Hams are continually finding ways to mix ham radio with the Internet. The latest mix is a World Wide Web site called the "Listening Post" (http://nihac.info.nih.gov/ listener/listener.html) , sponsored by the National Institutes of Health Radio Amateur Club (NIHRAC). This site lets you control a UHF/VHF receiver (ICOM R7000), and, if you have a sound card with the proper software, listen to AM, CW, FM, or SSB signals on any ham band between 28 and 2000 MHz! From this Web site you can listen to repeaters in the Washington, D.C. area, local simplex operation, and satellites as they pass overhead of the station located in Poolesville, Maryland. In addition, you can eavesdrop on other services, like the National Weather Service and the Southeast Regional Air Traffic Control towers.

As with so many other ambitious ham radio projects, this one began over a mug of beer. Jeff Johnson (N3NPQ) had invited me to his annual Winter Solstice party. We were sitting in his home, which happens to be an Internet domain (jbj.org), surrounded by a room full of Sun unix servers and ham radio equipment. Jeff pointed at his kingdom of hardware and said, "Andy, let’s put a satellite station on the Internet." Over the next 45 minutes I tried my best to convince him that the hurtles were too great to even consider such a task. In the end, I agreed to "investigate" the idea. The first step was to learn satellite operation. The following spring, Jeff arrived at my doorstep with a trunk full of equipment for satellite operation. By the end of the summer I was working the "birds" and having a ball. The next step was to see if we could put a UHF/VHF receiver on the Internet for listening to satellites. Thus, the Listening Post was born.

If you have a computer connected to the Internet with Microsoft Internet Explorer, Netscape Navigator, or similar Web browser, you can visit the Web site and take control of the receiver. If you have a PC running Microsoft Windows (any version past 3.0), a Macintosh, or a unix workstation, you can download software and to listen to the audio output of the receiver. Your computer, of course, must have a sound card and speakers. You will also need to be using a 28.8 K baud or faster connection, although some people report acceptable sound with a 14.4 K baud modem.

Windows and Unix users have two software options for listening to the receiver: Speak Freely and RealAudio. Macintosh users are limited to the latter. Speak Freely is a free program that is used by many people to send their voices over the Internet like a telephone. The Listening Post main Web page has instructions on where to find Speak Freely. To use it, download the appropriate version of Speak Freely (Windows 3.1, Windows 95, or Unix) to an empty directory and then uncompress the file using pkzip for the PC, or gnuzip for Unix. Setting up Speak Freely is very simple and the program comes with very good documentation. Windows users only need execute the speakfree.exe program. Unix users execute the sfspeaker program. It is best to start Speak Freely after you connect to the Internet, but before selecting a frequency on the Listening Post Web pages.

The alternative network audio system for using the Listening Post is RealAudio by RealNetworks. This is a commercial package, but the audio decoder, RealPlayer, is free from their Web site (http://www.real.com). If you have a Web browser installed on your computer, the RealPlayer will recognize your browser and add itself as a "plug-in". Once it becomes a plug-in, the RealPlayer will start automatically when you click on the proper icon at the Listening Post site.

There are several different Web pages for controlling the Listening Post receiver. The main Listening Post Web page has one method of control and serves as a gateway to the other control Web pages. The main Web page has a simple operator interface that will work with just about any Web browser. You must use the Speak Freely application to hear audio from this page. If you would rather use RealAudio, click on the RealAudio icon for a similar Web page designed for use with the RealPlayer. If you have a Web browser that supports Java applets, you can click on the coffee cup on the main Listening Post page and enter the Java-enhanced Web page for controlling the receiver; this Web page supports both Speak Freely and RealAudio.

