Repack

A case of PEBKAC (Problem Exists Between Keyboard and Chair)? Tell us about your war stories!
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NECRAT
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Repack

Post by NECRAT » Fri Aug 02, 2019 3:24 pm

So it finally came and went, fairly quietly. We repacked last night at 1:05am. (Ch 20 to Ch 33) I turned on our new GatesAir ULXTE-90 transmitter at 55.6kW of power into our interim site/combiner. Our main transmitter guy shut down our 1998 Harris Sigma transmitter, one of the very first installed in the US for ATSC. (We were amongst the first DTV stations on the air in the country). For some stations it was a scramble for the last second. One station didn't get their equipment rack installed (made by an outside vendor) until 12 hours before primetime. This station is using an IP Link to feed their signal to the transmitter with no redundancy. The IP link was tested once earlier in the week, not retested. However corporate installed a new piece of network gear, and you guessed it. The IP stream is complete trash. The station has been publishing apologies for the issues on their website. It looks like a weak signal (it's not), and reception issues. The new Dielectric antenna does phased dynamic polarity, and we're all going in at different V Pole percentages. The antenna is working amazingly well.

Now we work on our primary site, which is going to require a very delicate balance of some very heavy tower work and modification work.
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grich
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Re: Repack

Post by grich » Fri Aug 02, 2019 9:58 pm

Not having a backup STL option is...wow. We heard a horror story of a station that didn't have a backup encoder and spent (I think) 4 days off the air. We still have our original Flexicoder and a NetVX still around for doomsday duty, and two matching Selenios as our main and backup encoders.

What's the plan for the primary site TX? I'm sure you'll live longer getting rid of the Sigma and the occasional KABOOMs from the crowbar circuits. :lol:

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PID_Stop
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Re: Repack

Post by PID_Stop » Mon Aug 05, 2019 8:20 am

NECRAT wrote:
Fri Aug 02, 2019 3:24 pm
This station is using an IP Link to feed their signal to the transmitter with no redundancy. The IP link was tested once earlier in the week, not retested. However corporate installed a new piece of network gear, and you guessed it. The IP stream is complete trash. The station has been publishing apologies for the issues on their website. It looks like a weak signal (it's not), and reception issues.
We send IP streams between our hub and a number of spoke sites, and most of our links are quite reliable and perform nicely with only a reasonable amount of FEC, but one of our stations had exactly the same problem: constant dropouts, horrible breakup. We ended up tunneling the stream through a QVidium ARQ link -- it's basically a PC at each end running Linux, with software that passes the stream with buffering at each end, and protocol to allow the receiving end to request retransmission of dropped, misordered, or corrupt packets. The improvement has been dramatic, taking the feed from being unusable to being virtually flawless. This same protocol is in the process of being standardized as "RIST", and it wouldn't surprise me if it becomes pretty much standard for IP links: it takes advantage of the return path (which FEC does not); moreover, unlike FEC which adds a constant overhead to the stream, ARQ / RIST only increases bitrate above the nominal stream rate whenever it becomes necessary to re-send packets. A very nice piece of kit!

Jeff

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