Today I had a talk about Aircraft Scatter with Michael, OE1CMW, who recorded it to produce a podcast for his series “ON AIR – Amateurfunk D-A-CH“. As it´s in german language, I keep this post in german.
Heute habe ich mit Michael, OE1CMW, über Aircraft Scatter gesprochen. Michael hat das Gespräch für seine Podcast-Reihe “ON AIR – Amateurfunk D-A-CH” aufgezeichnet.
In meinem Blog finden sich viele Beispiele zu QSOs und Bakenbeobachtungen als Anregung für eigene Aktivitäten. Unter dem Menü-Punkt “Aircraft Scatter” habe ich die QSO-Prozedur ausführlich beschrieben. Das Programm AirScout von Frank, DL2ALF, gibt es als Download für das Betriebssystem Windows.
Hier als Beispiel ein QSO mit DJ5BV auf 23 cm. Man hört sehr schön die Änderung der Tonhöhe infolge des Doppler-Effekts und verschiedene Signaltöne durch Reflexionen an verschiedenen Flugzeugen.
Wenn man Baken beobachten will, sollte man WideGraph von WSJT-X mitlaufen lassen, dann kann man auch schwächste Signalspuren sichtbar machen und auch die Doppler-Verschiebung sehr gut visualisieren.
IARU officials are working hard to defend restrictions to or, in worst case, the loss of the 23 cm amateur band. Barry, G4SJH, just posted a document about the forthcoming in the certain hearings.
F5ZNI on 13 cm in JN19BQ, 440 km away, is a good indicator for troposheric duting to the west. Drifting up and down, it is transmitting just a little below GPS locked DB0UX in JN48FX, just 105 km to the south.
This is, how it usually looks, when I monitor F5ZNI on about 2320.899 MHz. DB0UX to the right with space 800 Hz lower. F5ZNI about 1250 Hz lower with space 500 Hz up.
Tonight DB0UX appeared a little different, somehow screwing through the waterfall display.
What happened?
Well, there is a windmill in 500 m from my QTH a little north of the path to F5ZNI and the wind raised to blow with 6 km/h from NE ……
Artist conception of the James Webb Space Telescope. (Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez)
As the long-awaited launch of JWST happened recently at Christmas and it is on the 1.5 million km journey to Lagrange Point L2, I found some time to collect information about the communication system. I was very pleased to see a frequency in the satellite band next to the 13 cm amateur radio band. It is being used for a telemetry downlink with 6 W into a pair of omni-directional antennas. Feed and LNA are not really designed for this part of the band, but still usable with some loss. Later the scientific traffic will happen in the 26 GHz Ka-band.
When looking for tracking data, I found a two line element data set at NORAD dating back to December 28, 2021 for JWSTs NORAD number 50463.
My tracking software accepted it and the calculated information looked very plausible, as the distance to the object was very close to the one published on the official JWST website and azimuth and elevation pointed roughly to L2. I am aware, that JWST must not fly on the direct line, as it will be in a wide orbit around.
Five Lagrange points in the Sun-Earth-System (not to scale). (Credit: NASA)
As in the past, when I received signals from exotic sources like ISEE-3 and Longjiang-2, I used my 3 m dish with the ring feed and LNA for 2320 MHz. I tried to use one of my PLUTO SDRs instead of the 13 cm transverter, but these are far too deaf and the LNAs gain of 16 dB is not enough to show any change in the noise, when switching it on and off. So I used a similar configuration, as before and mounted the 13 cm band ATV converter, I used to receive TV signals from the ISS, to get a sufficient signal level on the IF for the PLUTO.
Trace of the JWST signal, it is not audible. (DJ5AR)
Last, but not least, I saw a trace in the waterfall diagram, a little below the operating frequency. I calculated the doppler of the moving probe to about -2 kHz, which has to be combined with the doppler effect resulting of the Earth rotation. I found the signal 1 kHz too low in the reading, but the PLUTO is stabilized just by an OCXO only and the converter is not locked at all, so I didn´t worry about the difference. Turning the dish away and back to JWST resulted in disappearing and reappearing of the signal. The observed doppler drift over 1.5 hours matched quite well the calculated drift caused by Earth rotation. The shift at the rise is about -400mHz and at the set -2900 Hz, -200 Hz per hour.
Well, I am pretty sure, I have received the signal of the James Webb Space Telescope in a distance of nearly one million kilometres!
