Monthly Archives: September 2013
This was a video test to confirm new (H.264 /MPG4) encoders from WELLAV we’ve been testing in-house in combination with DVBS2 modulation techniques to prove increased payload on smaller space segment bandwidth. Finally received the Azimuth model AZ110 Encoder from Newtec. Since being introduced to Newtec at SMPTE meeting last year, I’ve been reading up on the improvements of DVBS2 modulation over the old DVBS which should yield a +18% increase efficiency and payload due to their FLEX ACM methods. The following is an actual test of live video utilizing these key components;
- WELLAV – Model SMP100 H.264 Video encoder to 20MB.
- WELLAV – Model UMH 160R “IRD” (Integrated Receiver Demodulator)
- NewTec Azimuth – Model AZ110 DVBS2 Modulator to L-Band Output
- Tandberg 5600 DVBS old modulator w a Newtec If – L-band converter
- Test source: Canon HD Camcorder with HDSDI output
- Audio source, SONY Blue Ray player – DVD Eagles “Hell Freeze Over”
- Agilent Spectrum Analyzer – In line with L-band receive downlink feed
- Pixel to Pixel 18.5” color monitor by ViewZ with built in Waveform Vector scope Audio Meter
- TrustComm Teleport Supplied: 1.8Meter Prodelin fixed dish with Paradise 25W BUC feed on L-band at 1235 MHZ.
- MODCOD’s – QPSK at ¾ FEC, DVBS2 (AZ110 Final)
- Satellite: AMC-15 at 105W.
Special thanks to EchoStar folks in Denver and Trustcomm Trusted Networks and in particular my partner in crime today, Tim Knowles station RF engineer. I have to toot the horn of these folks I have worked with for the past 4 years who were and continue to be very accommodating. Thanks to Tim Dubose – Director Solutions Engineering who ran all the initial link budgets and pre-engineering for me for this configuration and assigned Tim to me. Also to Ron and Kelly in the front office and of course Scott Winebrenner who pulls together all the resources around the Earth Station and my long time NOC Manager friend Pete Licce. Without these people, I could never pull this off. Big FAVNET THANKS!
Should be noted that original link budgets were calculated on APSK at FEC 4/5 and I elected to change the modulation rate to QPSK and FEC of ¾.
I have to say it’s really nice to have Tim Knowles at the controls leading me through the set up and getting up on the bird so easy. Tim put up a CW (Clean Wave) and peaked and poled out the antennae prior to my arrival, which saved time. We started out by configuring the L-band output back to back with the Input to the IRD (WELLAV UMJ 160R) to verify L-band transmit and receive frequencies and establish proper video encode rates and ASI stream to decode in the IRD. Source signal is CANON HD camera with HDSDI output set at full 60fps HD 16:9 and terminated to input of encoder (WELLAV SMP100).
We began the test using the older Tandberg 5600 and Newtec L-band conversion modulator. Initially we had bad and torn pictures with a bad repeating vertical screen that would lock up in full picture. So after an hour of hit and miss attempts to no avail, we switched to the new NewTec AZ110 to see if it was an Encoder or Modulator issue. Much to our delight it came up straight away! Ah ha! So with some quick calculations we realized what the ASI output stream should look like and I adjust the SMP100 Encoder down to match the Symbol Rate/Mbaud rate of the modulator in the AZ110. It should be noted that when we first slammed the encoder into the NewTec, it was set too high (factory default) of 34MBpbs, which blew away the Tandberg and created a FIFO alarm “RED” font panel indicator. This was all done in less than 5 minutes, and just before our lunch break, I suggested we take our newly balanced load and switch back to the older Tandberg, and Valla it works! Now to be completely fair to Tandberg who has made great transmission equipment for decades, this is looking at two different decades of technology, not to mention the age of the gear itself. We noticed a lot of automatic settings in the Newtec for modulation gain compensation. Obviously these folks have put considerable time into smoothing out the bumps in the road for satellite transmissions and it shows with novice new operators. Oh yeah, did we say, the unit didn’t have an owner’s manual, so we were stumbling through set up menus, which after one gets used to everything being access through left right arrow keys in a “horizontal” fashion as opposed to the old school vertical scrolling found on Tandberg, we were good to go! Also we found the CW (Clean Wave) or “Pure Carrier” (NewTec’s Description) function, which made lining up with the NOC at Echo star a breeze when we signed on and verified our pole/cross pole and power levels. Very easy and quick!
|Video Mod Test||Mod. Rate||FEC||MODCOD||dB Level||Symbol Rate||SMP100 Video Encode Rate MBPs||SMP100 Audio KHz||SMP100 ASI MBPS||Comments|
|Tandberg 5600||6MHz||3/4||QPSK||-22.3||5,000||4,500||64||7,260||Choppy, requires 4 decimal symbol to ASI rate|
|NewTec AZ110||6MHz||3/4||QPSK||-22.5||6,000||5,980||128||8,500||Locked up quick, looks good, more video payload|
|Newtec Test 2||9MHz||3/4||QPSK||-22.5||9,500||9,500 -10,500||128||10,000||Looked better, smoother, faster motion|
|Newtec Test 3||12MHZ||3/4||QPSK||-22.5||13,760||12,500||128||11,600||Best look, biggest payload Mbps video|
Now for the fun stuff! Yep, fire up the engines, let’s make and transmit video 28,000 miles into space, I said.
