> What exactly is the purpose of the sweeping/frequency changing oscillator?
It's part of a Hewlett-Packard network analyzer. There's a lab-grade directional coupler used, so the load can be measured for both resistance and reactance. There is a Smith chart screen display. It shows the curve for the frequencies being swept. Each current transmitter has a requirement for the load as measured at the final amplifier transistor collectors. This varies from model to model. That load will vary according to the power combiner that sums the individual transistors in that amp. This optimal load gives the cleanest bandwidth for the audio, and - sadly in this case - for IBOC signals. There are adjustments made to the antenna phasing and matching system to optimize this. Sometimes it requires additional components. There is something called antenna pattern bandwidth for every directional system. In some cases, the pattern shape varies significantly from -10KHz to +10KHz. If it's too far off, then IBOC doesn't work. The upper and lower digital carriers get too far off in power from each other and break the HD reception. That's why they do the sweep, to measure the load and then include the calculated pattern bandwidth to the final analysis of the system to determine HD compatibility. There are some stations where the pattern bandwidth is out of the limit requirements. WDDZ-550 looks to be in that boat. The only fix for that is to increase the tower height to a 447' 90 degree tower from the 300' 60 degrees ones in use now. Might be tough, as there's an airport not too far away. Expensive, too. Craig Healy Providence, RI _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
