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Transmitters and their Quirks

December 20, 2009

We spent the week working with Harris on the HTHD+. More precisely we have been working with them on the FlexStar exciter. Apparently we have some sort of PLL anomaly, or at least that is what we are investigating now.

We have limited connectivity to our transmitter site, so we use a single T1 circuit that carries our main audio and our HD data. This bottleneck seems to cause a clocking issue and when it gets too far out of whack (for lack of a better descriptor) the PLL goes nuts and mutes RF on the exciter. With more information from our frequency monitoring service we discovered that the transmitter was drifting in frequency, too.

We shipped our exciter back for evaluation and have installed a loaner. We went to air on it Friday, and so far we have been on the air since. I will be checking the PLL logs we are collecting to see how this exciter deals with our bottleneck of a data network.

I cannot blame any manufacturer here. I do feel that iBiquity could have/should have done a bit more testing of their algorithms and encoding so such issues could be avoided. There are many stations with limited bandwidth to their transmitter sites. If we were not forced to jump on this HD bandwagon so soon, maybe this situation would never have happened.

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