Technical Topics, April 2000
The NASWA Short-wave Simulator
Short-wave listeners have recently discovered the many radio stations, available free for the listening, via the Internet. With RealAudio’s Real Player 7.0, and Windows Media Player software, streaming audio has never sounded better. Stations from all over the world are just a mouse click away. Some stations are even in stereo. CBC Radio Two from Toronto streams a beautiful stereo signal as do WQXR in New York and KING-FM in Seattle. All four BBC domestic radio services are now available 24 hours a day.
As more and more of us get cable TV modems or DSL service via our telephone lines, we can all listen 24 hours a day to any station of our choice. And we can listen at higher data rates than previously possible on ordinary dial-up modems. What a wonderful time to be alive.
But every sunny day has a dark cloud lurking just below the horizon. Something is wrong. While I was at the SWL Winterfest last year I became aware of an ominous trend among NASWA’s program listeners. Can the sound actually be too good?
Many short-wave listeners have complained that audio via the web does not have the same thrill we have when listening via our radios. All stations are heard with approximately the same quality regardless of distance. There are no static crashes, jammers, co-channel interference, or selective fading effects induced by ionospheric multipath propagation. You don’t get the feel that the station is broadcasting from the other side of the planet.
As a service to NASWA’s program listeners, the NASWA Research Laboratory has once again come to the aid of the listening community. If you remember, a few months back, I described a software-implemented short-wave simulator that was developed to expedite testing of various digital transmission modes for Digital Radio Mondiale. The program mathematically injected various forma of simulated degradation into the data stream so engineers trying to hammer out a universal digital transmission standard could assess the robustness of various approaches. Now, with the cooperation of Digital Radio Mondiale and Thomcast, the NASWA Research Laboratory has acquired rights to incorporate this software in a new device designed to restore the thrill of short-wave listening to the antiseptic sounds of Internet radio.
A block diagram of the system is shown in Figure 1. The audio output is sampled at the speaker output of your audio card. The audio passes through the NASWA Short-wave Simulator where various operator selectable degradations are mixed with the audio. At the output of the box the audio feeds a tiny three-inch diameter speaker designed to provide the distorted, tinny sound we all love from our cheap transistor portables. There is also a serial RS-232 interface to your computer which enables you to select the desired combination of interference sources via an on-screen mixer board.
![[ block diagram of the NASWA Short-wave Simulator ]](/journal/images/tech_generator.gif)
Figure 1: Functional block diagram of SW simulator. The modular design facilitates listening to Internet audio sources and makes them sound just like they were coming from your short-wave receiver.
As an extra cost option, there is a software plug-in module for Windows 95/98 that automatically downloads the latest A and K index observation data from Boulder. The data is transferred to the simulator via the RS-232 serial interface where it is used to set the severity of fading and flutter. The user must input data on receiver and transmitter latitude and longitude so the box can make appropriate choices depending on how close the simulated path comes to the polar auroral zones. At present there is no provision to simulate long delay echoes, or trans-equatorial E layer propagation. If market surveys show members want this feature, the NASWA Research Lab will consider it for a later version release.
Because there are new sources of interference coming along all the time, the NASWA researchers decided to incorporate the patterns on flash memory modules. This means your simulator box will never be obsolete. When new sources of interference appear, just check into the NASWA web site and download the new update free. The NASWA software will automatically install the new data in the appropriate function generator module via the RS-232 serial interface.
Not to be outdone by Amazon.com, the NASWA Company Store is also jumping into the on-line sales business. If you go to this URL: <http://www.naswa.net/nrl/> you can see how to purchase the short-wave simulator with your credit card. Pennsylvania residents will automatically have sales tax added so be sure to provide an out-of-state shipping address so we won’t know you live in Pennsylvania.
Be sure to visit the web page above to get price information and detailed specifications. Until next time, stay tuned.