Robert J Morton The Graph Area Using the Mouse The + - Buttons Band Selection Centre Frq+Span Signal Updates Source Code

My Radio Band Scope Applet Hits Graph Image

This applet gives a general view of signal activity over a selected portion of the radio spectrum. It is not for serious point to point or 'net' communications work. The graph area shows the strengths of signals (vertical scale) found across the frequency range (horizontal scale).

The frequency scale below the axis is in megahertz (MHz). The vertical axis gives the signal strength. This is numbered in what are known as S-units. Communications receiver S-meters (signal strength meters) are normally graduated from 0 to 9, with a few further graduations given in decibels (dB) above S9. For simplicity, the scale on this graph simply extends up to S12. The signal strength values are arranged so that S0 (S-zero) is the band's ambient noise level.

As you sweep the mouse pointer around within the graph area, the frequency at the mouse pointer (in MHz) appears as a figure at the top of the graph on the right. The signal strength of the actual signal present at the mouse pointer is shown on the signal strength axis at the left of the graph as a yellow thermometer-style indication. If you click the mouse button on a particular signal shown on the graph, the applet can send a command to your receiver (or transceiver) to monitor (listen in on) that frequency. That frequency then appears in yellow along the top of the graph to the left, with the caption Listening on --> pointing at it.

The + and - buttons (above the graph in the centre) allow you to 'inch' the listening on frequency up and down half a kilohertz (kHz) at a time. To tune your receiver more accurately than this - eg to maximise the intelligibility of an SSB signal - it is assumed that you can adjust directly the carrier insertion frequency on the receiver.

The normal intended use of this applet is to monitor (or participate in) activity on one of the established selectable bands. First select the type of band you want from the Select Band Type Choice menu on the right. The Select Band Choice menu below it will then contain the names of all the available bands of that type. Now select the particular band you want to monitor from the Select Band Choice menu. Once you have done this, the following happens:

1. The appropriate band span and centre frequency are selected and the appropriate frequency scale is drawn along the bottom of the graph.

2. The appropriate bandscope data file is loaded from the web server and displayed on the graph.

You now see the signals present on that band at the time the latest bandscope data file for this band was generated. You can now click on to any signal in order to listen in.

If you want to sample a part of the spectrum which is not one of the pre-selectable bands, first select the frequency span you want from the drop-down menu at the top centre of the applet. Then enter the centre frequency of the area of the radio spectrum you want to map. It must contain a decimal point and one decimal digit (which may be a zero). The frequency you enter may be automatically truncated to a value that fits in with the steps used in the currently selected frequency span. If you enter a frequency that makes the minimum frequency too low, the program sets the centre frequency to the minimum permitted for the currently selected frequency span. This will be a little over half the currently selected frequency span. Then press the Update Now button to scope the data.

Signal Data Updates

Whether you are using a preselectable band or a manually selected frequency range, the date and time the current data file was generated is shown along the bottom of the applet panel. Pressing the Update Now button (bottom right of applet panel) causes the a command to be sent to the receiver (if it is currently active) to re-scope the band concerned. The age of the current data is shown just above the Update Now button. This will only work if an appropriate receiver is on and being sampled by the bandscope server program, which in turn is feeding updated files to the web server.

The Update trace... Choice menu allows you to select the frequency with which the bandscope data is refreshed. Again, this will only work if an appropriate receiver is on and being sampled by the bandscope server program, which in turn is feeding updated files to the web server.