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Thread: Aircraft Scatter Experiments

  1. #1
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    Lightbulb Aircraft Scatter Experiments

    Quote Originally Posted by minilandrover View Post
    Hello i am F5VHZ i have noticed some aircraft scatter in the past but apart from the rapid flutter of signal strength i have not tried any axperiments in long range communication using this method. what frequencies give optimum results and what frequency do you use for calling cq if you do so? regards colin

    Hi Colin,

    Thank you for interest! Airplanes are passive radio wave reflectors which bounce radio signals back to ground greatly extending their range. I am listening to 6 m foreign TV transmitters and 2 m band ham radio beacons through Aircraft Scatter (AS). On 144 MHz / 2 m band the AS doppler shift is about +-200 Hz and on 6 m / 50 MHz band about +-70 Hz.

    The AS flutter/swaying effect is produced by my observations as an interference of direct transmitter (Tx) frequency and the doppler frequency shift of the reflected aircraft scatter signal. I have also found that the momentary 'zero beat' of AS flutter happens at the moment when the plane is crossing the line between Tx and receiving station (Rx).

    If you know with help of flightradar site or ADS-B receiver the position of the aircraft, this AS flutter zero beat effect can be used for direction finding of unknown Tx, for instance. On the other hand, if you know the Tx position, you can tell by the AS swaying zero beat the exact moment when an airplane crosses the line between Tx and Rx.


    Two Way AS QSO?

    Although I have had occasional AS QSO's on 2 m FM for decades ago there are yet very few active AS dedicated hams and I guess none within my range of two radio horizons = abt 840 km, so I have not had any 'real' schedule QSO's through AS. I guess that one could use MS call frecuencies for AS QSO's.

    With help of aircraft locating sites like flightradar24 it is easy to look for an aircraft on course suitable for reflecting signals between two radio stations. If you have a rotatable directional aerial turn it towards the plane and follow its movement with the antenna direction.

    The AS passive radio wave reflection is most intense when the aircraft is near the line between Rx and Tx stations, or above either station. If an aircraft passes above you a simple omnidirectional aerial is enough for observing AS or having a two way QSO through AS reflection. Because most aircraft reflecting surfaces are level, a horizontally polarized aerial is favored. However, if the plane is close to you the AS effect works quite well with vertical aerials, too.


    Beacons and TV Stations

    However, one can easily observe AS signals without help of other active hams. I listen to the 6 m QRP ham beacon OH5SHF with 20 W directive power (ERP) located 243 km away from my Rx station. It can be weakly but clearly heard on CW for a minute whenever a plane passes the line between Tx and Rx.

    The OIRT 1 ch 50.750 MHz Russian 6 m band TV stations are so powerful that they have an AS range of up to the radio horizon of 420 km from Tx-Rx line. They can be heard also through MS easily up to 900 + km away but without the AS doppler swaying/flutter of course. The AS is said to be very clearly visible on upper HF bands, too, but I have not yet tried it.

    Below are some screenshots about Rx and Tx positions and examples of 'Aircraft Scatter Direction Finding' (ASDF) of Tx stations.



    Regards and 73,

    - Juha -


    Links

    A Finnish AS thread with pic captions in English: http://oh7ab.fi/foorumi/viewtopic.ph...295&p=724#p721

    Video about Doppler Shift of Aircraft Scatter on 144 MHz: http://www.youtube.com/watch?v=Iouk8hLckj4

    Video of Aircraft Scatter Wobbling Flutter Sound on 49.750 MHz: http://www.youtube.com/watch?v=ANYf2kcTwME

    PC sound card Audio Spectrum Analyzer "Spectrum Lab" software by DL4YHF: http://www.qsl.net/dl4yhf/spectra1.html#download


    Attached images:

    2012-02-08 49.757.844-1 Flight AFL321 Segezha Nadvoitsy TV Tx Aircraft Scatter Direction Finding Example (c) OH7HJ

    2012-02-08 49750-3 Boeing 747 KAL510 direction finding example of KO59DX St Petersburg TV by crossing Rx-Tx line (c) OH7HJ

    50.033.097 KP30HV Kouvola Kuusankoski OH5SHF 20 W dist 243 dir 170

    2012-02-09 50.033.097-03 An example of using aircraft zero beat interference point for Tx direction finding (c) OH7HJ
    Last edited by OH7HJ; 2012-02-22 at 12:06.

