features : Eclipse Monitoring 15th January 2010
by G. Victor A. Goonetilleke
From COLOMBO, Sri Lanka. As most people would know there was an Annular Eclipse of the Sun which was observed between South India and the Northern half of Sri Lanka. While many viewed the eclipse through shaded /smoked glass, Xray papers and many other devices, I viewed the eclipse from my home at Piliyandala (18km SE from Colombo) through the dials of my radio receiver, inside my shack with headphones on staring at the S-metre while scanning the Medium Wave and Shortwave frequencies below 7 MHz. My brother Ron 4S7RO and myself (4S7VK) made a similar observation somewhere in 1984 around 2.30 p.m. in the afternoon with tremendous results. Unfortunately, most of the stations that we observed on 2-7 MHz range, have now left short wave and thus there was very little to observe there. The 1984 Eclipse which ran across Central India gave us HF/SW signals from longer distances compared to the January 15th Eclipse which was only about 100 km north of Colombo. The problem with sky wave is that there is a dead zone between the ground wave and the first hop when we are so close to the eclipse.
What happens during an Eclipse?
Since the amount of sunlight and with it the amount of solar radiation that falls on the ionosphere will directly affect the ionosphere, an eclipse of the Sun where the moon blocks the solar radiation that falls on the ionosphere will bring about a temporary night-time condition during a total or partial eclipse period. While the total or annular eclipse will be preceded and followed by a period of semi darkness the ionization in the eclipse path will be less than on a normal day. As such, radio signals which bounce off the ionosphere will behave differently during an eclipse as the density in the F layers which refract HF signals are different from that of normal day.
Another important change is the disappearance of the daytime D layer. As you know the D layer absorbs low HF radio signals. Therefore, an eclipse, which occurs during daytime, will enhance low band HF MW and LW signals while it will also bring down higher end HF signals.
Taking the above into consideration and past Eclipse monitoring sessions I was getting ready to transmit and also listen to signals during the eclipse period. Unfortunately the unexpected demise of my XYL's brother did get in the way as the funeral was fixed for the 16th. However, with great difficulty I was able to listen between 0800 (1.30 p.m.) when the maximum eclipse phase was ending at 0845 UTC. This was followed two days later with a listening session at the same time to the observed stations, followed by two more days of repeating the exercise. The results were overwhelming to say the least.
Observations on Medium Wave
Usually on the Medium Wave Band the only signals I hear are 720 Chennai, 936 Tiruchirapalli, 1161 Trivandram & 1197 Thirunelveli which are about 700 kilometres away, but during the eclipse many others were also heard which are impossible under normal circumstances. The regulars were very strong during the eclipse and gradually started to drop off after the maximum eclipse had passed. The most exciting MW signal was from AIR Vijayawada 1025 kilometers away.
0800-0810 UTC (0130-0140 PM Sri Lankan Standard Time) Freq Txer Time RST (subsequent days) Comment 720 Chennai 56 (222) Very good signals 837 Vijayawada 222 (000) weak barely readable 900 Kadapa 56 (000) 936 Tiruchirapalli 59+ (53) 999 Coimbatore 56 (000) 1161 Trivandram 56 (222) 1197 Thirunelveli 59+ (54) 1215 Pudducheri 57 (000) 1269 Madurai 56 (000) 1377 Hyderabad 43 (000) mx identifiable 1449 Maldives 33 (000) 1602 Udagamangalam 22 (000) Mx readable
The first RST figures are for the eclipse time, and in brackets subsequent days monitoring. (000) Indicates no signals observed.
The above Medium Wave stations are all across the eclipse zone with the exception of Tirunelveli which is within and the Maldives of course South of Sri Lanka and not propagating across the eclipse zone. However since the Linular Eclipse commenced at 11.16 and ended at 1510 SLT (0546-0940 UTC) the effects on the ionosphere commenced at 11.16 a.m. therefore reception due to the eclipse would change during this entire period with the maximum effects noted during the maximum eclipse time and just afterwards.
