Svxlink

Svxlink is one great program!  I have been running it since October 2005, and am constantly amazed at just how flexible this package is.  The stock program can be configured as either a simplex link/repeater or as a repeater controller.  Within the basic framework, Svxlink can be configured to act as a "parrot", as an interface to EchoLink, or as voice mail system.  It is fairly easy to extend this functionality using the TCL interface.

I have added a number of functions to my system, such as on-demand local weather information, sysop and emergency paging, automatic Skywarn activation notification, on-demand local information, and on-demand playback of the current ARRL Letter, Handiham e-letter, Newsline, and This Week In Amateur Radio voice bulletins.  New with the latest version is an excessive wind chill/heat index warning, near real-time NOAA weather alerts as parsed by the RSS feed every two minutes, and a cross band link to 29.6 FM.

Future plans for this system include a LiTZ (Long Tone Zero) emergency notification, and a packet radio to voice mail gateway.

My latest changes and additions to the Svxlink system can be downloaded on the repository page.

PC Hardware

Svxlink works quite well with only modest hardware.  My system uses a Pentium MMX 200 MHz processor with 64 MB of RAM and a 2 GB hard drive.  Contained within are three sound cards and a cheap RTL-8139 NIC.  All of the hardware was literally scrounged from "thrown away" PCs, too old to be of much use to anyone -- except for myself of course.

Software

My choice of Linux distributions has always been Slackware, and this system is no exception.  Slackware 10.1 works very well with this system, as does the custom built 2.6.x kernel.  All unneeded services have been disabled, and all unnecessary packages have been removed.  Because of this, and the very low resource utilization of Svxlink, my load average is rarely above 0.05 when idle.

I now use Flite in place of Festival for converting text into voice for the Skywarn and the NOAA weather alert part of the system.  Flite (Festival Lite) is about 20 times faster on my system, which now allows for almost real-time text to voice conversion.  In my opinion, Flite is more intelligible than Festival, even with the default voice.  It certainly is less choppy, and places a far smaller load on my very modest PC.

Radio System

The VHF radio, a Kenwood TM-2550A, was also a "throw away" unit that a friend gave to me.  He had taken it into a nearby ham dealer years ago to have it repaired, and they were unable to fix it.  A few hours with the microscopic schematic in the back of the user manual, a DVM, and hot soldering gun was enough for me to locate a bad solder joint in one of the VCOs in the main PLL.  The rig has been working fine ever since, putting out close to 50 watts into a homebrew 5/4 antenna placed near the top of a pine tree at about the 50 foot level.

I am using a Kenwood TS-430S with the FM option installed for the 29.6 FM cross link.  This rig has not been used for many years, so it just seemed fitting to place it into service in this system.  The rig shows an output of about 60 watts, and is currently fed into a "Windom style" multi-band dipole.

The interface to the PTT and COR of the radio is done with this circuit, which incorporates a three minute watchdog timer.  I built it using mostly junk box parts, which accounts for some of the unusual values.  The values are not really all that critical, with the exception of the RC timing circuit, and perhaps the current limiting resistor for the LED in the 4N25.

To supply power to the interface, I modified my PC to feed +5V on the Receive Data line (pin 2 on a 9 pin connector) of the serial port.  This was actually quite easy to do on my PC.  I used the red wire of a surplus 3.5 inch floppy drive power adaptor and soldered it to pin 2 of the DB-9 connector mounted on the motherboard.