Aircraft Scatter - Lentokoneheijastus ja sen doppleri.

A wide spectrum R1 TV channel slow strip from returning by a route a little different to arrival. In the beginning unstable urban city noise governs the radio spectrum background. Then there are again the already familiar black sections of deafened receiver at the same places as during arrival trip. Probable reason for one of the receiver blackouts is the BC-FM broadcast tower strong RF field.

Background interferences gradually settle down when driving through less populated environment, with an exception of the car onboard a ferry. The open lakeside together with steel deck of the ferry appears raise background noise and interference levels.

Aircraft scatter dopplers are visible as slant lines on the St. Petersburg TV carrier at about 17:12, 18:08, 18:12, 18:23 and 19:08. Parallel to carrier sets of vertical lines are TV 50 Hz side bands. Short sideways spreading marks on many TV carriers are natural scatters like EDS of high sky lightnings. Continuous wandering unstable interferences are coming possibly from car electronics. Time stamps are Finnish local.

The spectrum strip attached is combined from two separately analyzing Spectrum Lab windows. First window at left plots the lower R1 TV channel spectrum through left audio channel and the right SL window plots upper spectrum from right audio channel. Return track on map was created online from an APRSdroid software installed to a GPS equipped android mobile phone.

Examples of meteor scatter ‘head echo’ dopplers captured by Esko OH2AUP from live ‘radar voice’ of OH7HJ R1 TV channel online streaming receiver. The receiving setup of this experiment is a 4-element almost omnidirectional 50 MHz horizontal dipole array with an RTL receiver and SDR Console V3 software streaming a 22 kHz wide TV channel spectrum as two wide band USB sound streams divided to both stereo channels of single MP3 online voice audio channel.

The fast sweep multi TV carrier spectrums by Esko show meteor scatter (MS) narrow dopplers scattered from the very fast velocity of meteors striking down to upper atmosphere and creating ionized trail which scatters TV carriers of 6m band R1 TV channel. Some of the MS doppler pics show meteor dopplers simultaneously on two TV carrier frequencies.

These actual MS head echo dopplers are rather weak which makes it difficult to capture them on low power radio beacons. With high power beacons like these TV carriers meteor dopplers are much easier to spot. Their usual spread spectrum ‘tails’ following meteor head echo dopplers are strong and long lasting which makes the electric discharge tail scatters very easy to capture compared to head echo dopplers of actual meteors.

However, these natural ionospheric electrostatic discharges alone are not necessarily evidence of actual meteor hits. Also, not all meteor head echo dopplers trigger these spread spectrum electric discharge tails. Natural high sky electric discharge scatters (EDS) occur all the time and vast majority of them appear lack any evidence of meteor head echo dopplers. This suggests that most of these longer than MS head echo doppler lasting natural ionospheric discharges are ignited spontaneously, possibly by voltage of naturally accumulating atmospheric electrostatic charge exceeding threshold level of ionospheric electricity discharge.

Meteor Scatter Spectrum Strips

Esko tells that the attached pics are copied with a single audio channel spectrum software so the lower and upper R1 channel TV carrirers show on the same MS strips. Fortunately they overlap so they can be spotted.

These strips do not have frequency or time scales but his fast registered strips have a sweep of 43.066 Hz per pixel and zero beat is the low edge os the strips representing freqs 49739 and 49755 kHz. Middle registered strips are 4 times slower.

For example, the highest strong carrier of this middle registered MS strip is St Petersburg TV and below the center one with many EDS is Moscow TV. Near low edge is Syktyvkar TV: midle20180227060100_20180227060739 - 7000 - 12000 Hz - MS doppler up left - MS head echo dopplers from online live OH7HJ radar stream captured by OH2AUP.gif

Online Radar Voice

The online multi-static radar voice is freely available for online listeners of AS dopplers as well Es and Aurora scatter or MS spotters. Lower R1 band is on left stereo cahnnel and its audio zero beat is 49739 kHz. Higher TV band starts at 49755 kHz zero beat and it is on right stereo channel.

The sound can be picked up from standard web browser through a virtual audio cable software like VB-Audio Cable by setting it as ‘Default Audio Device’ on windows playback devices menu. Then the virtual cable is selected as input audio device for the sound spectrum analyzer software you prefer. Set it listen to left stereo channel for low R1 TV band carriers and to right stereo channel for high band carriers.

