One of my favorite Android apps is glSDR, which connects to any of several remotely hosted software defined radios. Those dspervers, as they are called, enable me to listen to HF signals in Europe and North America. On my smartphone, from ratty little coffee shops with internet access (or my ratty little apartment), I can tune the ham bands, HF aero frequencies, and even Brother Stair - with ease. The experience is like having a commercial / laboratory grade radio in my pocket. No joke, these exceed the capabilities of the Rockwell or Rohde & Shwarz on the aircraft I fly. These last 4 weeks have been good because more people have started hosting dspservers. Also, existing hosts have improved their equipment. KF7O was on for many days testing a miniature "Hermes lite" SDR, and it sounded great. N8DMP has reduced the impact of strong broadcast stations on his Cleveland area dspserver. N6AS, in California, appeared for a few days feeding his dspserver with the very fine ANAN-100 radio. I have been quite impressed at the quality of these radios - especially the ones running Hermes boards. Noise floors tend to be low, below -100 dBm. I am a stickler for signal purity, and am happy to see this good practice of using minimal amplification and low noise hardware. Intermod hasn't been an issue on any of the radios. Not only are the signals coming in clean, but without exception they are dead-on frequency, stable, and without any artifacts or hum on the audio. I can enjoy very nice auto notching for interfering carriers, effective noise blanking for pulse noise, and flexible bandpass filtering. Some of the dspservers are connected to softrock hardware. I am less impressed with the softrocks, but they still work pretty well. These receivers are smaller, use less energy, and use a different downconversion method than the Hermes radios. Typically, the noise floor is in the -50 dBm to -70 dBm range. Frequency accuracy is not hair-splittingly on, due to a different clock reference in use. Usually the offset is less than 100 hz, and not a big problem to fix by bumping the frequency digits up or down as necessary. The European dspservers are quite good for monitoring HF broadcasts from the Middle East and Asia. Interestingly, there's plenty of activity late at night on the 20 meter band in Europe. They get the Americas during the first half, then Australia / New Zealand / Japan in their pre-dawn hours.
