How to get your IBOC measurement groove on is coming to the NAB Radio Show.
The first of two IBOC panels is slated for 10 a.m. to noon on Thursday, Sept. 18. The session is called “HD Radio Measurements Workshop.” As moderator David Maxson, managing partner of Broadcast Signal Lab, stated to me recently, the RF masks for IBOC are Power Spectral Density Masks; PSD is measured in power per unit frequency — dBm/kHz.
It is important to get the PSD correct for two reasons: 1) To minimize potential interference in the broadcast bands, and 2) to maximize the quality and reliability of the hybrid IBOC signal.
“Measuring digital signals is more complicated than measuring analog signals,” said Maxson. “Digital signals have a noise-like quality that challenges the measuring instrumentation and the person measuring. There have been situations where two measurements done by two different people result in opposite conclusions about whether a certain signal passes or fails the mask.”
The NRSC IBOC Standards Development Working Group has been developing a set of guidelines for measuring hybrid IBOC signals so there will be one way to do it against which all other methods can be compared.
“The measurement session will show how to make a proper Power Spectral Density measurement against the mask,” Maxson said.
Only at this session:
Special things David is planning for the workshop include a “CHIMP” demonstration; that’s a Combined Hybrid IBOC Measurement Package for measuring those IBOC signals that segregate the FM analog and digital signals on separate transmission lines. He credits Randy Mullinax of Clear Channel Radio with creating CHIMP and says engineers can build their own CHIMP from basic parts.
Also at this session, Maxson plans a demo of measuring a hybrid FM IBOC signal as well as a demo of taking measurements of an AM transmitter “live” in the room. The planned demo includes skills such as how to align the magnitude and phase components of an AM IBOC transmitter before proceeding to measure the Power Spectral Density of the signal.
An illustration of the effects that mistuned AM arrays have on the hybrid signal is planned as well, with presentation assistance by Grady Moates of Loud and Clean Broadcast Science.
The workshop will be rounded out with a discussion of the limitations of directional couplers in sampling digital signals.