These streams are rather easy to spot by anyone familiar with audio spectrum analyzer software like Spectrum Lab. Please ask me for ready Spectrum Lab INI or USR setup files for either wide band R1 carriers or for detail strips of each TV carrier.


‘Radar voice’ is available online at MPnet multi-static radar demo page:
DL4YHF’s Audio Spectrum Analyzer Spectrum Lab download:

Spotting MS from among ED scatters - 1: Aircraft Scatter - Lentokoneheijastus ja sen doppleri.
Spotting MS from among ED scatters - 3: viewtopic.php?f=21&t=295&p=2498#p2498


More of Esko’s MS head echo dopplers captured from the live audio radar stream are attached below.

For listeners of the online ‘radar voice’ of R1 TV channel carriers here are appx. audio frequencies for some easily visible TV transmitters from the stereo audio stream to help with configuring spectrum analyzer software for remote monitoring with one’s home computer:

URL of ‘radar voice’ stream:

Left Stereo Channel

  • Arkhangelsk and Cherepovets TV 590 Hz
  • Kirov TV 1890 Hz
  • Sekezha Nadvoitsy TV side band 3170 Hz
  • Syktyvkar TV 7100 Hz
  • Moscow TV 8420 Hz
  • St. Petersburg TV 10985 Hz
  • Segezha Nadvoitsy TV 18825 Hz

Right Stereo Channel

  • Segezha Nadvoitsy TV 2825 Hz
  • Nyandoma TV 5400 Hz

Please notice that there is some time delay with the online internet audio transfer. I am not skilled enough with sound streaming software to make it transfer time codes. Advice with exact streaming software is appreciated!

True frequencies for some TV transmitters

  • Arkhangelsk TV, LP04GN, freq 49739.583 kHz.

  • Cherepovets TV, KO89WD, freq 49739.586 kHz.

  • Moscow TV, KO85TT, freq 49747.413 kHz.

  • St. Petersburg TV, KO59DX, 49749.975 kHz.

  • Kotkozero TV, KP61OG, freq 49749.998 kHz.

  • Malozhma TV, KP94DD 49755.187 kHz.

  • Suoyarvi TV, KP62EC, freq 49750.016 kHz.

  • Ruskeala TV, KP51HW, freq 49757.806 kHz

  • Segezha Nadvoitsy TV, KP73CW, 49757.818 kHz.

  • Nyandoma TV, LP01CQ, 49760.401 kHz.

  • Juha
    fast20180227060254_20180227060431_crop - MS doppler above two TV freqs - MS head echo dopplers from online live OH7HJ radar stream captured by OH2AUP.gif
    fast20180227074031_20180227074210_crop - Two MS dopplers - Second on two freqs - MS head echo dopplers from online live OH7HJ radar stream captured by OH2AUP.gif

First pic shows a downwards in frequency shooting momentary doppler is distinctive mark of a meteor scatter (MS) head echo doppler. Usually but not always the MS head echo dopplers are immediately followed by a ‘tail’ with only little or no doppler shift. Instead of shift, these ‘tails’ have a spread spectrum.

The spectrum spread is a characteristic mark of radio waves scattered from air ions accelerated by electrostatic discharge. One may suppose that high atmosphere spread spectrum scatters are created by atmosheric electricity. Usual causes of these electric discharge scatters (EDS) appear to be high sky lightning discharges.

On second pic appear to be two MS head echo dopplers after each other on Kirov TV freq triggering immediate EDS’s scattering sets of 50 Hz side bands that almost hide the actual meteor head echo dopplers in the begin. It is usual that the MS head echo doppler radio scatters are very weak but the apparent high sky electric discharges they usually trigger produce a lot stronger radio scatters showing as kind of meteor scatter ‘tails’.

Third pic shows two MS head echo dopplers on Kirov and Moscow TV carrier freqs with immediate EDS tails showing sets of 50 Hz TV side bands.

Please click pics to open them. Receiving aerial for these pics is a 6-over-6 horizontal 6m band yagi pointing east. Receiver is an inexpensive RTL dongle used with SDR-V3 and Spectrum Lab softwares. Time labels on strips are UTC + 2 h Finnish local. Frequency scales are on the top of strips as Hz.

Some meteor scatter head echo dopplers have no ‘tail’. This may be because there happens not to be any high voltage atmospheric electricity to discharge at the point of these meteor high sky strikes. First pic shows MS head echo dopplers without EDS tails.

