Radarspotting

Hi,

A remote listening post from among bears and wolves of remote Northeast corner of EU! I am in the planespotting not only for long time interest in aircraft but also for ham radio style practical experimenting.

Here is a discussion thread I am writing about distant TV and BC radio station reflections from aircrafts - In other words 'Aircraft Scatter' - using planespotting sites to identify doppler signals with individual planes:

http://oh7ab.fi/foorumi/viewtopic.php?f=21&t=295&p=908#p908

Yet I am to ADS-B with kind supporter 'lend-lease' hardware but also looking for a mode-S receiver of my own for permanent sharing online.


- Juha OH7HJ -

     Finland

A couple of screenshots from Aircraft Scatter experiments with ADS-B identification.

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A still less known radio scatter is that of natural Electric Discharge Scatters (EDS) in ionosphere. These are usually regarded as Meteor Scatters (MS).

However, the EDS have a distinctive spread spectrum of an electric discharge without any doppler evidence of fast movement of a meteor.

I am listening to ED scatters of distant TV transmtters with the same standard ham radio inexpensive hardware as to AS. A couple of EDS examples attached.

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This is a very interesting topic. Particuarly Meteor scatter was something I always wanted to ty.

It's totally new to me that aircraft can also be a sorce of scatter - I would have guessed that the 'target' to small to reflect anything. But all that metal makes a good reflector.

I'd be interested to kept updated on your experiments.

Thank you for interest! Yes, all that metal surface below a long wide wing is a nearly optimal reflector. Quite like a horizontal mirror, the aircraft wing underside reflects radio waves especially strongly further on and towards ground at the same shallow angle as the wave comes. Because the aircraft is moving it causes a doppler frequancy shift to the scattered wave. By this doppler shift a radio scatter is easy to recognize as an Aircraft Scatter (AS).

Like with any other reflection, you get the strongest scatter when the incoming reflection angle is the same as the outgoing reflection angle. That is why the most intense aircraft scatter appears when the plane is near the line between transmitter (Tx) and receiver (Rx). So the best direction to listen to reflected waves is not at the site of Tx - like conventional radars do - but on the opposite side of the aircraft. To this direction, my friend could catch a momentary aircraft scatter from a 0,1 Watt 144 MHz beacon Tx situated 100 km away as the plane was crossing the line between the beacon Tx and his Rx..! 

Fuselage and rudder surfaces are also large so a big aircraft reflects rather well to other directions, too. When listening to powerful VHF BC and TV Tx aircraft scatters I can follow aircaft doppler tracks in best case up to the radio horizon of about 420 km of a high flying plane on FL 300+ .

MS and EDS are very easy to spot on 50 MHz because this band appears to be about the optimal for them. I guess that is because 50 MHz wave reflects already from a rather weakly ionizated spots in high atmosphere, like those caused by Electric Discharges (ED) between layers of ionosphere. 


- Juha -