andythomasorg - Amateur Radio Astronomy

These are my first efforts in amateur radio astronomy.

Solar noise and the solar eclipse of 11 August 1999

During the 1999 solar eclipse, I was fortunate to be with relatives in Idless near Truro in Cornwall, right under the totality. This was a unique opportunity to cary out experiments in amateur radio astronomy. During the eclipse,the sun was monitored on 11 GHz and 145 MHz, and ionospheric propogation was also studied. Not all the experiments worked! I also monitored relative light level and temperature.

This shows the 145MHz Yagi and the 11 GHz offset dish pointing at the sun.

My solar radiometer is an 80cm domestic satellite dish with LNB into a Scientific Atlanta Ku-band receiver. This outputs the signal strength received as a voltage (up to 5volts) on the AGC output. If you fix the dish pointing into the path of the sun, the voltage rises as the sun transits the beam.

The 11 GHz experiment monitored the blackbody temperature of the sun. Looking at the solar transits in the diagram below (from right to left), position 1 is a solar transit on 10 August 1999, indicating the maximum output. This was a transit of the sun at about 10:35. At this time on the eclipse day, at the height of the transit the sun would be approximately half covered by the moon. This is position 2 on the graph. Monitoring started at 09:57.

Finally at position 3 (10:47 local time on eclipse day) I adjusted the dish to get the maximum voltage and indeed could not get it as high as it had been the previous day. Conclusion: the 11 GHz radiometer showed a 50% reduction in output when the sun was covered by 50%.

I also monitored the solar noise at 145 MHz. In this experiment the absolute level of audio output was monitored, a high voltage indicating noise emission. No significant effect was observed.

At MF (Medium Wave) I monitored the transmission from Radio Nacional de Espana in Northern spain. This was perfectly clear before dawn due to the D layer ionosphere propagating MF signals at night. (did you ever listen to Radio Luxembourg in bed?). At daytime it is supposed to be impossible to receive MF stations at this distance and the hypothesis was that the eclipse would change the D layer to night conditions. However, on the day, there was a great deal of interference on an adjacent frequency, and the results were inconclusive.

To measure relative light intensity I made a very simple circuit comprising a battery in series with a CdS resistor wired to a chart recorder. As the light fell so did the resistance of the CdS cell so there was a higher current flowing across the chart recorder. This is a calibration test made in Market Harborough on 4 August at sunset.

On the eclipse day the pattern was similar at the beginning but then the light fell very abruptly. The discontinuity on the chart below happened in 1 second!

As the eclipse approached we became suddenly aware that it was getting suddenly very cold. This is a chart of the temperature (in degrees fahrenheit) against local time; the full eclipse was at 11:11 local time.

I'll always remember that we suddenly saw the eclipse just after totality for a magical couple of minutes; and how the birds roosted and then flew around in circles; and the cows moo'd in confusion as it became light again.

See also the page about the solar eclipse 2006.

HF (decametric) emissions from Jupiter

Since the 1950s it has become known that Jupiter emits bursts of radio activity in the HF (short wave) bands, with a concentration of energy around 21 MHz. These bursts are described as "short" or "long" and rapidly rise in radio frequency. It's important to get a clear frequency - not easy nowadays - and to listen at times when the bursts are predicted. I listen on 20.480 MHz approx. and I use prediction software sold by Radiosky publishing.

The predictions are based on the position of one of Jupiter's moons, Io, in relation to 3 sites on Jupiter known as A, B and C. The abbreviations used for the emissions are IO-a, Io-b and IO-c. IO-d emissions come from region d but are not related to Io's orbit.

Noise bursts from the interaction of Io and Jupiter are attached below.

I analyse the noise bursts using the program "Cooledit" to remove the noise. You can download the bursts from Jupiter as I have received them, in a short file (18k) of what is left after processing. The order is Io-a Io-b Io-c.

Detecting Meteors

Monitoring radio signals is a good way of indirectly detecting meteors. As meteors burn up in the upper atmosphere they leave a cloud of ionising gas that reflects radio signals. So by monitoring the frequencies of powerful radio broadcasts that aren't usually heard at your location, you might hear a "ping!" of a broadcast reflected by one of these gas clouds.

Usually the broadcast stations in the FM band are monitored in this way. However, having tried out this technique, I am concerned that it is hard to distinguish reflections due to meteors from reflections due to other propogation pheneomena e.g. sporadic ionisation of the E layer (sporadic E). This problem can be compounded with an automatic programe that resets itself after say 5 seconds - if the band is still open on sporadic E conditions then it will be instantly recording another "hit".

A program from COAA Portugal is absolutely superb for this process. You should go to: www.coaa.co.uk/r_meteor.htm
and download the program. If you follow the instructions correctly - included in the program - you can use the soundcard on the PC to show the reflections (of a shortwave radio broadcast station) from the ionised gas clouds swirling around at high altitude.They look like this:

This was my first and very early effort but it is compatible with the images shown in the British journal "Radio Communication" of March 2000. You can also use the program as a passive radar system. Here are the reflections from several airliners out of London Stansted airport (and possibly USAFE Mildenhall!) as they came towards, crossed over, and left from, my location.

My presentation to the 2006 meeting of the BAA Radio Astronomy Group is attached.

Some downloads

AndyThomas.pps