HF Spectrum Monitor Technical Information

Location : Central Southampton, UK

This website allows you to connect to and control a wideband software defined HF radio receiver connected to this server. It offers a full 30MHz instantaneous view of the HF spectrum, which can be zoomed to show bands in detail. You have tuning control of one of the receiver's DDC tuned channels. You can view the narrowband spectrum in this channel, and listen to the output of a demodulator via streaming audio.

All the data collection, processing and graph creation is performed on the server, with the browser acting as a display and request interface. The system is free to use and no login details are required. When you load the viewer, you will be allocated a temporary ID that allows you to tune one channel and view the tuned and wideband spectra.

The HTML5 viewer has been tested with Firefox 12.0, Internet Explorer 9.0, Chrome 18.0 and Opera 11.62 (audio stream has extra delays and gaps in Chrome, and seems a little erratic in Opera).

Queries and suggestions may be sent tocontact

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

Main Viewer
(See current 30MHz spectrum, tune and listen live audio)

arrowMain Flash Viewer

arrowMain HTML5 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)


A 7 day 24 hour zoom-able waterfall display shows a chosen section of the spectrum built up from snapshots taken at 2 minute intervals. The "live" page shows data over a rolling24 hours (data from 00:00 UTC to "now" from today, data from "now" to 23:59 UTC from yesterday). Previous days completed spectra may be selected for comparison. Fully zoomed resolution is approximately 380 Hz / bin (windowed).

24 Hour Waterfall Viewer

arrow24 Hour Flash Viewer

arrow24 Hour HTML5 Viewer


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 CentOS Linux. 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

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