Most electric discharge scatters (EDS) visible on specrum strils appear to occur without any marks of meteor doppler initiating them. This suggests that either the MS head echo dopplers are too weak to register on receiver strips or the high sky electric discharges are initated spontaneously without help from meteor strikes.

Spectrum strip on second pic has registered three MS head echo dopplers. The longest them is on Moscow TV frequency. Another is on Segezha Nadvoitsy TV. Then there is a weaker one on Moscow TV. These MS hits have very short and weak EDS tails only.

The third screenshot has captured 5 meteor scatter head echo dopplers on Moscow TC frequency. The center one of the dopplers shows stronger than the others. It appears to have initated an EDS ‘tail’ that is strong enough to scatter TV carriers and side bands on wide bandwidth and apparently on many TV transmitters.

Automatic Spectrum Lab periodic screenhots. Two meteor scatter head echo dopplers on Moscow and Kirov TV freqs are initiating immediate ‘tails’ of TV carrier electric discharge scatters and TV 50 Hz side band sets.

From the second pic a sharp observer can find two sets of faint meteor scatter head echo dopplers scattering sets of TV 50 Hz side bands. The following ED scatters are so strong that they almost hide the triggering meteor scatter head echo dopplers.

Third image show a faint meteor scatter head echo doppler initiating EDS on Kirov TV freq and soon after it a stronger MS head echo doppler on Moscow TV freq producing strong and wide enough EDS tail to momentarily raise receiver AGC and put the strip background black.

I started yesterday observing MS head echoes on R1 TV carriers with setup that experienced MS spotter Esko OH2AUP kindly instructed. With new SDR-V3 wide band multi freq setup I could monitor most of the TV carriers simultaneously to observe MS on them. The aerial is a 2 x 6 -el yagi array for 50 MHz. Receiver is an inexpensive RTL dongle. It seems that I am getting most of the MS head echo dopplers from rather distant TV tx carriers like Moscow, Kirov and Syktyvkar TV. Moscow TV together plot MS head echo dopplers about every 2 … 4 minutes. Closer to me St Petersburg and Segezha Nadvoitsy TV tx’s plot only occasionally, just a few MS head echo dopplers a day. Non-doppler spread spectrum ED scatters are so numerous that they were not counted.

The long baseline meteor doppler observation makes sense when thinking that meteor hits occur very high. It is easier for low horizon aimed TV tx aerial lobes to hit high sky objects from long distance than from close where they are high above the directional patterns of their aerials. Also there is more space to collect greater number of meteor hits between on long rx-tx baseline than between close rx and tx.

Further, high ERP radiated power of TV tx of course brings the usually weak MS head echo dopplers visible easier than on low power beacons. The St Petersburg and Moscow R1 ch TV tx’s have very high ERP power. This should make it practical to copy MS head echo dopplers on their carriers in Central Europe, too. Yagis may be needed for receiving real MS head echo dopplers, however. Meteor EDS tails are much stronger so they are of course visible even with low power receiving aerials.

Remote Listening to MS head Echoes

For those who have no access to 6m band MS receiving aerials I am streaming ‘radar voice’ online as ordinary stereo sound. Spectrum Lab is able to copy remote MS head echo dopplers from this stream through one’s internet browser and virtual audio cable.

I will provide ready Spectrum Lab USR configuration files for MS capturing for those who wish to try. ‘Radar voice’ as online steamed stereo sound:

In the future, I have in mind to develope an automatic high sky scatters like MS, Es and ionospheric lightnings locating network of voluntary ham and radio hobbyist receiving home stations. For this, voluntary software developers are needed first. Please let me know if you have coding skills and are interested in joining the effort.

Pics of Strong Meteor Dopplers

On first pic is a MS head echo doppler strong enough to plot dopplers on three freqs. The strongest is on Moscow TV carrier and the two others symmetrically up and down are possible meteor doppler twins on Moscow TV side bands because they are of same shape as the center one.

Next pic features a rather long MS head echo doppler on Moscow TV carrier.

Third image illustrates a long and strong meteor head echo doppler that shows up above at least three TV carrier frequencies: Arkhangelsk/Cherepovets, Kirov and Syktyvkar TV. There appears to be faint fourth doppler above 49748 kHz. These are similarly curved but on different angles so it might be possible to locate this meteor hit by these dopplers.