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    Cool Aircraft Scatter 'Comic Strip' Part 1

    2012-02-21

    How do AS signals look like? I have connected my receiver speaker output to a computer sound card and look at it with an ordinary spectrogram software. Here is a screenshot sequence with my comments written on notepad 'speech bubbles' about what is happening on each pic of the example spectrogram 'comic strip'. These should help those interested in AS who might like to learn read and interpret Aircraft Scatter Doppler traces personally.

    A brief intrigue to the cartoon: Unknown plane doppler emerges on spectrogram strip left. Line is thick and the strip background gets dark which tells that the signal is strong and the plane is close. Its bypass somewhere near my Rx station is recorded on the strip. This lets to expect the plane get within flightradar24 range soon, too.

    After a while, the plane emerges on flightradar24. It is recognized as a Boeing 777 on Alitalia flight AZA793 coming from northeast. In the meantime, the plane has moved to the back of my yagi aerial. So I turn the aerial to follow it southwest. Its momentarily lost trace reappears on strip right. To be continued on next message...


    Pics

    Each of my AS screenshot pics is labeled for year-month-date and frequency followed by number of screenshot and finally a description of each experiment.

    Receiving station (Rx) setup like aerial and its direction, receiver and mode is explained on left down corner of each screenshot.

    Here is the first part of the 'cartoon':

    2012-01-21 49750-01 Aircraft Scatter Comic Strip - Boeing 777 AZA783 bypassing emerges at flightradar24 too (c) OH7HJ

    2012-01-21 49750-02 Aircraft Scatter Comic Strip - Unknown close plane doppler visible on spectrogram strip (c) OH7HJ

    2012-01-21 49750-03 Aircraft Scatter Comic Strip - Unknown plane now on its bypass near my Rx station (c) OH7HJ

    2012-01-21 49750-04 Aircraft Scatter Comic Strip - Expecting plane to come within flightradar24 range(c) OH7HJ

    2012-01-21 49750-05 Aircraft Scatter Comic Strip - Plane emerges on flightradar24 as Boeing 777 AZA793 (c) OH7HJ
    Last edited by OH7HJ; 2012-02-22 at 11:40.

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    Cool Aircraft Scatter 'Comic Strip' Part 2

    ... continued from previous message:

    Still another doppler of some unknown approaching plane emerges on strip left.

    AZA793 doppler trace fades out of my range near city of Kotka.

    Last pic shows a 'falling star' - a Meteor Scatter (MS) or an Electric Discharge Scatter (EDS) flash on spectrogram.


    Regards,

    - Juha -


    Pics:

    2012-01-21 49750-06 Aircraft Scatter Comic Strip - Turning aerial to follow AZA793 southwest (c) OH7HJ

    2012-01-21 49750-07 Aircraft Scatter Comic Strip - Doppler of an unknown plane emerging on left (c) OH7HJ

    2012-01-21 49750-08 Aircraft Scatter Comic Strip - AZA793 doppler on right fading near Kotka (c) OH7HJ

    2012-01-21 49750-10 Aircraft Scatter Comic Strip - Meteor scatter fingerprints flashing on spectrogram strip (c) OH7HJ
    Last edited by OH7HJ; 2013-10-24 at 15:50.

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    Hi Juha and Colin.
    I read with interest the reply to Colin re: aircraft scatter. A couple of observations come to mind.

    1) Scatter is often scheduled, especially when the two radio station are contesting (23cms and 13 cms especially) using the AirScout program. The South Birmingham Radio Society (of which I am a member) uses this program.

    2) I admit that from a personal viewpoint it is a bit hit and miss.

    3) There is a school of thought that feels that the signal is using the vapor trail. However, I strongly disagree.
    Why? Well, my reasoning is this (I am a layman and a radio ham, so please forgive any errors here):
    a) The half wavelength (at 23 cms and 13 cms) is far larger than the ice crystals in the vapor trail.
    b) The argument that the hot vapor trail causes an thermal inversion cannot be correct. Why?
    Well, because within an instant the hot gas is frozen within a microsecond after leaving the jet engine. At 30 -40 thousand feet the air temperature is roughly between -40 -50:C, darn cold. Boils Law will go into the details as to why this is the case.