I will first describe the operation of the main Listening Post Web page, then discuss how the other control pages differ. The main Listening Post Web page allows you to control the receiver in a couple of different ways. Figure 1 shows one way: preset "frequency buttons". A mouse click on one of the frequency buttons will tune the radio to the frequency listed on the button. The frequency buttons are in a table that also has information about who uses each frequency. In the case of local repeaters, the table includes entries for the repeater, the repeater callsign, and the individual or club that operates the repeater. In some cases, a club has its own Web page, so clicking on the club name will take you to the club’s Web page.

Clicking on one of the frequency buttons initiates two processes. First, it sets the receiver’s frequency. Second, it directs a digitized data stream, containing the receiver’s audio, to your computer. If you have Speak Freely running, the audio from the receiver should arrive at your computer a few seconds after the request reaches the Web server. Your browser will then display a new Web page that tells you that your request has been received. If your request failed for some reason, the displayed Web page will explain why. A "return" option will take you back to the Listening Post page after you have read the message. If all goes well, an icon will appear in the Speak Freely window, and you will hear the receiver’s audio on your computer. If you have chosen a quiet repeater, you may hear nothing but a slight hum. Regardless, you should still see an icon in the Speak Freely window. Changing frequency with the frequency buttons is simply a matter of clicking on a different button. The audio will usually give a squelch burst just as the receiver changes frequency.

When you are done listening on the main Listening Post page, it is very important to click on the DISCONNECT button at the bottom of the Web page. If you do not disconnect, the audio server will continue to send you Speak Freely audio data even if you turn off your Speak Freely program. Since the audio data requires a high bandwidth, your Internet connection will be slowed substantially until you disconnect.

Figure 2 – Manual frequency entry form and DISCONNECT button. You can enter a frequency and select a modulation mode to receive stations not preprogrammed into the frequency select buttons. The DISCONNECT button is used to disconnect from the Speak Freely audio data server.

There is a Manual frequency entry form to access frequencies not listed on the frequency buttons. Manual frequency entry is almost as simple as using the frequency buttons. Figure 2 shows a one-line form near the bottom of the main Listening Post page. This form is a labeled "Frequency (in MHz)". Type a frequency in here. Then click on one of the four buttons labeled: FM narrow, FM wide, AM, SSB (USB) to choose a mode. Finally, click the Set Receiver button. At this point operation should proceed as it did with the preset frequency buttons. Once again, don’t forget to use the Disconnect button when you are done listening.

If you chose to install the RealPlayer on your computer, you can switch to the RealAudio-enabled Listening Post page by clicking on the RealAudio logo at the top of the main Listening Post page. When you arrive, you are immediately greeted with another RealAudio logo. Click on this new logo to start up the RealPlayer. In a sense, RealAudio is the opposite of Speak Freely. You must click on the logo before using RealAudio and you must click on the Disconnect button after you use Speak Freely. Otherwise, using the two audio systems is quite similar. Once the RealPlayer is up and running, click on the buttons or enter frequencies in the manual entry form, just as you would on the main Listening Post page.

Figure 3 – Java control applet. This applet can be found on the Java-enhanced page. It has all the functionality of the other two control pages, plus a status line and a method to step-up and step-down in frequency. Your Web browser must support Java to use this applet.

If your Web browser supports Java, you can use the Java-enhanced control page shown in Figure 3. To access the Java control page, click on the steaming coffee cup at the top of the main Listening Post Web page. After a few seconds of loading time, the Listening Post control panel appears. The top "status" line of the control panel shows the frequency and mode of the receiver. It also shows the IP address of any user connected to the site with Speak Freely. The status display is designed to update automatically every 10 seconds. Just below the status line are a pair of buttons that allow you to select between Speak Freely and RealAudio sound. If you select Speak Freely, there is a Disconnect button displayed as well. Below the Disconnect button is a "list box" of frequencies. Double click on one of the frequencies. The receiver will tune to that frequency and audio will be sent to your computer. You should see the status line update soon thereafter. To manually enter a frequency, go to the entry box at the bottom of the control panel. Enter a frequency (in MHz), choose a modulation mode by clicking on AM, FMn, FMw, or USB, then click on the Manual Enter button.