A couple detail images of meteor scatter (MS) dopplers captured from the online ‘radar voice’. The sound streaming R1 TV channer multistatic radar RTL receiver is now connected to an east pointing 2 x 6 el yagi array. This aerial appears to capture meteor scatter ‘head echo’ dopplers rather well likely because it listens to a large area surrounded by many 6m TV analog transmitters serving as powerful MS beacons.

Small MS dopplers appear every few minutes and fairly long head echo dopplers about a couple times an hour. I have not bothered to count those numerous high sky electric discharge scatters (EDS) occurring every few seconds although some of them are triggered by meteors.

The stereo radar voice contains low R1 band TV carriers starting from 49739 kHz up on left stereo channel and high band R1 TV carriers starting from 49755 kHz up on right stereo channel:

Attached images are cropped screenshots from Spectrum Lab (SL) windows registering MS head echo dopplers from online streaming passive multistatic radar stereo voice. These SL windows are set for 1 pixel/FFT bin and 70 mS/line sweep for about one minute meteor scatter strips.

‘Electric Discharge Scatters’ are very usual radio scatters from natural high sky electrostatic discharges like sprites, elves, thunderstorm Es, aurora etc. High altitude discharges ionized air making it conductive enough to scatter radio waves until they rather soon after discharge ceases, cool down and vanish from our receiver strips. So they work quite like little bits of ionosphere except that they have short life time. Sometimes EDS bursts are triggered by atmosphere hitting meteors and are visible on their radio scatter spectrums as their ‘tails’.

High sky discharges appear to be part of global atmospheric electric discharge circuit from high voltage charged solar wind all the way down to ground below our feet. Common ground striking lightnings seem to be the lowest part of the chain of these atmospheric discharges.

Like the thunderstorms, the global daily rate of these natural high atmosphere discharges appears to be constant. This means they occur all the time, although their densest discharge areas appear to move apparently by daily changes of ionosphere.

Spread Radio Scatter Spectrum

A distinctive mark of EDS is its spread spectrum of noise that it modulates to radio waves scattering through it. The higher the atmospheric electrostatic discharges occur, the wider they seem to modulate radio wave scatter spectrums and the longer their lifetime is.

Highest easily visible sources of spread spectrum radio scatters are the Northern Lights with their very strong and wide ‘aurora scatter’ spread noise spectrum, familiar to us radio hams as the ‘aurora tone’.

Unlike fast meteor scatter head echo dopplers, the ED scatters usually have little or no doppler shift which means that they are mostly stationary. Sometimes they have small doppler shift which appears to be caused by high altitude winds blowing them. Instead of the sharp doppler of MS head echoes the EDS have their characteristic spread noise spectrum.

MS Triggered ED Scatters

Usually but not always a strong ED radio scatter follows after a MS head echo doppler. This suggests that the downshooting meteor ionized tail initiates along itself an electrostatic discharge between high voltage charged ionospheric layers.

This electric discharge through meteor trail makes a lot stronger and longer lasting radio scatter than the original meteor trail. Their difference is that while meteor doppler has a wide linear doppler shift of high velocity, the EDS tail has little or no doppler shift but instead a spread noise spectrum.

Because the ED scatters usually immediately follow meteor scatters they are commonly but incorrectly believed to be meteor scatters. In reality, they seem to be scatters from natural high altitude electric discharges triggered by meteor downstrike ionized tails.

Spontaneous Atmospheric Electricity Discharges

However, majority of ED scatters show no MS head echo so they appear to discharge spontaneously, possibly by solar wind charging voltage exceeding breakthrough limit to lower layer of ionosphere.

The high atmosphere discharges strike step by step down to the lower layers of ionosphere until the accumulated atmospheric charge finally finds its way down to ground, usually by a charge carrying high vertical wind rotation of a thunderstorm cloud. When a thunderbolt strikes ground the atmospheric electricity circuit is closed.

Natural ED scatters are quite like any ionospheric propagation better visible on lower radio frequencies. That is why there are a lot of them on low VHF bands like the 6m band. They can be heard also on HF when the high background interference allows.

As part of the global atmospheric electricity circuit the high sky ED’s create very many effects observable with radio waves. Old hams were correct when calling the background noise audible through their aerials and receivers as ‘static’, meaning natural electrostatic atmospheric noise (QRN).

Some Examples of EDS:

Ordinary Electric Discharge Scatters (EDS):

Electric Discharge Explanation of Nasa ‘Aurora Arrow’ Photo:

Curious Shapes of EDS’s:

Directions of a natural high sky radio scatters?

