Hi Folks,I embarked on a little radio science as part of observing the annular solar eclipse that took place on 14th October.
Aim
To evaluate the potential effect due to a solar eclipse upon propagation of the 2.5 MHz WWV between Fort Collins, Co and CM87, located near Menlo Park, Ca
Method
WWV 2.5 MHz was received using an 80 ft longwire antenna suspended at 20 ft, approx NE/SW orientation. Receiving site approximately 600 ft above sea level. Receiver: JRC NRD535 adjusted to 2499 kHz USB, with AGC off and RF gain adjusted for an S-Meter reading of S9 - fixed gain with no risk of receiver overloading. Receiver audio was analysed in Spectrum Lab to calculate a measure of signal strength. The 1 kHz carrier heterodyne (resulting from deliberate off-tuning of the receiver by 1 kHz) was used as a measure of signal strength. A measure of noise from a small "quiet" portion of spectrum was subtracted from the signal measurement to yield a signal to noise figure for WWV reception. Data was recorded at 5 sec intervals, starting before local dawn, approx 1330 UTC until approximately 1900UTC. A companion set of data was recorded 24 hours later to enable comparision between eclipse and non eclipse conditions. During the eclipse event, the path of maximum obscuration passed approximately halfway between the transmitting and receiving locations.
Results
At 2.5. MHz, signals are expected to be subject to significant attenuation by D layer absorption during daylight hours. The onset of dawn is seen as a steady decrease in measured signal in the early range of both data sets. See the attached chart. As the eclipse progressed, there is a marked higher received signal in comparison to the same time the next day. It is to be noted that data is affected by reception of signals other than WWV that were audible on both days after WWV had faded. The effect is noticeable in the great variation in measurements obtained ~ 1500 to 1630 UTC. There is a later (17:30 to 19:00 UTC) smooth periodic variation in measured signal. This variation is offset between the eclipse and non eclipse data set. Additional non-eclipse data would be helpful in understanding this phenomenon, and any relevance to the eclipse event.
Conclusion and Comments
The experiment offers some insight into a particular reception path during the eclipse event. Data was compromised by unexpected interfering signals but still seems to show a clear change in propogation that could be attributed to reduced D layer absorption. A periodic variation in signal strength in the late stages of both observations is of interest and invites further investigation.
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File Attachment 1: Eclipse_Plot.png