Tests of Winradio Software

This page describes the results of some tests on the demo version of the WinRadio software for the G313 HF receiver. The purpose was to determine the radio's suitability in a mixed Linux/Windows environment. Also described are various sources of radio frequency interference and their elimination.

1. Sending Audio Over a Network

I tested the feasibility of using VNC to remotely control a Winradio over a network using Winradio's software in demo mode. This would allow the radio to be located near the antenna while still being accessed from a remote location. The winradio can be controlled remotely in three ways:

  1. By modem DTMF commands, using a dedicated, optional controller.
  2. Over a network, using the optional Windows-only software.
  3. Over a network using freely-available Linux software to remotely control the Windows machine graphically (VNC and OpenH323).

I only tested method 3.

The setup on computer #1 was:

Software on computer #1:

The setup on computer #2 was:

Software on computer #2:

This setup was designed mimic a functional Winradio. The network consisted of a 100 Mb/s Linksys EFAH05W hub and about 100 feet of Cat-5e cable between the two computers. With this setup, the Windows display shows up as a window on the Linux machine. VNC allows the Windows computer to be controlled remotely over the network, while the audio is also sent over the network using a connection between Microsoft NetMeeting and OpenH323 and is played through the sound card of the Linux machine.

With this setup, the CPU usage of the Windows computer stayed at 100%. Changing to the slowest codec in NetMeeting reduced the load only slightly, so that it varied between 99 and 100%. The system load on the Linux computer stayed between 0.01 and 0.07, jumping up to 0.2 when the mouse was moved in the Windows screen. Despite the fact that the CPU in the Windows computer was being overtaxed, the Winradio display showing simulated noise in the demodulator window was faithfully transmitted by VNC without noticeable pauses. The sound was also transmitted across the network with good sound quality, although there were frequent hiccups. While the tuning knob was being rotated, these hiccups turned into short pauses, and about half the sound was lost. Rotating the tuning knob also caused brief pauses in the demodulator display seen on the Linux side. The network load stayed constant at around 136 kB/sec. When NetMeeting was turned off, the network load actually increased to 160 kB/sec, indicating that the system was CPU-bound but not network-bound. As further evidence of this, by moving windows around on the screen when the sound was off, the load could easily be raised to 1 MB/sec.

However, when the 100 Mb/s Linksys EFAH05W hub was replaced by a 100 MB/s Linksys EZXS16W 16-port switch, the network throughput was reduced to 650 kB/sec, and the WinRadio demodulator screen displayed frequent pauses. This shows that network devices rated for the same speed may have dramatically different throughputs. Normally, Linksys equipment is to be avoided, and a switch from a different vendor would probably not suffer from this problem. (Note: calculating network speed can be tricky, because disk access often limits the observed rates. On my network, the absolute maximum network speed with the EFAH05W hub and two RGL8139's was 6.6 MB/s or 63 Mb/s.)

2. Radio interference from computer network

This section has been moved here .

3. Winradio disk file formats

The WinRadio can scan any region of the rf spectrum and save the spectrum in a disk file, which makes it usable as a rudimentary spectrum analyzer. (There is also a hardware option for 45 MHz IF output for connecting to a dedicated spectrum analyzer.) Although the Spectrum Scope data file format was not recognized by any standard Windows programs, a quick look at a hex dump showed that the file was saved in a simple binary format, with values saved as 4-byte integers. The program below converts the data into a text format (ignoring the text labels and x-axis data): 
    #include<stdlib.h>
    #include<stdio.h>
    int main(void)
    {   
        int i;
        FILE *fp;
        fp = fopen("d.dat", "r");
        while(!feof(fp))
        {
            fread(&i, 4, 1, fp);
            i&=0xffff;
            i=51200-i;
            printf("%d\n ",i);
        }
        exit(0);
     }
Audio files are stored in standard .WAV format and are easily playable on a Linux system (e.g., with wavplay or ecawave).

4. Conclusions

If adequate networking equipment is used, the limiting factor is the Windows computer. If the Winradio is controlled directly from the console, a 1 GHz computer is sufficient. If it is controlled over the network, a computer with a CPU running at least 2 GHz should be used on the Windows side. The software functioned impressively well without crashing or locking up. OpenH323 and Windows NetMeeting communicated flawlessly, as did the VNC client and server. However, graphical network control is not well suited for remote control of a Windows-based radio. The requirement for a fast CPU rules out most currently available notebooks.

By far the largest source of RFI was the computer network. The network produced RF interference in the upper HF band in a radio 25 feet away. To prevent RFI, new networks should use shielded Category 5e cable for all runs, including all patch cables, and networking equipment should be in a metal box instead of plastic. If the remote PC is a laptop instead of a desktop PC, the radio could also be used during a power outage when reception quality is the highest.

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