Strong 6m TV High Sky Scatter Pics - Parts 1-5:


Attached MS Doppler Screenshots

Pic 1: A long meteor scatter (MS) head echo doppler which crosses Moscow TV carrier with abt. 2.5 kHz doppler shift. Visible weaker on St Petersburg and Arkhangelsk/Cherepovets TV carrier freqs, too. The EDS tail appears have ignited before the MS doppler appears. This suggests that this EDS burst may have initiated spontaneusly or by another MS hit and occurs only coincidentally over this unusually long MS doppler.

Pic 2: MS dopplers are usually short and rather rare on St Petersburg TV carrier, maybe either because it is so close and aerial beam is aimed so low that there is not much high meteors that hit between it and rx and low enough. However, here is one that apparently has been large enough to reach down into St Petersburg Tx beam. Strength and length of the MS head echo suggests that it has hit somewhere rather close to SE Finland. The EDS tail of this meteor hit is so strong that it raises TV side bands clearly visible.

Pic 3: A simultaneous MS doppler on St Petersburg and Moscow TV freqs. This one has a very weak EDS tail only.

Pics are cropped from the original set of two Spectrum Lab windows to fit the message thread. Captured from the online radar voice stream from RTL rx with 6-over-6 6m H-yagi array (Y12H) aerial pointing dir 100 degrees. Time labels are Finnish local UTC + 2h. Frequency scale is at top as Hz with usual R1 channel TV Tx’s marked. Please click pics to open and see dopplers.

Meteor scatter (MS) head echo (HE) doppler appears on up to six 6m band R1 ch TV Tx freqs simultaneously. There was aurora which made some of these TV carriers ‘fat’ by the aurora typical electric discharge scatter spread noise spectrum.

Fast strip detail: 2018-03-23-221115 FT - Rec fast 5mS playback FFT 4096 - Remote streaming MS RTL SDRV3 R1 TV - Ant D4H - MS head echo dopplers - Long K S P N 6x © OH7HJ
Slow strip monitor: 2018-03-23-2209 FT - Remote streaming MS RTL SDRV3 R1 TV - Ant D4H - Meteor scatter head echo dopplers - Long K S P N 4x - EDS tail © OH7HJ

On St. Petersburg TV carrier there is a faint fifth MS HE doppler right below the strong one. The weak MS doppler is probably caused by meteor trail crossing of one of the small Lake Ladoga area TV Tx carriers like Kotkozero or Suoyarvi. There are also traces of sixth MS doppler on Nyandoma TV freq.

Concluding dy bistatic radar baseline forward scatter effect on Tx’s the likely directions of these MS doppler crossings a possible meteor hit area might be East Finland or Carelia. Meteor scatters like these on multiple Tx frequencies simultaneously could be tracked and located if there were software available for it.

Known TV Tx’s are listed in the scale on top of of each screenshot. Frequency scale is in Hz. Time stamps are FT local plus online streaming delay of abt 10 … 20 s. Recording playback time stamps are arbitrary. Captured and cropped from the online 6m MS multistatic radar voice stream on:

50 MHz TV-bandin radiopeilauskokeiluja Spectrum Labin RDF-modella. Ekan liitekuvan oikeanpuoleisissa SL-nauhoissa on kummassakin sama Pietarin jakso, mutta eri antenneista, kuunneltuina koherentiksi muokatun hamssivastaanotinparin kautta. Vasemmanpuoleisella nauhalla näkyy näiden kahden antennin vaihesiirto, joka vastaa kutakin väriä. Eli aallon tulosuunta.

Nauhalta näkyy, että RDF antaa suuntiman periaatteessa spektrin jokaiselle pisteelle. Kun hiirellä osoittaa nauhaa, viereiselle ruudulle ilmestyy spektripisteen taajuuden, ajan ja sinkunvoimakkuuden lisäksi sen suuntima asteina. Pietarin, Kotkozeron ja Suojärven lähetinten tunnettuja suuntia voi käyttää suuntimien kalibroimiseen. Tällainen kahden antennin suuntimo antaa tietenkin myös peilisuuntia.

Ensimmäisessä oheiskuvassa lentsikkadopplereiden värit liukuvat suuntiman muuttuessa koneiden lentäessä kuunteluasemani ohi. Lyhytkestoiset luonnonskatterit esiintyvät eri väreissä, niiden aallon saapumissuunnan mukaan. Kolmannen liitekuvan aurorapurskeessa näkyy revontuliskatterin tulosuunnan vaihtelu aurorakohinan värin vaihteluna.

