Gary O’Guinn, Assistant Chief Engineer, KTUU-TV /
04.24.2014 12:00 PM
Rohde ETL Helps Keep KTUU-TV Signals Clean

Rohde & Schwarz’s ETL TV Analyzer

ANCHORAGE, ALASKA—KTUU-TV, the NBC affiliate for the Anchorage market, has a six-decade history, and serves viewers residing in an area of more than 586,000 square miles (about the size of California, Texas and Montana combined). As part of our DTV transition, we started evaluating test equipment that would allow us to do real-time monitoring and measurement of the entire transmission chain, including encoder, microwave STL and transmitter. In addition to being able to perform the necessary measurement tasks, we also gave a lot of consideration to the portability of the test equipment.

UNEXPECTED CONSEQUENCES
Interestingly, during a demonstration of one candidate system—Rohde & Schwarz’s ETL TV analyzer—we discovered that our PCR jitter was out of specification. As part of our evaluation process, we looked at other stations in our market and soon discovered that every one of them had similar PCR jitter issues. As it turned out, all of the stations were using the same encoder and a recent firmware update had turned off the genlock signal, allowing the systems to run free and create PCR jitter.

Needless to say, the R&S ETL had proven its usefulness with this revelation and it was an easy choice to purchase one for our use.

Since then, the ETL has proven its utility time and again. We use the system on a regular basis to evaluate our off-air performance and it’s the “go-to” tool when we discover a problem in the RF or MPEG domain.

LOCATING WHERE ‘THE PACKET STOPS’
Another example of the instrument’s usefulness in tracking down problems is an issue we experienced after shifting from microwave to fiber as our primary means of delivering studio signals to the transmitter. We’d been using a 13 GHz microwave STL, however, the signal path was over a large body of water which sometimes made propagation unpredictable and occasionally resulted in dropped packets.

To eliminate this, we decided to move from microwave radio to fiber for our primary studio to transmitter link and relegate the microwave system to backup status. We enlisted the services of two local telecommunication companies to establish the fiber path for us.

Nevertheless, we again experienced dropped packets, but this time there were no environmental conditions to blame.

Using the ETL, we began to isolate the problem by monitoring our signal off-air and using the instrument’s MPEG analysis function to identify and log dropped packets. (This was occurring on a fairly regular interval—about every 10 minutes.)

Applying the same methodology to both our transport stream handoff to telco “A” and their subsequent handoff of our signal to telco “B,” we were able to quickly trace the problem to the switch used to go from “A” to “B,” and negotiated the necessary corrections with the service provider.

The R&S ETL TV Analyzer is a powerhouse of functionality and its combination of DTV analysis, MPEG transport stream analysis, and portability make it a key tool used by our engineering team to ensure that KTUU-TV is on-air with the picture quality that our viewers have come to expect.

Gary O’Guinn is assistant chief engineer at KTUU-TV and has been with the station since 1974. He may be contacted at garyo@ktuu.com.

For additional information, contact Rohde & Schwarz USA at 888-837-8772 or visit www.rohde-schwarz.com.



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