Empfang des James Webb Weltraumteleskops

6. Januar 2022

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:

1 50463U 21130A   21362.00000000  .00000000  00000-0  00000-0 0  9999
2 50463   4.6198  89.0659 9884983 192.3200  17.4027  0.01958082    27

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!

New Activity Contest for digital modes on 23 cm

December 21st, 2021

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.

OE5XHE: Hrd Beacon #72 on 23 cm

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.

23 cm Beacon monitoring: IC-9700 with minimalistic antenna

2021-11-18

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.

F1ZUY: Hrd Beacon #71 on 23 cm

November 8th, 2021

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!

And back again in Ireland…

May 31st, 2021

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.

Nice Opening tonight

November 29th, 2020

As predicted in the Hepburn forecast, there happened an opening to the west tonight. No really breathtaking distances, but at least three new squares on 2 m (two of them I already worked on 23 cm 😉 ) IN86, IN87 and IN89.

On 23 cm I tried with Grant, G1SDX in IO80FL, first in FT8, but I could only copy him via aircraft scatter due to significant doppler, inhibiting decoding of his signals. He copied me via tropo up to -11 dB, but we had a difference in power of 13 dB (36 element yagi and 10 W vs. 3 m dish and 200 W). So we tried MSK144, where I could decode him via AS, but he had no decodes of me.

It´s a very interesting path, as half of it is over water. It should be an opportunity for combined sea ducting and aircraft scatter. I hope for a chance to try.

Activity as EI8HH is over now

October 21st, 2020

QSOs in October 2020: MS in red, FT8 in green and SSB in blue

While refurbishing our irish home, I found some time in the mornings and the evenings to be active on 2 m. At least I worked 31 squares. Even on 23 cm I got 3 Calls to the log. The rig so far is an IC-9700 with a 7 element yagi and a linear amplifier with 200 W on 2 m and a 69 element yagi on 23 cm,

Now I have to close the station and take the antennas down. It has been a lot of fun and I hopefully will be back next year, if pandemic allows. Many ideas are in my mind now, how to improve the station over here.

Many thanks to Joe, EI3IX, his N adapter female-female allowed me, to run 2 m and 23 cm simultaneously 😉 .

EI8HH on Air

October 2nd, 2020

As some work at our families house in Ireland has to be done, I am spending 3 weeks over here in IO53HN. I got my new IC-9700 with me and have antennas for 2 m and 23 cm. As I have to restrict my movements by government order, no portable activites are possible in the first two weeks. So I will try to work in the UHF/SHF Contest on 23 cm from the southern lake shore of Lough Mask. My favourite direction is to GI/GM. Maybe I can go to a better QTH later in the 23 cm UKAC. On 144 MHz I will focus on meteor scatter in the morning hours.

In a first test on 2 m I worked GI and GM in FT8. GM7PKT came back on my very first CQ. Later I tried meteor scatter with my german neighbour Mathias, DH4FAJ. As he has massive QRM, he couldn´t hear anything, but I copied him twice with +4 dB. So better to try in the morning again.

IC-9700: Drift on 23 cm

September 25th, 2020

A question in a Facebook group about a GPDSO for an IC-9700 to be used on 23 cm for FT8 inspired me for a quick test. As I use my IC-9700 for 2 m and 70 cm only from home, I connected a dummy load to the 23 cm antenna socket. Next was to tune it to 1,296.174 MHz (of course) and to call in FT8.

The result in brief: No problem to decode with my regular 23 cm rig (OCXO controlled). Just a moderate drift and the signal appeared about 100 Hz too low. Nothing to worry about.

But never the less, I prefer JT9f on 23 cm, as FT8 is useless on aircraft scatter.