Category Archives: Propagation

A new Goal: Rocket Bodies and other Space Debris

February 22nd, 2015

Since QSOs via ISS Bounce are quite easy to perform, Jan, PA3FXB, and I evaluated the possibilities, to use other objects in orbits around the Earth. The table below shows a selection of objects in earth orbits. There are some quite big ones in geostationary orbits, but the distance is the most limiting factor, not the size, as can be seen in the predicted maximum reception level provided by the radar equation. So I had an intense survey on the objects in low orbits and determined the maximum linkbudgets, to filter the most promising ones. My PC had to work a couple of hours to perform that. On the end it has been a little surprise, that COSMOS 1823, an old soviet geodetic satellite, wasn´t among them. We used it for previous tests and were able to detect faint reflections.

At our meeting on the Dorsten GHz Convention last Saturday, we discussed latest details. On Sunday, Jan and the crew of PI9CAM activated the Dwingeloo Telescope for the 23 cm EME SSB contest, but they had some spare time for other experiments. Just to warm up we had a nice SSB QSO via the moon first, right after their first QSO PA/JW: Congratulations!

H-2A (39771)

Some of the top objects would pass on suitable elevations and we decided to start with NORAD 39771 which is the second stage of a japanese H2A202 rocket, launched on May, 24th 2014 with a radar cross section of 20.7 m². DJ5AR was to transmit CW continously, while PI9CAM checked for reflections. After some trouble with the tracking they caught it shortly before set.

The used power at DJ5AR was 150 W into a 3 m dish (28 dBi) and the PI9CAM team used their 25 m dish (48 dBi) for reception.

The predicted signal level was about -158 dBm, but, as can be heard, it´s clearly audible.

Titan 4B (26474)

Next one on the list was NORAD 26474, the 2nd stage of an american Titan 4B rocket, launched on August 17th, 2000. With a radar cross section of 15.4 m² it is a little smaller than H-2B. But the predicted reception level for Dwingeloo looked very promising anyway:

My signal could be picked up by PI9CAM when the rocket body rised up to 5 degrees over the horizon and they tracked it for about 4 minutes until I lost the object near the culmination point, when the angle velocity became too fast for my tracking system.

2015-02-23 20_21_19-U__Amateurfunk_ISS_Sat-Test 2015-02-22_26474_2015-02-23 20_19_41-U__Amateurfunk_

DJ5AR as received by PI9CAM. Picture is upside down for better matching to the table.

The signal has been detected at an predicted signal level of -160 dBm and became clearly audible soon for serveral minutes. So we can think of trying a CW QSO next time. The drift, which can be seen, has it´s cause in my transmitter, running for the duration of the whole pass without any pause. I will try to reduce the growing spread of the signal by using shorter intervals in the doppler correction.

Marten, PA3EKM, documented this (historical) moment on video:

Many thanks to the team of PI9CAM / CAMRAS:
Cor, PE0SHF,
Eene, PA3CEG,
Marten, PA3EKM,
Gert-Jan, PE1GJV,
and Jan, PA3FXB

Brendan Quest: Could it have been ISS Bounce?

February 21st, 2015

After giving a lecture about “Reflections on Air- and Spacecrafts” at the Dorsten GHz-Convention today, Alexander, DL8AAU, told me, he had discussed the possibility of ISS Bounce with Jeff, WA1HCO, when John, G4SWX, claimed to have received a burst of VC1T on 2 m across the atlantic ocean. Then he asked me about my opinion. Without knowing details, all I could answer was, that the inclination allows the ISS to cross at the latitudes of the stations and that it´s very likely, the stations will be inside the sight range of the ISS then.

First thing I did, when arriving back home in Mainz, was to retrieve an archived TLE file from 2014-07-06. The attempt to calculate a window between VC1T in GN37OS and G4SWX in JO02RF resulted in a direct hit, as the reception of the burst is claimed for 13:41:30 UTC on July 6th, 2014:

As the the above graphs show, a short window of about 1:40 minutes for ISS Bounce opened at exactly the time, John claimed the reception of VC1T. And in fact this has been discussed in the WSJT Meteor Scatter Weak Signal Group as well.

The team members of VC1T and John, G4SWX, as well as those, involved in the discussion in Dorsten were informed to have the opportunity to check out my results. At least there is no doubt, there has been a matching window, exactly in these approximately 10 seconds, John received VC1T.