2018-04-03-1450 FT - RDF - St Petersburg D4E - Y6H 330 - Curly HMO © OH7HJ.JPG
RDF St Petersburg D4H - Y6H 330 © OH7HJ - 2018-04-02-2100 - Natural wide scatters from same direction.jpg
RDF St Petersburg D4H - Y6H 330 © OH7HJ - 2018-04-03-0011 - Aurora front RDF directions.jpg

Tästä keskeneräisestäkin koejärjestelystä selvisi, että softa ja vastarien yhdistäminen koherentiksi eli samanvaiheiseksi pariksi näyttävät toimivan. Tämä järjestely ei ole vielä valmis ihan ‘oikeiden’ suuntimien ottamiseen. Tekee vielä liikaa suuntien monikertoja, koska tilapäisantennit ovat keskenään erilaiset, ja liian kaukana toisistaan.

Kunnollisen RDF-antenniparin rakentamista on siis tiedossa, kunhan lumet sallivat. Sitten pitäisi päästä harjoittelemaan TV-lähetinten, meteorien, yläsalamien ym. taivasaaltojen peilausta. Jos pelittää, niin on paljon vaivattomampi ja nopeampi menetelmä suuntia, kuin numeerisesti laskien usean eri noden dopplereista. Toinenkin aseman tietenkin tarvitaan ristisuuntimien ottamista varten.

T: - HJ

Started experimenting with radio direction finding (RDF) of MS head echo dopplers and other high sky scatters, inspired by inexpensive radio interferometry setup introduced by PE1ITR.

Only software that I know is available for us hams with interferometry RDF option is the familiar Spectrum Lab. So I joined a pair of FT100 ham receivers together to create a coherent pair of Rx’s needed for a simple two aerial interferometer.

These first pics show examples of 6m band MS HE’s in different colors. Each color is for phase shift between these two signals for separate aerials. In practise, for direction of wave arrival. Two aerial interferometer of course gives mirror directions, too.

Directions of Meteor Head Echoes

First of these strip shows two MS HE’s of same color on Moscow TV frequency. Maybe fractures of same meteor traveling together? Between them is another of different color from another direction. 2018-04-03-1730 FT - RDF - Moscow D4E - Y12H 100 - MS HE © OH7HJ.JPG

Next strip has a long and a short MS HE propagating from different directions. 2018-04-03-1732 FT - RDF - Moscow D4E - Y12H 100 - MS HE © OH7HJ.JPG

Third pic shows a long MD HE and at right for comparison a slow RDF strip at center and pair of raw stereo SL strips from the rx and aerial pair at right. 2018-04-03-1733 FT - RDF - Moscow D4E - Y12H 100 - Long MS HE © OH7HJ.JPG

Although this experimental arrangement is incomplete by its temporary unpaired aerials that are too far from each other, it seems to confirm that both the SL RDF software and the homebrew coherent rx modification appears to work.

Later when able to build proper RDF pair of aerials - I hope - will be able to provide reliable directions of arrival for natural high sky scatters like these MS and EDS. Still further, will of course need another RDF node for crosslocating these scatters.

Streaming MS voice:

Simple interfereometer explained by PE1ITR: … ometer.htm

73, - Juha OH7HJ

More examples of meteor scatter head echoes (MS HE) on radio direction finding (RDF) Spectrum Lab strips from R1 channel Moscow TV carrier frequency.

Colors represent direction of arrival of each meteor scatter.

Eilissäöiset revontuliheijastukset näkyvät ‘pumpulisina’ kohinajaksoina puoliltaöin ja aamulla tässä tutkanauhalla parhaiten Vienan, Pietarin ja Sekeen TV-lähetinten taajuuksilla. Myös eteläisempi Moskovan TV on näkynyt auroraheijastuksena keskiyön aikaan, mikä yleensä merkitsee revontulirintaman laajentuneen tuohon aikaan pisimmälle etelän suuntaan.