The Listening Post control panel on the Java-enhanced page has an option not available on the other Listening Post pages. The control panel has frequency step-up and step-down functions. Set the step size in MHz by entering a value into the field at the bottom right corner of the control panel. For example, a value of .0005 would give you 500 Hz steps. Then, click on either the up or down button to step the receiver. In the current configuration the radio gives a squelch noise after each step: a somewhat annoying bug.

The Listening Post is an experiment. As the experiment progresses we will add new features and make various architectural changes (see below). The Listening Post It is not a professionally-designed Web site intended to attract users. Instead, it is supposed to test ideas and encourage hams to investigate how the Internet can be used by radio amateurs. It will have many limitations and shortcomings. We welcome comments and we try to be helpful, but we cannot spend much time helping people sort out problems. Here are a few tips to try if you are not having success with the Web site.

• Erratic behavior

At the moment, only one Speak Freely user can listen to the audio at a time. Up to ten people can listen to the RealAudio data stream simultaneously. One potential problem is that up to ten people can connect to the control pages at one time. Thus, two or more people could interfere with each other trying to access the Listening Post. As currently configured, the user who most recently selected a frequency is the one who gets the Speak Freely audio data stream, and determines the receiver’s frequency. Users could easily end up wresting the audio away from one another as they each click on frequency selections. This tug-of-war is more obvious for those users who are using the Java-enhanced control panel, since these users will notice different IP addresses being flashed on the status line. The two keys to dealing with the potential tug-of-war problem are: 1) understanding how it works and 2) courtesy.

• No audio

If you are a bit too hasty setting up the Speak Freely program, you might not hear the receiver. The help menu in the Windows version of Speak Freely has tips for testing your Speak Freely setup. I especially recommend doing the "echo-back server" tests. RealAudio is a very popular program. If you need help setting up RealAudio, there are many tips and suggestions at the Progressive Networks Web site. There are many Web sites that stream sound with RealAudio, so you will have no trouble testing your RealAudio setup.

• Poor audio quality

Good audio quality requires a fast enough Internet connection and a fast enough computer. Even if you are using a 28.8 k baud modem, check to see that you are connecting with your Internet service provider at some speed over 19 k baud. A poor phone connection will make a 28.8 k baud modem operate at much slower speeds. If you have other Internet traffic while you are listening to the Listening Post, like trying to retrieve your email, you are likely to mess up the audio. Finally, if you are using a 386 computer, chances are the computer is not fast enough to decode the compressed audio stream.

• Your IP address is "not allowed"

The Listening Post has provisions to lock out the IP addresses of people who misuse the site. Most Internet services "rotate" IP addresses, so a whole block of address must be disabled to keep certain individuals out of the system. You may get locked out if you happen to use the same service provider as such an individual. We are sorry for anyone who gets locked out for this reason, but there is not much we can do about it. You are welcome to email us to let us know that you have been locked out.

• RealAudio Player says the file cannot be found

Sometimes the RealAudio Encoder computer crashes. This will result in a file not found error. Either check back on a different day, or try using the Speak Freely method of listening.

• Control panel status line will not update on Java-enhanced page

If the Java control panel status line does not update, try using the "reload" function in your Web browser, also called the "refresh" in some browsers, to force the display to update.

The radio receiver on the Listening Post is an ICOM IC-R7000 located in an office (North Latitude 39.07.532' , West Longitude 077.28.496'). The receiver connects to a commercial discone antenna (WB-1300) on a 25 foot mast. The receiver has a frequency range of 25 MHz to 2.0 GHz, with a small dead spot just above 1.0 GHz (1.0 to 1.025 GHz). It supports the following modulation modes: AM, wideband FM, narrow band FM, and SSB. SSB sideband selection is done by a rear-panel switch, which is always in the USB (upper sideband) position. The IC-R7000 has 100 memory channels, multiple scanning modes, front-end attenuator, infrared remote control, and loads of other features not used by the Listening Post.