HF/Short Wave Conditions
If MW was exciting, low HF/SW signals were staggering. Take Bhutan for example, which is impossible to hear on a normal day but during the Eclipse reception was amazing with English news at 0800 and as we approached 0815 I could follow the program with ease. The strongest signal was Myanmar on 5915 which is just usually a detectable BFO carrier, but reached a staggering 59+ signal and held on for more than 45 minutes. The most exciting catch however, very surprisingly, was the Defense Forces station from Myanmar in Taunggyi on 5770 rated at 10kW starting at 0830, which according to WRTVH 2010 just arrived in my shack is from 0730- 0930.
Although the maximum eclipse slot for Sri Lanka was 0750-0800 UTC, as the eclipse shifted eastwards signals from China started to come in in-strength. It was fascinating to see that Thimpu Bhutan was stronger than Jaypore in Orisa because the refraction point between Colombo and Thimpu was in the eclipse a little earlier than Jaypore and Colombo showing how Thimpu was initially stronger and giving way to Jaypore a few minutes later. Lhasa Tibet was also very strong on 6110 kHz while the same programme on 6130 also listed as Lhasa was weaker.
0800 UTC 5990 CHN 22 (000) 5915 BRM 58+ (000) 5965 MLA 54 (000) 6035 BHU 22 carrier+ (000) 6110 Tibet 33 music (000) 6130 CNR 33 //Tibet (000) 6175 MLA 33 EE News(000) 0815-0820 UTC 5935 CNR? 23 6035 BHU 53 6040 AIR 532 weaker than BHU 6050 MLA+ 22 Heterodyne 6110 TIBET 55 Great signal //6130 233 0815 UTC 5990 23,2/3 CNR 5975 22 station starting to come in 5965 MLA 32 MLA 5915 BRM 59+ unbelievable sigs 6035 BHU 55 6110 TIBET 58 //6130 0830 UTC 6040 AIR 59 6035 BHU 32 barely audible 6030 CNR 22 6020 SEAsian 22 5990 CNR? Only BFO carrier 5975 ?? 22 5965 MLA 32 5935 CNR 32 5915 MYN 59+5 5770 MYN 53 not heard at 0800,0830 special BC for the Eclipse? 6145 CNR 32 7060 VU3ITI 59 for me his signals 56 Bangalore 7060 VU3YFD in Tiripur both-ways 59+
at 0830 on subsequent days nothing was heard on the 6 MHz bands other than a very weak AIR Japore on 6040.
It was a great and amazing experience to observe signals coming up as the eclipse progressed and then to see the signals fading out as we got out of the eclipse.
Receiver & Antenna
The receiver used for the experiment was an Icom R71A communications receiver with an 80 metre dipole at 45 feet above ground. The antenna is non resonant on 6 MHz but is much better than a random wire. An experiment like this should ideally be conducted in an electrically quiet area with a good receiver and a reliable antenna. A well calibrated S-metre or field strength metre will give even more accurate results. I was most disappointed that I couldn't find the time due to my son's wedding a few days earlier and the death in the immediate family to set up more listening posts and set up skeds with radio amateurs. I had two contacts with Indian radio amateurs VU3ITI in Bangalore and VUYFD in Trichur which indicate definite enhanced signals. I informed members of the RSSL some days before and I understand Naren 4S7NC was able to do some observations making some contacts on 40 metres with India.
I hope the above article will create an awareness about propagation during an eclipse and help interested radio enthusiasts to have a better understanding of radio propagation. Since a single hop on HF covers nearly 4000 kilometres even if an eclipse occurs 2000 kms away a radio enthusiast will still be able to enjoy seeing the results on his radio receiver and via two wave HF communications. The ideal is to observe single hop propagation, but even if the eclipse takes place thousands of miles away you will still be able to carry out experiments but you will need to have a professional understanding and also equipment for it to be a meaningful and scientifically successful experiment.