The TLEs used for this calculation have an epoch date very close to the event:

1 25544U 98067A 14187.56731944 .00009245 00000-0 16720-3 0 9999
2 25544 051.6477 003.4946 0003495 212.8213 225.8239 15.50435882894337

Assumed power and antenna gain for VC1T have been 750 W and, as claimed on their website, 26 dBi. As I didn´t knew much about John´s rig, I assumed 20 dBi as antenna gain on his side. Differences can easily be added or subtracted to or of the above results. Also it hasn´t been considered that the ISS was not in the centers of the main lobes of the antennas. The radar cross section (RCS) of the ISS had been set to 348 m², as was given in the NORAD catalogue, as long as they provided this value there.

For the prediction of the signal level the value of the RCS is essential, as it depends on the frequency, the angle, the reflecing object is seen from the groundstations, the shape of the object, resonances, and eventually by effects resulting of the geometry of the object, as can be seen on corner reflectors. So it´s value should be handled with extreme much care. I don´t really know, whether the value of 348 m² (25.4 dBm²), I used, has been too small or too large. Both is possible.

At present Alexander, DL8AAU, is performing calculations on a digital model of the ISS using a special ray tracing software to get high quality values of RCS. This has to be done under consideration of the orientation and the heading of the ISS, as well as the angles, the ground stations have been seen by the International Space Station.

Path VC1T – G4SWX and Groundtrack of ISS

It is interesting to have a look on the relation of the direct path bethween VC1T and G4SWX in blue versus the Groundtrack of the ISS in red with the window marked green. The bearing of the VC1T antenna has been 62°, while the ISS passed the window under 68°. Vice versa the bearings at G4SWX have been directly 285° and 278° to the ISS.

The main questions are now:

How good is the quality of the assumed value of the RCS?, Can it be improved?
Could this constellation lead to a receivable signal level at G4SWX?

It has to be respected, that John, G4SWX, is a highly skilled operator with more than 30 years experience in 2 m EME and long distance MS over more than 3.000 km. Other propagation modes like meteor scatter, sporadic E or tropo, pure or in combination, are to be considered. There still is the possibility, that the match in time it is just a coincidence.

Joe Taylor, K1JT, has been involved in the above mentioned discussion and he stated there:

“I should make it clear that I have no horse in this race. Like others
who have contributed here, I’m just a bystander with an interest in
knowing the truth about a reported phenomenon.”

This is exactly my point of view in this subject and it is up to the IRTS committee to recognize this contribution.

ISS Bounce or not, we have to respect, it has been a great achievement to cross the Atlantic Ocean on 2m! Applause!

When searching the web for more information, it seems, some had uncertain receptions just with fragments of a decode, finding it not worth to publish it. We are very interested in such “maybe” reception reports, to crosscheck it with a possible ISS window.

If you have any kind of information for us, please forward the exact time and your locator to dj5ar [at] darc.de

In this context it is interesting to know, that in 2007 Peter, SM2CEW and Petros, SV3AAF were very close to complete a QSO via ISS Bounce over a distance of 3136 km in CW!

Opening February, 10th and 11th 2015

February 12th, 2015

The first remarkable opening for quite a long time happened from 10th to 11th of February 2015. F5LENs refractive index forecast promised good conditions for these days. It started with some stations from G, appearing on 2 m. While the activity contests were going on in Scandinavia and the UK on 70 cm, a few operators dropped into the microwave chat. At least two new DXCCs could be worked before going to bed: Steward, GM4AFF in IO86TS and Gordon, GI6ATZ in IO74AJ as no. 30 and no. 31 on 23 cm. Only a few beacons could be heard via tropo: GB3FM in IO91OF, GB3MHZ in JO02PB, PI7ALK in JO22IP, OZ5SHF in JO45VX and OZ1UHF in JO57GH as a new one.

Green: Stations worked on 23 cm Red: Beacons heard on 23 cm

In the morning the inversion had moved to the north-east and never before heard beacons from Sweden became audible on 23 cm. SK6UHI in JO57TX, SK6MHI in JO57TQ, SK6UHI in JO97CJ and SK4BX in JO79LI over 1138 km as my new beacon ODX appeared on the band. Many of the Swedish stations were as loud here as locals. Some of them could be worked on 13 cm as well.

AirScout: New Version 1.1.0.0 is online!

February 10th, 2015

A brand new version of AirScout can be download. Frank, DL2ALF, has implemented a new source for airplane data as well as a couple of new features.

Most spectacular is the ability to track airplanes with the antenna in azimuth and elevation. When enabling tracking, the user can select between several interfaces. I am using the plain WSJT-compatible “azel.dat” file. First tests on DB0NCO are very promising.

AirScout out of Order

January 22nd, 2015

AirScout is not operable at present, due to changes at the data source. Frank, DL2ALF, is active to solve the problem. No planes will currently be shown in the map. If any news available, I will post it here and in the Microwave DX Group on Facebook.

