reflections, echo's, doppler , libration and scintillation

VK3UM GippsTech 2014

Reflections, Echo's, Doppler, Libration and Scintillation.

• The strange.• The unusual.• The down right weird.• Some stuff you may have missed ?• But all have a reason and a cause!


Reflections• From unknown sourcesOnly once .. December 1985 on 432MHz when working the US during the ARRL contest I, and others received ‘1 second echo’s’ from something big between us and the Moon. It lasted for about 20 minutes. Extensive ‘enquiries’ failed to reveal its source. Nobody new ‘nutting’• From orbiting objectsGraham ZL3AAD and I worked during the 80’s, on 432 MHz, both CW and phone via MIR. Others now have recently used the ISS. How about trying it ? Use a low orbit pass for easier tracking. At least now you know precisely where it is.


Echo's

• From known geostationary objects

I have tried, whilst at SM2CEW QTH, to get echo’s from some of the large geostationary Eu satellites running > 1kW to a 6.5M dish on 1296 MHz without success. It should be possible with a bit more EIRP?


Doppler• It is may not be what you first believe?

Max Doppler

Doppler at Moon set

The Moon has actually come closer

to the Earth


Libration• Use it to your advantage


1296 MHz3 Hz wide

1296 MHz20 Hz wide


What is Ionospheric Scintillation?Ionospheric scintillation is a rapid fluctuation of radio-frequency signal phase and/or amplitude, generated as a signal passes through the ionosphere. Scintillation occurs when a radio frequency signal in the form of a plane wave traverses a region of small scale irregularities in electron density. The irregularities cause small-scale fluctuations in refractive index and subsequent differential diffraction (scattering) of the plane wave producing phase variations along the phase front of the signal. As the signal propagation continues after passing through the region of irregularities, phase and amplitude scintillation develops through interference of multiple scattered signals.

http://www.ips.gov.au/Satellite/6/3


When and where does Ionospheric Scintillation occur?Ionospheric scintillation is a well-known phenomenon that has been studied extensively in the past yet it remains a difficult phenomenon to predict or model on a large scale. Scintillation is caused by small-scale fluctuations in the refractive index of the ionospheric medium which in turn are the result of inhomogeneities. Inhomogeneities in the ionospheric medium are produced by a wide range of phenomena (eg plasma bubbles), and those responsible for scintillation occur predominantly in the F-layer of the ionosphere at altitudes between 200 and 1000km. The primary disturbance region, however, is typically in the F-region between 250 and 400km. E-layer irregularities such as sporadic-E and auroral E can also produce scintillation but their effect on L-band GPS signals is minimal.Ionospheric scintillation is primarily an equatorial and high-latitude ionospheric phenomenon, although it can (and does) occur at lower intensity at all latitudes.


What is the Impact of Ionospheric Scintillation? (in short)Ionospheric scintillation affects trans-ionospheric radio signals up to a few GHz in frequency and as such can have detrimental impacts on satellite-based communication and navigation systems (such as GPS-based systems) and also on scientific instruments requiring observations of trans-ionospheric radio signals (e.g. radio-astronomy).


In terms of geographic (geomagnetic) distribution, ionospheric scintillation generally peaks in the sub-equatorial anomaly regions, located on average ~15° either side of the geomagnetic equator, as can be seen in Figure 1, below.


Scintillation• Have I run across something ‘new’ ?• Date … 31st January 2014. from 2210z to 2235z


• The 432 MHz CW signal from K2UYH sounded just like Aurora.• My returned echo (CW) sounded just like Aurora.• but without the ‘frequency shift’ characteristic of Aurora.• However my signal at K2UYH was perfectly clean with no sign of Aurora through out this entire period.• I tried again 2nd March when relationships were similar but the effect was not present noting that the intensity (TEC) was not as great.• with the help of Ron VK3AFW and others, calculations indicated the high probability of actually firing through the ‘bubble’ during that period.• But why did Al K2UYH not hear the effect is the nagging question.• Sure Al was not beaming through the bubble but was hearing my signal via the bubble when reflected direct from the Moon.• The effect stopped almost immediately but preceded with a few partial clean echo’s over approximately a minute.• All then returned to completely normal. 23cm Echo’s were normal.

• Weird .. The coincidence of the alignment of the Moon and the ‘bubble’ with the TEC intensity is a rare situation.

The effect


Noting that the TEC map was recorded an hour later than the period of the observed anomaly, the ‘bubble’ would have been a little further East than shown.

If you do the sums there is a very close collation to the signals passing through the bubble.

It was quite a chance encounter given the position of the respective elements.


ANY QUESTIONS PLEASE ?

reflections, echo's, doppler , libration and scintillation

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