    4) If the thermal inversion theory were valid, then the reflected signal would not flutter, but would be a little like sporadic E.
    The flutter (as Juha correctly states) is a phenomenon of phasing, and as the aircraft moves, so does the phasing change with relation to the aircraft's angle, speed and size, as well as (I do believe) in daylight, a secondary E-layer reflection might occur, again causing a phasing relationship.

    5) Only the aircraft itself can effectively act as the main reflector of radio waves from say 10 metres upwards: the larger the aircraft the lower the frequency that can be reflected.

    I hope my reasoning is valid and correct. I am open to well reasoned argument on this point, and, if I am shot down in flames, then I will say that that is a lesson learned. For the time being the empirical evidence very well stands up to questioning.
    regards and 73 de Tony > g6ypk <

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    Lightbulb

    Quote Originally Posted by g6ypk View Post
    Hi Juha and Colin.
    I read with interest the reply to Colin re: aircraft scatter. A couple of observations come to mind.

    1) Scatter is often scheduled, especially when the two radio station are contesting (23cms and 13 cms especially) using the AirScout program. The South Birmingham Radio Society (of which I am a member) uses this program.

    2) I admit that from a personal viewpoint it is a bit hit and miss.

    3) There is a school of thought that feels that the signal is using the vapor trail. However, I strongly disagree.
    Why? Well, my reasoning is this (I am a layman and a radio ham, so please forgive any errors here):
    a) The half wavelength (at 23 cms and 13 cms) is far larger than the ice crystals in the vapor trail.
    b) The argument that the hot vapor trail causes an thermal inversion cannot be correct. Why?
    Well, because within an instant the hot gas is frozen within a microsecond after leaving the jet engine. At 30 -40 thousand feet the air temperature is roughly between -40 -50:C, darn cold. Boils Law will go into the details as to why this is the case.

    4) If the thermal inversion theory were valid, then the reflected signal would not flutter, but would be a little like sporadic E.
    The flutter (as Juha correctly states) is a phenomenon of phasing, and as the aircraft moves, so does the phasing change with relation to the aircraft's angle, speed and size, as well as (I do believe) in daylight, a secondary E-layer reflection might occur, again causing a phasing relationship.

    5) Only the aircraft itself can effectively act as the main reflector of radio waves from say 10 metres upwards: the larger the aircraft the lower the frequency that can be reflected.

    I hope my reasoning is valid and correct. I am open to well reasoned argument on this point, and, if I am shot down in flames, then I will say that that is a lesson learned. For the time being the empirical evidence very well stands up to questioning.
    regards and 73 de Tony > g6ypk <
    Hi Tony,

    Thank you for interest! AS spotting is a scarce hobby so it is encouraging to learn there are others explaining its features, too! Because tracks of ice meteors are supposed to scatter on SHF, it would at first thought appear sensible to think that also aircraft condensation tracks might scatter on SHF like on 23 cm and 13 cm bands.

    I have myself experimented only on lower bands like 2 m and 6 m. Also my friends have succesfully captured AS dopplers on HF AM station carriers. Further, I have seen screenshots of short but characteristic AS dopplers on MF AM carriers - a large passenger jet is indeed just large enough to act as a half wave reflector on MF. I regularly spot also AS dopplers of low flying prop planes. On these lower than SHF bands, only reasonable explanation to cause the AS scatter is the aircraft itself.

    SHF radar pulses are known to reflect from the aircraft, rather than from their condensation tracks. Radars see planes on medium and low altitudes where there are no tracks. That would suggest that the aircraft itself is a lot larger and more efficient radio wave reflector than its condensation trail is. So no FLAK against your reasoning yet - I would agree with your explanations.

    Also thanks for informing about your special software! Please attach some links for us not familair with it to learn more!


    Is MS in Reality EDS?

    While recording aircraft scatters on 6 m band, I have also been looking how the spectrums of very fast velocity phenomena, like Meteor Scatters (MS), look like. To my surprise, I have not found from spectrums of 'MS' any evidence about fast movement.

    Instead, all the 'meteor scatters' I have studied do have a spread spectrum characteristic of electric discharges. That has lead me to suppose that these VHF 'meteor scatters' might actually be 'Electric Discharge Scatters', which could be abbreviated as 'EDS'. The longer EDS, the higher in atmosphere the high voltage discharge would appear to be, and the more it resembles aurora scatter spread spectrum familiar for us here up North. Explaining further, the discharge might cause a semiconducting local air ionization. Until the ionization cools and fades out in a few seconds, it reflects radio waves like ionospheric layers do.