Artist conception of the James Webb Space Telescope. (Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez)
Nachdem das James Webb Weltraumteleskop (JWST) an Weihnachten gestartet worden und auf dem 1,5 Millionen Kilometer langen Weg zum Lagrange-Punkt L2 ist, habe ich beim Stöbern im Internet Informationen und Frequenzen zum Kommunikationssystem gefunden. Demnach sendet es im dem 13-cm-Amateurfunkband benachbarten Satellitenbereich (S-Band) mit 6 W an einem Paar von Rundstrahlantennen Telemetriedaten zur Erde zurück. Der Erreger in meinem Parabolspiegel und der dort installierte Vorverstärker arbeiten hier (50 MHz tiefer) zwar nicht mehr optimal, aber noch brauchbar. Die spätere wissenschaftliche Datenübertragung wird im Ka-Band bei 26 GHz erfolgen.
Das Wissen um die Sendefrequenz ist die eine Sache, die andere ist, die Antenne auf den richtigen Punkt am Himmel zu richten. Antennennachführung für Satelliten im Erdorbit besorgt bei mir ein kleines Programm, das mit sogenannten „Two Line Element Sets“, die von der amerikanischen NORAD stammen, gefüttert wird. Für das Weltraumteleskop mit der NORAD-Nummer 50463 sieht das letzte verfügbare Set vom 28.12.2021 so aus:
Ich war mir nicht sicher, ob das auch mit Objekten funktioniert, die den Erdorbit verlassen haben, aber der Vergleich der von meinem Programm berechneten Entfernung mit der aktuellen Angabe auf der NASA-Webseite zeigte ähnliche Werte um 920.000 km. Zudem sahen auch die Richtungswinkel plausibel aus und wiesen in etwa zum am Nachthimmel auf der Verbindungslinie Sonne-Erde liegenden Lagrange-Punkt L2. Da das Teleskop in einen weiten Orbit um diesen Punkt eintreten soll, gehe ich davon aus, dass es auch nicht genau auf der Verbindungslinie Erde – L2 fliegt.
Die fünf Lagrange-Punkte im Sonne-Erde-System (unmaßstäblich). (Credit: NASA)
Für den Empfang habe ich, wie schon bei der Kometensonde ISEE-3 und dem Mondsatelliten Longjiang-2, meinen 3-m-Parabolspiegel, Ringfeed und Vorverstärker für 2320 MHz, ATV-Konverter mit LO= 916 MHz und ein ADALM-PLUTO SDR (Software Defined Radio) am Laptop benutzt, um den empfangenen Frequenzbereich in einem Wasserfalldiagramm sichtbar zu machen. DerPLUTO ist in dem Frequenzbereich leider viel zu unempfindlich, um ihn direkt nach dem Vorverstärker (16 dB Gain) einzusetzen. Deshalb dient der Konverter eigentlich nur dazu, das Eingangssignal weiter aufzupeppen und in einen empfindlicheren Bereich umzusetzen. Gleiches wäre vielleicht auch mit einem zweiten LNA mit entsprechender Durchgangsverstärkung zu erreichen.
Spur der JWST-Aussendung im Wasserfalldiagramm. Das Signal ist nicht hörbar. (DJ5AR)
Der langen Rede kurzer Sinn: Wenige Kilohertz unter der Sollfrequenz tauchte in der vergangenen Nacht eine Spur im Diagramm auf, die verschwand, sobald ich die Antenne wegdrehte und wieder auftauchte, wenn sie zurückgedreht wurde und die fortlaufend aktualisierte Position des Teleskops am Himmel weiterverfolgte. Die Frequenzverschiebung nach unten entsteht aufgrund des Dopplereffekts, denn das JWST entfernt sich von der Erde mit hoher Geschwindigkeit (450 m/s). Das wird dazu auch von der Erdrotation überlagert, wegen der wir uns auf der Erdoberfläche in der ersten Nachthälfte dem Objekt etwas “nähern” und in der Zweiten entsprechend “entfernen”. Das mildert die Verschiebung nach unten bis Mitternacht etwas ab und verstärkt sie danach. So liegt die Dopplerverschiebung beim Aufgang bei -400 Hz und beim Untergang bei -2900 Hz. Pro Stunde verschiebt sich die Frequenz um 200 Hz nach unten. Da die Doppler-Verschiebung aber relativ klein bleibt, stellt das kein Problem dar, vielmehr ist sie ein weiteres Indiz, das richtige Objekt im Fokus zu haben!
The QSO BANAT Association organizes FT8 Activity Contests every 1st and 2nd Wednesday each month on 2 m and 70 cm. From 2022 on they added a 23 cm Activity Contest on the 3rd Wednesday. In respect, that FT8 is not useful with propagation modes like aircraft scatter on this band due to the doppler effect, it is open for the use of ISCAT, JT65, JT6m, JT8f, JTMS and MSK144 as well.