Figure 4 – Block diagram of the Listening Post. The IC-R7000 receiver is shown on the bottom left. It’s audio feeds two computers for conversion to digitized audio data streams. All the other signals are network (digital) signals.

Figure 4 shows the general architecture of the Listening Post. The receiver (lower left corner of Figure 4) is connected to the serial port of a Pentium PC via Icom's CI-V Level Converter for controlling the frequency and mode of the receiver. The audio output of the R7000 is spit and sent to two other computers. I will first explain the control aspects of the Listening Post.

The Pentium PC connected to the CI-V Level Converter is running Red Hat Linux 4.0, an excellent version of Unix that can be obtained free over the Internet. The Linux operating system operates the Web server. Web server requests come from the user through the Internet. The Web server requests for controlling the radio are handled through HTML (hyper-text markup language) forms or the Java control panel applet. These requests initiate CGI (Common Gateway Interface) programs written in the Perl 5 programming language. The CGI programs accept requests for frequency/mode changes, provide feedback to the requesting browser, keep logging files, and issue unix shell commands to the operating system. One of the shell commands runs "icom", a nifty little control program by David Mills (W3HCF) at the University of Delaware. The icom program recognizes many different model Icom radios and allows unix hosts to control them via the serial interface. Other shell commands relay requests to the audio server, which sends digitized audio data to the user’s computer. This audio server is a Sun Microsystems SPARCstation 20 running Solaris 2.6. The audio server either compresses audio with Speak Freely and broadcasts that data to the user, or it accepts already compressed RealAudio data and broadcasts the RealAudio data to the user. Since RealAudio employs a sophisticated sound compression scheme, it requires a dedicated computer just to encode the audio data stream. For RealAudio encoding, we use using a Pentium running Windows 95.

The Listening Post is just a waypoint in the long sojourn to a Web-operated satellite station. Not long ago I tried using the Listening Post to hear a satellite (RS-15) during an overhead pass. The changes in Doppler shift of the bird and the rather crude methods of tuning available on the Listening Post made tracking the frequency of a signal cumbersome. Thus, the next step will be to incorporate a satellite tracking program into the Listening Post software to automatically compensate for the Doppler shifts of a received signal. New control buttons on the Web page will have satellite names. These new buttons will be active only during a satellite pass. When you select a satellite button, the Listening Post will check your receive frequency and do Doppler compensation based on the Keplarian data for that satellite. The same tracking software will handle automatic positioning of steerable beam antennas. Our final hurtle will be the problem of remote transmitter operation. Stay tuned!

The current web server is not at its permanent internet site. It will be move to another site sometime in the near future. When the web internet address is changed, information about the new web address will be left posted on the old address. Note also, we do not claim exclusive rights to the name "Listening Post".

Some frequencies, like cellular phone frequencies, have been "locked out" and cannot be accessed from the Listening Post. In addition, all transactions are logged. We keep records of who (i.e. what IP address) has selected what frequencies. Please do not use the Listening Post if this record-keeping raises privacy concerns that are uncomfortable for you.

Pkzip is a file compress/uncompress utility. It is widely available on the internet. Shareware versions of Pkzip can be downloaded from the Pkware web site: http://www.pkware.com .

Gzip is a file compress/uncompress utility licensed by GNU. It is similar to Pkzip, but the license stipulates that anyone can use it for free. Gzip can be downloaded from many internet sites, e.g. ftp://wuarchive.wustl.edu/systems/gnu/ . See the GNU web site ( http://www.gnu.ai.mit.edu/software/software.html ) for more information.

The RealAudio RealPlayer plug-in can be downloaded from the RealNetworks web site at: http://www.real.com .

The IP address is the address of your computer while it is connected to the internet.

According to the IC-R7000 Service Manual, CI-V means: Communications Interface-V.