iBiquity Digital has released an interim report on its early findings in actual field tests of an SFN digital FM IBOC booster located in the greater Baltimore area.
The field tests involve two stations operating under FCC experimental station authorizations. WD2XAB operates from Columbia, MD, (iBiquity's home town) on 93.5MHz with 1.5kW ERP analog, 150W ERP digital, 456' HAAT and serves as the main IBOC digital hybrid station, while W2XAB-FM1, the SFN booster station operates with 50W ERP digital at 446' HAAT from a site located roughly 20 miles northeast of WD2XB.
The scope of the test thus far has been to operate the digital-only booster in both synchronous and time-aligned modes with the main signal. Digital reception test runs are then made in coverage areas between the two points using a van equipped with an HD Radio receiver and spectrum analyzer.
Preliminary results indicate that operating the booster with time alignment provided significantly improved digital reception in listening areas where the two signals overlap, as opposed to synchronous-only operation. This suggests that problems with digital signal degradation in areas where significant main/booster overlap occur can be managed using time-alignment techniques.
The current iBiquity report does not include characterization of digital-to-analog interference generated in the vicinity of the booster site. IBiquity notes that these results will be forthcoming, although a review of the tests published in NAB's Tech Check indicates that additional tests taking place in Boston at Greater Media's WKLB will include the addition of a synchronized analog component to the booster signal to mitigate expected near-field digital to analog interference.
All of the above tests are being financed with the assistance of the NAB's Fastroad technology initiative.