Tunnetut TV-asemat on merkitty kuvan yläreunan asteikolle. Aikaleimat vasemmalla ovat Suomen aikaa. Kuva: 2018-04-10-1157 FT - PK-N RTL SDRV3 SL Y6H 360 - R1 TV wide spectrum - Aurora bursts © OH7HJ

Revontulten vaiheita voi seurata lähes livenä puolen tunnin välein päivittyviltä monipaikkatutkan online-demosivun nauhoilta, joista ylempi näyttää TV-asemien kantoaaltotaajuuksia suurennettuina ‘detaljikuvina’, ja alempi ‘revontulitutkakuva’ leveänä spektrinä:

T: - Juha

Aurora Borealis or Northern Lights are sometimes preceded by radio scatters of something that appear like short aurora flares. These ‘aurora precursors’ appear otherways quite like usual long duration aurora scatter on these passive radar strips except that they last only about a minute.

The high sky events that create these 50 MHz rather short radio scatters are not yet known but by the wide spread noise spectrum of these scatters they appear to be high altitude electric discharge scatters (EDS).

Spectrum spread effect of natural radio scatter is supposed to indicate that there are ions or plasma accelerated by high voltage field. The acceleration probably creates the spread noise spectrum by doppler effect of radio wave scattering from a swarm of accelerated air particles. Here are examples of these short aurora scatter like bursts.

Reading Spectrum Strips:

A fast Spectrum Lab Radio Direction Finding (RDF) strip is at left, revealing the precursor burst structure on quick time scale.

At center is a slow RDF strip plotting the noise bursts of aurora precursors tells that they are occurring randomly every few minutes. Narror curves and lines are aircraft scatter (AS) dopplers that change their RDF color by their bearing as they pass by the receiver.

At right is a pair of ‘traditional’ SL strips showing spectrums from the two aerials used for the RDF experiment. Left strip plots St. Petersburg TV carrier frequancy from an omnidirectional 50 MHz 4-el H-dipole array and right strip from a 6-el H-yagi pointing dir 120.

Aerials are 10 m apart from each other. They are not a matched pair with correct separating distance so this RDF direction scale is not calibrated. However, differences of scatter RDF colors indicate differences in scatters directions of arrival related to Rx. Receivers are two FT100’s coupled together to create a phase locked coherent pair suitable for interferometry RDF experiments.

73, - Juha OH7HJ

In the midnight, after the evening short ‘aurora precursor’ EDS bursts an actual aurora discharge was ignited with its cloud like wide noise spectrum puffs. The direction of the aurora discharge radio scatters appears to change as the aurora flares move on the aurora front (Aurora oval) surrounding poles. When Northern lights discharge front expands it moves farther from North pole bringing the spectacle visible from north further to aurora spotters in the Central and even Southern parts of Scandinavia.

Usually the aurora discharges start from northeast and gradually move to north and further to northwest until they fade out with the sometimes spectacular ‘flashing’ or ‘dancing’ period of rapidly moving aurora discharge flames before they fade out and retreat beyond northern skyline.

The Spectrum Lab Radio Direction Finding (RDF) function indicates the movements of these Aurora Borealis discharge flares by changing colors. Here is a set of slow narrow spectrum RDF strips of igniting and fading os a rather short period of Northern lights discharge.

These aurora scatters were captured on St. Petersburg TV R1 channel carrier frequency with a homebrew pair of phase locked FT100 ham receivers listening to a yet unmatched RDF pair of 50 MHz aerials. Color indicated directions are not calibrated. Narrow curves are aircraft scatter dopplers and straight lines are TV transmitter carriers and side bands, directions of each indicated by SL RDF colors.

Remark: In these screenshots the short noise puffs of ‘aurora precursors’ appear synchronous with bypassing aircraft dopplers. Maybe jet condensation trail scatter? Or something related to electric discharges agitated by high flying aircraft? Or pure coincidence?

73, - Juha

Fast strip radio scatter details of phases of the aurora discharge described in previous report. Captured on St. Petersburg TV R1 carrier frequency.

First set of fast aurora spectrum strips: Igniting fresh aurora discharge is visible as a constant noise spectrum strip left of the three narrow lines of TV carriers. RDF colors indicate directions of each signal. Among are occasional short wide EDS bursts and short sets of TV 50 Hz side bands scattered as narrow MS tails or narrow spectrum EDS.

Second set of strips: The aurora discharce wide noise spectrum appears to live as the aurora scatter noise belt moves or is created on both sides of the TV carrier lines. Third and fourth strips have longer side band scatters. Fifths strip is plotting a long ‘aurora precursor’ burst.

