 1.8 metre dish pointed at AMC-1 in the Ku-band and it even looses signal during heavy downpours.

So, why would Voom be worse than DIRECTV or Dish Network?

Looking at their signal on a spectrum analyzer, they're a bit weaker than Dish's signals at 61.5w - perhaps 2-3dB down which is surprising. Maybe Voom is keeping the power down because their TWTAs (the amplifiers on the satellite) aren't linear enough which is a big factor when dealing with 8PSK signals. But then the 8PSK signals transmitted by Voom have a better error correction algorithm than the DIRECTV/Dish QPSK transmissions so this most likely isn't an issue.

Most likely there are three reasons:

1. Anyone west of the Mississippi will be looking through a lot more atmosphere than for the more centrally located DBS orbital slots.

2. Timing is bad. I have dishes pointed at 119, 110, 91 and 61.5 with receivers on those locations running on a single channel full-time. When it's stormy here I can see the direction of the storm by looking at which channels are out. With most storms moving west to east, I see 119, then 110, then 91 and finally 61.5 go out one by one as the storm passes by. Quite often when the storm is almost over, I'll see video back on 119/110 but still out at 61.5.

3. The skew angle on the dish is wrong. This is quite complex so bear with me.

This is easier to think of in terms of linear (vertical/horizontal) versus circular transmissions. Imagine a satellite at 100 degrees west and you're at 100 degrees west. If you point a dish at this satellite and want a vertical signal, the feedhorn will be perfectly vertical because there's no skew in the signal.

Next you pack up your bags and move to 90 degrees west. Now there's a 10 degree skew in that vertical signal so to optimize the signal you adjust the feedhorn by 10 degrees. However you need to think about what that vertical signal looks like - it's no longer bouncing off the relector straight down the middle - it's now at a 10 degree offset hence the feed needs to be lined up.

But the big issue here is dish illumination since we're dealing with a circular polarity transmission. So, you're at 100 degrees west and trying to receive 61.5 west. The signal coming from the satellite is skewed by almost 40 degrees and because of that angle the dish won't be illuminated as strongly as it should. You have to rotate the entire dish by 40 degrees to get it fully illuminated.

This is why multi-satellite feeds like the 3rd generation DIRECTV and Dish Network DishPro dishes all have a skew adjustment - to keep the dish on the same angle as the satellite arc and therefore illuminate the dish better.

I would very much imagine that Voom's 2nd generation antenna (for 61.5 and AMC-6) will have a skew adjustment.

HTH,
Rod
 
Thanks for the info, Rod!

Better late than never. Helped me understand a bit more about satellite reception.

Still watching HDTV even through Seattle clouds, Gill
 
Rod said:
I'd be interested in knowing what typical values shown are for these three variables (I don't have a Voom receiver).

Rod

Can someone post these values? Rod, these values seem to change from channel to channel. Here in NYC, the strongest values I get on HDnew (channel 100) but it changes to lower values in a channel like Starz-HD. I was not home last night so if someone can post a few numbers of Satellite Signal Quality, Satellite Signal Strength and NRS plus the channel you took the information from. If you can go to another channel (like Starz) also post the information.
 

signal needed for ota?

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