After decoding some HA stations in FT8 on 2m and my beacon check found strong signals from DB0AAT and OK0EB on 23 cm as well as from DB0SHF, DB0NCO andOK0EA on 13 cm, I had a closer look at that area. At least I found OE5XHE on 1296.975 in JN78DN24GJ, 1120 m asl. It ist transmitting in A1 with 2 x 3 W into two planar antennas (WIMO) with 9 dBD each. The antennas beam to 105° and 205°. The beacon keeper is Hans, OE5ANL. More information on QRZ.com
OE5XHE to the right on 1296.975 MHz, very weak on 1296.970 MHz a trace of OB0EB and on 1296.965 MHz DB0ANN.
Complainment about the need of having an elevated location and large antennas to become QRV on 23 cm with an IC-9700 inspired me to compare my regular equipment of:
Flex-1500
TV 144 MHz
TV 1296 MHz
LNA 0.35 dB NF
3 m EcoFlex 15
Ringfeed
3 m dish on top of the mast
with my IC-9700, usually in use for 2 m and 70 cm and a minimalistic antenna:
IC-9700
5 m RG213
Ringfeed for 1296 MHz, just on a metal step on the roof
The dish in the upper right and the ringfeed to be seen in the lower left on the metal step, both beaming south. As signal source the beacon HB9BBD/B on 1296.050 MHz has been chosen, 323 km away, on the Rigi Scheidegg in Switzerland, 1670 m above sea level. It is transmitting 10 w into an array of 3 dipoles beaming north.
As the whole air space between Mainz, JN49CV, and Rigi Scheidegg, JN47GA26, is visible, a lot of reflections on airplanes can be expected.
The signal of HB9BBD/B is very strong in Mainz, 40 dB over the noise usually. The gain of the dish is estimated to 28 dBD. The gain of a ringfeed may be 2 dBD and as it has just been layed down on a metal step on my roof, I assume the difference to be more than 30 db.
As expected, the signal could be received with the IC-9700 as well. It is deep in the noise, but increasing, when airplanes cross the path, audible most of the time.
Wide Graph of WSJT-X is a nice tool to display weakest signals and I very often use it to monitor distant beacons. I recommend it to anyone, who want to start beacon monitoring.
Deep in the noise is the signal at the ringfeed and the IC-9700 at about the same time as on the screenshot before. But it is always there and many reflections can be seen, increasing the signal level. Interesting is that different reflections dominate in the two screenshots. That is caused by the different beam widths of the antennas.
The conclusion is, that there is no point of not to try on 23 cm with an IC-9700 and a small antenna. In this example the difference of the receiving systems is assumed to be more than 30 dB. When using a low loss cable, a LNA and a 3 m yagi along with the IC-9700 the difference will be not more than 10 dB, resulting in 20 dB stronger signals.
Aircraft scatter relativizes the disadvantages of locations in valleys and urban areas.
A post by F6HTJ on Facebook informed about the new french beacon F1ZUY on 1296.980 in JN19BQ.
Despite the dish is in the lower parking position at present, I turned it towards France and gave it a little elevation of 4 degrees. Very soon the first refections on airplanes could be seen 300 Hz below the given frequency. The distance to the beacon is 440 km.
The crossing of RYR70SX was strong enought to copy first fragments of the callsign. The beacon is transmitting in A1A with 5 W into a big wheel. Nearly every passenger or freight aircraft, crossing the path, causes reflections.
I am usually happy about every beacon, going on air. As there are many beacons in Europe, the selection of the frequency and its coordination is essential. As many national regualtors grant licenses for a fixed frequency only, a frequency coordination has to be done, before the beacon can go on air. F1ZUY is an example for a beacon that can be heard in a distance of several hundreds of km under normal propagation conditions. Tropospheric ducting can extend the distance to more than 1000 km, probably interfering with other beacons on the same frequency “far” away. So F1ZUY is also a bad example for the lack of coordination by the IARU R1 Beacon Coordinator. It doesn´t matter, whether the keeper didn´t know about the need of beacon coordination or just ignored it. As soon, as LA9SHF will go on air on it´s coordinated frequency of 1296.980 MHz, interference will occur in cases of tropospheric ducting over the North Sea, which happens quite often. Bad luck for beacon observers in Belgium, the Netherlands and Denmark.
So I appeal to all beacon keepers: Please contact the IARU R1 Beacon Coordinator before setting up a beacon or applying for a license!
As there is a lot to do to the house, I could setup my antennas at low level only so far. But despite that, I had some nice QSOs on 2 m in FT8 over the weekend.
I hope to end quarantine next Wednesday to go for a better location on Sunday.