Third set of aurora scatter strips: The aurora discharge gradually fades from its full power shown on the first strip. Second strip shows what seems to be an aurora flare scatter propagating from different direction than from the main aurora discharge front. Third strip has captured an ‘aurora precursor’ burst. Fourth and fifth strips illustrate aurora discharge gradually fading to a narrow noise line at left among natural wide EDS and narrow spectrum 50 Hz TV side band scatters.

73, - Juha

Finnair training flight circling flight route doppler track on St. Petersburg TV carrier frequency. Right Spectrum Lab strip is 200 Hz wide and left strip 100 Hz wide for more details.

A rather low flying aircraft at about half a kilometer altitude and lower at approach is rather well visible on St Petersburg TV carrier. Apparently the low VHF rather long wavelength waves of the powerful TV Tx bend enough down below horizon to illuminate a flight below theoretical radio horizon from the transmitter.

Receiver is a standard cheap RTL dongle listening to a 4-element dipole array aerial and receiving software is a SDR Console V3 streaming 22 kHz wide spectrum of the R1 TV channel to analyzing multi Spectrum Lab windows.

A FR24 playback map illustrates the plane route with training approaches to the EFLP airport.

Meteor scatter (MS) head echo (HE) dopplers on radio direction finding (RDF) spectrum strips at St. Petersburg TV frequency. MS head echo doppler scatters are rather weak so it is reasonable to assume that those MS hits occurring between Rx and Tx near the baseline appear stronger on strips by the forward scatter baseline effect than those away from the Rx-Tx baseline.

Although the St. Petersburg TV has a high power R1 ch transmitter these MS HE dopplers appear less frequently on it than on faraway TV Tx’s like on the high power Moscow TV carrier. Reason may simply be that less meteors hit between shorter distance of Rx and Tx than between long distance Rx and Tx. TV Tx aerial radiation vertical pattern may be directed too low for nearby MS hits which may also partially explain why receiver captures less MS HE dopplers on relatively close TV carriers.

These meteor scatters were captured on St. Petersburg TV carrier frequency with a homebrew pair of phase locked FT100 ham receivers listening to a yet unmatched RDF pair of 50 MHz 4 … 6-el aerials. Color indicated directions are not calibrated. Straight lines are TV transmitter carriers and side bands, directions of each indicated by Spectrum Lab software RDF colors.

Capturing MS HE in Europe?

An ideal distance to capture MS HE dopplers on 49749.975 kHz St Petersburg TV might be something like 1000 km away or even more? In countries like Sweden and Norway and Poland the St Petersburg TV should give MS dopplers with fairly good 50 MHz ham aerials. Usual 4 … 6 element 6m band aerials are adequate for capturing MS HE dopplers.

For Poland and Germany, for instance, 49747.398 kHz Moscow TV might be a good source of MS HE. Still more west in Central Europe like in Belgium and NL, some TV Tx’s in East Europe might be good sources of MS HE dopplers.

For Central European MS doppler spotting, candidates of R1 channel TV Tx’s might be for example 49739.360 kHz Kaliningrad. For those having aerials for the R2 TV channel there are more Tx’s, like 59250.007 kHz Kiev.

Please find more MS suitable TV beacons from Jürgen’s TV list:

73, - Juha

Nyandoma TV carrier frequency provides more meteor scatter head echo dopplers although its Tx is farther away and has lower power than St. Petersburg TV Tx. An possible explanation for more MS HE hits on remote TV Tx is that more meteors hit between longer distance than between short distance Rx and Tx.

There are also more ‘low MS dopplers’ on Nyandoma TV than on St. Petersburg TV freq. Also this may be caused simply by the longer distance higher number of MS hits. A few of the meteors may hit atmosphere in shallow angle away from the Rx-Tx baseline. In such less usual cases, the path of radio scatter reflection (bistatic range) is extended, creating a ‘low doppler’.

The more regular ‘high MS dopplers’ with their MS head edcho (HE) dopplers mostly on the high doppler shift part of TV carrier are common because meteors usually hit from up to down. Downwards meteor hits create a shortening radio scatter path of reflection which shows on strips as a ‘high doppler’. High dopplers are to the right of the center carrier in the example strips attached.

Usually the ionized ‘meteor trail’ visible as stationary line or set of TV side band lines cools down and fades out from the view of scattering radio waves in a few seconds. Sometimes the trail survives for a number of seconds like the one on the third strip from left of the attached set of MS head echoes on RDF strips.