HF Spectrum Monitor Technical Information

Location : Central Southampton, UK

29th August 2011
The HF Spectrum Monitor is now being run directly on the recently updated main web server after a serious motherboard failure on its previous server.


This website offers a live view (see links below) of the HF Spectrum seen on a wideband HF receiver connected to a web server via control and graphing software. The receiver offers an instantaneous snapshot of the full 0 to 30 MHz HF spectrum, as well as continuous filtered data from one of its 4 narrowband tuned channels.

You may select a section of the wideband and set the frequency and bandwidth of the narrowband channel. Spectral displays can be viewed in your browser in real time.

Queries and suggestions may be sent to contact

Note that occasionally some man-made interference (QRM) is seen from nearby IP over mains signalling.

Main Viewer (with live MP3 audio stream)

Main Viewer

Note that the MP3 streaming may not work behind a Proxy/Cache (e.g. at work), and in this case, a small 10s live sample MP3 can be played instead.

[To see if you have the Flash Player (Version 9 or later), click here]
[To download the latest Flash Player click here] (install notes)

 viewer

A separate 24 hour zoom-able waterfall display shows a chosen section of the spectrum built up from snapshots taken at 2 minute intervals over the last 24 hours. Fully zoomed resolution is approximately 380 Hz / bin (windowed).

24 Hour Waterfall Viewer

24 Hour Waterfall Viewer

 waterfall

Hardware and software details

dwr16 This HF Spectrum Monitor is based around a commercial Digital Wideband Receiver. This digitises the antenna input using a 16bit ADC at 80 MHz, providing a wideband signal snapshot together with four 48kHz narrowband tuned outputs. The receiver output is via high speed USB2.
80MHz reference A precision low phase noise crystal frequency reference from Precision Test Systems provides a stable 80MHz clock for the receiver. Although the receiver itself has a good on-board crystal, this reference provides a stable signal with around 0.01ppm accuracy.

web server The receiver is connected via USB2 to the 1U web server (AMD Athlon 5050e Dual Core 2.6GHz with 4GB RAM). This allows multiple users to view the wideband spectrum, and each user may tune one narrowband channel and view a narrowband spectral plot or provide audio output. A separate 24 hour waterfall plot may be viewed and zoomed independently by each user. The server runs SUSE Linux and serves its status pages via a redirect from the main web server holding this content. The connection to the internet is via 4 Mbit ADSL modem / router.

loop The antenna is a 1.1m active loop made by Wellbrook Communications. It is mounted on a vertical metal pole (also used for a washing line) around 2.5m above the ground.

Data collection, receiver control and image generation software is written in "C". The data collection program runs continuously, saving sections of wideband and narrowband data to temporary RAM files. All images are produced using the GD library in PNG format on demand from the user's web browser. The main web page contains dynamic HTML or Adobe Flash viewers that display these graphs and allow receiver control.

Useful links

Wikipedia Affiliate Button