The radio receiver is an Icom IC-R7000. It has a frequency range of 25 MHz to 2.0 GHz (=2000 MHz). It supports the following modulation modes: AM, wideband FM, narrow band FM, and SSB. SSB sideband selection is done by a rear-panel switch always set for upper sideband. The R7000 has 100 memory channels, multiple scanning modes, front-end attenuator, infrared remote control, and loads of other features. The radio is connected to the serial port of a PC (see below) via Icom's CI-V Level Converter. Serial port control is a bit limited. For example, scanning functions are not supported.
We have two R7000 receivers. The first one was in service from January 1997 to March 1998. It was moved aside and a slightly modified R7000 has taken its place. This second unit has be adapted for a future feature of the web site (frequency scanning). As of mid-May 1998, these receivers have experienced 110,000 frequency changes. When in use, the radio is operational 24 hours/day. We have never experienced a failure of either ICOM. These are very rugged radios!
New site:
Bethesda, Maryland
Old site (before 18 June 1999):
The antenna is a commercial discone (WB-1300) on a 25 foot mast. Location:
North Latitude 39.07.532'
West Longitude 077.28.496'
Here is a diagram of the system architecture that was published in the February 1998 issue of QST Magazine. Click here to read the article.
From the IC-R7000, radio control is via a serial link to a 233 Mhz Pentium PC running Red Hat Linux 4.0. Audio streaming is via a sheilded audio cable to a Sun SPARC 20 running Solaris 2.6 and a 200 Mhz Pentium running the RealAudio Encoder under Windows 95. The Linux computer runs the web server. Web server requests from HTML forms or via the Java applet launch CGI programs . The CGI programs are written in Perl 5. They accept requests for frequency/mode changes, provide feedback as HTML to the requesting browser, keep logging files, and issue unix shell commands to the Linux and Solaris computers. The shell commands to the Linux computer run "icom", a nifty control program by David Mills at the University of Delaware. The icom program recognizes many Icom radios and allows unix hosts to control them via the serial interface. The shell commands to the Solaris computer start up a program called sfmike. The sfmike program is part of the Speak Freely. suite of unix programs for sending and receiving GSM 6.1 audio. The 200 Mhz Pentium encodes the live audio from the receiver and sends the audio to the Solaris computer, which has a Real Audio Server.
The long term objective is to set up both receiving and transmitting. Of special interest is the use of Web-transceivers for amature radio satellite operation. Before such a station can be built, there are a number of problems that remain. They include:
The best scheme for tuning signals would be a "sliding frequency window with weighted compression". In this scheme, the server would supply a data stream that represents about 10 times the bandwidth of the desired demodulated signal. For reception of a 2.5 KHz single-sideband modulated voice, the server's data stream encodes 25 KHz of received signal. The 25 KHz is centered on the current settings of the user's controls. The encoded data stream uses weighted compression such that signals near the center frequency have the highest fidelity, and signals farther from the center have increasingly lower fidelity. This scheme has a number of effects. When the user tunes slowly, it feels much like a local radio. We assume the local processor has sufficient compute power to decode the data stream with little delay. When the user tunes more quickly, he will hear signals that, after a delay, improve their fidelity. If the user tunes very quickly and exceeds the passband of the encoded signal, he must wait for the system to catch up.
Implementation of this system would require a specialist in DSP and signal compression. Any volunteers?
Transmission of audio is probably best done with Speak Freely or similar Internet telephone software. Since the source code is available for Speak Freely, it would be possible to modify this program to supply a VOX-like signal for the transmitter PTT.
Existing satellite tracking software can be modified to control antennas. The same software could used to compensate for doppler frequency shift due to the motion of the satellite relative to the receiver's antenna. Integrating this software into the rest of the system is not simple. For example, the R7000 does not have a smooth method of tuning. We are now studying the option of replacing the tuning knob of the receiver (basically a pulse-type shaft encoder) with pulses generated by the computer. This modification would allow smooth frequency control by the computer.
Still under consideration.
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Last updated 18 June 1999