Presentation “Reflections on Air- and Spacecrafts”

January 15th, 2015On February 21st, 2015 Jan, PA3FXB, and I will give a lecture in Dorsten at the GHz convention. It will be held in german and partly in english and is basing on the former lectures “Let´s Bounce”.

We will talk about unusual use of Aircraft Scatter and our experiences using ISCAT. Two years ago the idea, to try ISS Bounce, was born and discussed in Dorsten. We will show what we have done in the meantime in practising this propagation mode.

A big Dish, a big Bird and a big Signal

January 6th, 2015

Jan, PA3FXB, and I skeduled a very special ISCAT test on 23 cm for today. The CAMRAS team had planned to operate PI9CAM with the 25 m radiotelescope in Dwingeloo for some astronomical experiments this afternoon. Before starting with that, we used an ISS pass with low elevation to try ISS bounce with the big dish. Such a pass ensures slow variation of azimuth end elevation angles, which is essential to track moving object like the ISS (or other spacecrafts in low orbits) with an antenna of a weight of 120 tons.

We had very strong reflections right from the beginning, but no decodes. Maybe the signal level was to high? This has to be investigated. Then we changed to aircraft scatter, although the dish had to be kept elevated at 10° by safety reasons, I got strong reflections from airplanes quite close to PI9CAM. Not as strong as from the ISS, but decodable now and it was possible to work in CW too.

Despite the fact, we had no QSO via ISS bounce, we learnt, that it is possible to track objects in low orbits with the 25 m radiotelescope, as long as the elevation keeps low. This opens up a perspective to make use of other spacecrafts as reflectors.

ISS Bounce again: now in ISCAT

January 4th, 2015

Jan, PA3FXB, and I were discussing the use of digimodes on ISS bounce for quite a while. Today we tried it with ISCAT-B and were successful with the first shot. As in the tests with Ronald, ON7FLY, on AS, we used 15 seconds periods.

From the moment on, traces could be seen in the waterfall diagram, decodes were possible.

When the ISS culmiated and the variation of the dopplershift was fastest, the frequency correction came to its limits. But while I am used to ISCAT in the meantime, I needed no decodes to hear, that Jan was transmitting RRRRs.

At least I decoded a 73 from him. The experiences with ISCAT in ISS bounce are very promising, although the 15 seconds periods are too long. So we have to discuss it and try with shorter ones.

ISCAT – a new experience

January 3rd, 2015

Inspired by an article, published by Rex, VK7MO, and David, VK3HZ, in the latest DUBUS [1], Ronald, ON7FLY, and I performed a first test in using ISCAT-B mode (by K1JT) for aircraft scatter on 23 cm. When looking on AirScout it doesn´t seem to be very challenging to have an QSO. But Ronald is obstructed by a hill in eastern directions and he didn´t expect to have an opportunity to work eastwards on 23 cm at all.

Ronald is located in JO10LT and the distance is just 388 km. He uses a 44 element yagi with only 2 W at the feedpoint. On my side a 3 m dish and 150 W are in use. First of all we tried in SSB and were able to complete a QSO after a while. I could copy ON7FLY very weak, but readable. Then we tried in ISCAT-B with 30 seconds periods and it was amazing to see, that Ronald´s signal could be decoded even when only traces appeared in the spectrum.

His signal can be seen in the center section (The drop outs are reactions of the AGC on radar noise). The above sequence could be decoded to:

Since the periods of 30 seconds were far too long, we needed certain airplanes to complete. then we tried FSK441 with no decodes and switched to JT6M and completed the third QSO. In the meantime I found a hint in the above mentioned article, how to reduce the T/R periods to 15 seconds. So we completed a fourth QSO in ISCAT-B again in shortest time:

[1] Rex Moncur, VK7MO, David Smith, VK3HZ, Aircraft Scatter on 10 and 24 GHz using ISCAT: DUBUS Vol. 43 4/2014

Chaos on 1296.942 MHz!

November 28th, 2014

There are good tropo conditions to the east from here for quite a while. I worked OK1MAC on November, 26th with an outstanding signal. OK0EA, SR6LHZ can be monitored constantly. I missed OK0EL on 1296.940, but solved the miracle today. The frequency shifted to .942 and the signal has been covered by DB0AJA. It´s nice to listen, how OK0EL in 526 km distance is battling against nearby DB0AJA,131 km away. As can be seen, DB0AJAs signal is accompanied by several dopplershifted reflections on airplanes.

It is interesting to see, that F5LENs refractive index as well as Hepburns tropo index don´t really illustrate the real conditions today. The conclusions is: Always perform a beacon check before switching off! The result may be surprising.