    I know that trying to replace the familiar explanation of 'MS' with an idea of atmospheric electricity 'EDS' is a heretic thought. Some of these electric discharges might indeed be primed by meteor trails, but I guess most of them start spontaneously as natural atmospheric electricity high voltage purges.


    73, - Juha -

    Attached screenshots of 6 m TV band scatters usually thought to be Meteor Scatters (MS), but actually having the characteristic spread spectrum of high voltage discharges, suggesting that they might actually be caused by high atmosphere Electric Discharce Scatters (EDS).

    2012-12-06-04 Analysis - Dual Segezha - Arkhangelsk - Wide ED scatters on both strips at ts 1259.jpg2012-12-19-01 Arkhangelsk - Nyandoma - Curious long wide multi EDS purring signal again on Nyand.jpg2012-12-06-03 Dual Segezha - Arkhangelsk - Wide ED scatters on both strips - Recording - (c) OH7.jpg
    Last edited by OH7HJ; 2013-10-24 at 19:37.

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    AirScout.zip

    Juha. I am most happy to make my thoughts known. Though I am no expert, not even by any stretch of the imagination. Please find attached the AirScout.zip file. However the complicated way this site handles (I must be dumb) handles attachments puzzles me. The file does not seem to want to attach? I could email the file, though yahoo might not like the file size.

    I have done everything expected, followed the file upload syntax, but still to no avail.
    Any ideas?
    73 de Tony g6ypk



    Quote Originally Posted by OH7HJ View Post
    Hi Tony,

    Thank you for interest! AS spotting is a scarce hobby so it is encouraging to learn there are others explaining its features, too! Because tracks of ice meteors are supposed to scatter on SHF, it would at first thought appear sensible to think that also aircraft condensation tracks might scatter on SHF like on 23 cm and 13 cm bands.

    I have myself experimented only on lower bands like 2 m and 6 m. Also my friends have succesfully captured AS dopplers on HF AM station carriers. Further, I have seen screenshots of short but characteristic AS dopplers on MF AM carriers - a large passenger jet is indeed just large enough to act as a half wave reflector on MF. I regularly spot also AS dopplers of low flying prop planes. On these lower than SHF bands, only reasonable explanation to cause the AS scatter is the aircraft itself.

    SHF radar pulses are known to reflect from the aircraft, rather than from their condensation tracks. Radars see planes on medium and low altitudes where there are no tracks. That would suggest that the aircraft itself is a lot larger and more efficient radio wave reflector than its condensation trail is. So no FLAK against your reasoning yet - I would agree with your explanations.

    Also thanks for informing about your special software! Please attach some links for us not familair with it to learn more!


    Is MS in Reality EDS?

    While recording aircraft scatters on 6 m band, I have also been looking how the spectrums of very fast velocity phenomena, like Meteor Scatters (MS), look like. To my surprise, I have not found from spectrums of 'MS' any evidence about fast movement.

    Instead, all the 'meteor scatters' I have studied do have a spread spectrum characteristic of electric discharges. That has lead me to suppose that these VHF 'meteor scatters' might actually be 'Electric Discharge Scatters', which could be abbreviated as 'EDS'. The longer EDS, the higher in atmosphere the high voltage discharge would appear to be, and the more it resembles aurora scatter spread spectrum familiar for us here up North. Explaining further, the discharge might cause a semiconducting local air ionization. Until the ionization cools and fades out in a few seconds, it reflects radio waves like ionospheric layers do.

    I know that trying to replace the familiar explanation of 'MS' with an idea of atmospheric electricity 'EDS' is a heretic thought. Some of these electric discharges might indeed be primed by meteor trails, but I guess most of them start spontaneously as natural atmospheric electricity high voltage purges.


    73, - Juha -

    Attached screenshots of 6 m TV band scatters usually thought to be Meteor Scatters (MS), but actually having the characteristic spread spectrum of high voltage discharges, suggesting that they might actually be caused by high atmosphere Electric Discharce Scatters (EDS).

    2012-12-06-04 Analysis - Dual Segezha - Arkhangelsk - Wide ED scatters on both strips at ts 1259.jpg2012-12-19-01 Arkhangelsk - Nyandoma - Curious long wide multi EDS purring signal again on Nyand.jpg2012-12-06-03 Dual Segezha - Arkhangelsk - Wide ED scatters on both strips - Recording - (c) OH7.jpg

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