DRM Diversity Receiver

John Wineman works at HCJB\'s Global Technology Center. He spoke to the DRM USA Group annual meeting about improving broadcast coverage with DRM.

Wineman explained that missionary organizations often have small networks of FM stations which need to be fed with programming from a central location. He said that in some countries, missionaries carry program tapes on motorcycles to the station locations, but among the other disadvantages of this, it doesn\'t allow for live programming. FM relays can be placed approximately every 30 miles, but this is expensive and there are licensing complications. Phone lines can be used, but quality can be poor. Internet feeds can be used in some locations, but they are not practical in many others. Satellite distribution provides good audio quality, but a satellite transponder often costs $4000 per month, which makes it prohibitive.

But one other alternative is DRM. Wineman said that near vertical tropical band shortwave can be used to cover distances of about 100 miles, using different frequencies at different times of day. DRM on these frequencies provides excellent audio quality, but the need for switching frequencies creates gaps in coverage at the time of morning and evening frequency changes.

HCJB is working with LeTourneau University in Texas to develop a diversity DRM receiver. Wineman said it\'s just a matter of time before DRM receivers become available on the commercial market, but it will be a longer time before a diversity DRM receiver comes along. The theory behind this type of receiver is that the programming will be sent to two HF transmitters (because of the need for a crossover period at the time of frequency changes in the morning and evening). The same programming will be broadcast on both transmitters to a network of diversity receivers at each of the FM transmitter locations.

An industry sponsor, Rockwell Collins, is working with the team at LeTourneau. Rockwell has 12 experts working with HCJB, university faculty and senior engineering students to develop a software-defined DRM receiver. During the past year, Wineman says they have come up with good requirements definitions for the software receiver, developing specifications for each of the digital downconverter modules, etc. They have designed the hardware and have built prototypes of each submodule and tested them. The objectives for the next year are to finalize and publish the final documents, and to develop a plan for integrating the modules and testing.