No picture? Turns out that the WELLAV 160R Receiver wants the actual frequency not a converted offset L-band reference, it makes up and converts internally, which is a really nice feature. Simply plug in 12869 MHZ and it figures out the rest! Once again, Valla, and now were seeing live video and my Eagles singing along. Much better than wind noise off the shot gun mic on the camera. Also I have found a trick over the years about H.264 mpg encoding video, listen to the audio and it will tell you when you are clipping the video or over-modulating. Drop outs in video are noticeable in audio as audio gets squashed out first. This is analogous to the old IP saying, “big trucks run small cars off the road.” These audible cues should be early warning signals for transmission errors about to cascade into really noticeable ones in the picture as well. Yes, if things are in balance, you should have enough room for nice smooth 128Kbps audio along with your 8 bit video. Whether fiber transmission or over satellite, this audio trick always holds up.
So we now have a nice clean carrier up. We’re feeding it 7260Mbps of ASI made up of 6500MBps video + 128Kbps stereo audio. Things couldn’t be smoother. But I want to know if I can push the encode levels up to 7Mbps video, which I did but started to clip out the audio. Ok, found the upper limit. Our output on the front panel shows -22dbM relative power. With all the complex signal chain to the BUC it’s not easy to get a true sense of power, even with the Agilent Spectrum Analyzer looking at the return downlink feed in line with the IRD. So, Tim Knowles said, let’s pull the BUC in, put it on the bench, put a dummy load on it and fire it up with the same level and we can get an accurate level, which we did. Much too our surprise we utilizing only 12-14 Watts from the 25W BUC. We can only get within 1-2 dB of accuracy here due to the test gig and its calculations. Still not bad as I’m thinking that with sticking to only 6MHZ and not going up to 9 or 12 MHZ I can get away with lower power, mostly due to the more efficient modulation of the DVBS2 Flex ACM which the NewTec provided us. In contrast we need closer to 18-22Watts to accomplish same level on older DVBS modulation standard.
So then we pushed the carrier up to 9 MHz opened up the ASI to 13,100Kbps or 13.1Mbps and pushed the encoder up to 10,500 Video encode rate (CBR). I should note that I kept the H.264 in CBR as I wanted to see best/worst case scenario on modulation and I was not trying to cheat any additional bandwidth out of content or lack of motion in the JPG fields. Yes, this look really nice too, maybe a little smoother on the motion side, so we did some fast pans and pulled pretty hard left to right to create motion. No motion artifacts that were visible to my naked eye.
We eventual opened up to 12MHZ carrier increasing to 15MBps on Video encode rate just fine.
Now for one final note, that is definitely worth mentioning. We decided we had seen all the modulation with adequate power levels on the return feed we’re viewing, but what about “Rain Fade” and low power conditions?
So, we went back to our standard 6MHZ set up and started lowering the power on the AZ110 down.
We lowered output to -34.9dB before the IRD lost its “LOCK” light LED and stopped decoding video. The Agilent was now flat lined and we didn’t see how we could possibly still be on the air. So we bench tested and calculated that it was around 1dBW in power when we finally crapped out! Geez what a great receiver this UMH160 has, very forgiving. We all know we can turn the power up, but having greater receive sensitivity means we had a link budget delta somewhere around 12-14dB. That’s a lot of rain fade for those math challenged. Could mean the difference between keeping program on air and just fading out to black or worse, NOISE.
So, it’s not just the modulation, power and transmit chain, it’s also the TRVO station equipment and in particular the receiver that has to be credited as well. So my conclusions;
6MHz with 6.5MBPS payload, looks great is my “Best Value’ solution, for contribution content for DSNG for sure, with regional sports or secondary market program feeds. Most economical use of MPG4 video over satellite. Wouldn’t hesitate to use this 80% of the time
9MHZ – with 10,500MBps video payload, for Sports & Entertainment needing more depth of field, higher motion content that is more demanding national feeds. Nice happy medium between having more depth and not blowing out your space segment budgets on long shows.
12MHZ – Best quality with tons of headroom, if you’re not worried about space segment bandwidth costs. 20MBps video encode rates can be expected here, but we did not push it that high. My notes say we were at 15MBps video.
18 MHz – Who needs this! This is the final point here for my old analogue transmission satellite users.
I still hear producers saying, oh I need 18 MHz on this show etc.! Why I ask?! Have you actually seen a difference?
With mezzanine level H.264 encoding and soon to be H.265 married up to the DVBS2 modulation and added FLEX ACM by Newtec, there is absolutely no reason to burn up that much bandwidth to get the same or better results. Now, one could argue that you could put two or even three streams into an 18MHZ carrier and that makes good sense to me. Why not have multiple feeds or camera shots? Or even a pre-groomed IPTV content feeds readied for mobile apps? BTW – Most CDN’s now generate on the order of 8 feeds of varying content encoding for delivery now.
Now, we didn’t utilize my favorite Tektronix VM700 video analyzer, but I feel for motion content testing, one is best to use your eyes and pay very close attention.
As always, these are my subjective opinions and you are welcome to yours and can disagree with mine.
Until next time!
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