DRM SDR Monitor Receiver/Spectrum Analyzer

HCJB engineer John Stanley has long tried to develop awareness of DRM within the amateur radio community, and he says that a great deal of progress has been made in that regard. He said that the Amateur Radio Handbook now contains quite a bit of content on DRM. There have also been many articles about DRM in QST magazine and another magazine for radio experimenters.

The latest work that Stanley has been involved with is developing a DRM software-defined receiver and spectrum analyzer. He explained that "this is a very inexpensive way of observing some of the signals you need to observe in order to maintain a DRM transmitter."

The three most important pieces of test equipment that a transmitter engineer has, or wants to have, according to Stanley, are an oscilloscope, a network analyzer and a spectrum analyzer - many of which are very expensive items. But there\'s good news, says Stanley. "One of the tendencies of the past few years is the development of test equipment that allows you to use the power of a laptop - or a desktop - to enhance your ability to observe signals. By adding a relatively inexpensive front end, we can come up with a pretty powerful piece of equipment."

John Stanley has developed a small digital oscilloscope which is a lot easier to take through airport security than a normal large-size oscilloscope. He recommends the use of a $660 Ten-Tec network analyzer which can replace a $20,000 HP unit. And he has developed a simple spectrum analyzer using a mixer, an oscillator and the sound card of a laptop which can again replace a $20,000 or $30,000 piece of test equipment. His software-defined radio starts with analog filters and then converts them to digital.

"When you start transmitting in DRM," said Stanley, your engineers will ask you for expensive spectrum analyzers so they can guarantee that the transmissions are legal. But with a few hundred dollars\' worth of equipment and a good laptop, you can do the same type of measurements." Stanley says you can get the software for this analyzer free from various sources. He particularly recommends WINRAD, for example, which is completely free. This low-cost analyzer is a simple way to check if your transmitter is on frequency and to check the audio bandwidth.

Stanley offered files and CD\'s to anyone interested in pursuing these projects, and he provided some sample recorded audio files simulating real-time monitoring to demonstrate what his equipment can do. For more details, see the PowerPoint labeled "DRM SDR Monitoring Receiver Analyzer" which will appear shortly on the NASB website (www.shortwave.org) under Annual Meeting files.