After installation of new transverters for 23 and 13 cm with stabilized LOs a couple of months ago. I gathered some experience in using JT65C mode on EME. So I undertook a new attempt to receive and decode G8MBU via aircraft scatter today. As antenna I use a 3 m dish with a dual band ringfeed.
Path DJ5AR to G8MBU
The beacon is located at Cowes on the Isle of Wight, IO91IR37, 683 km from Mainz, JN49CV. It runs 2 W power into an omnidirectional dual alford slot antenna. The mode used is JT65c. Nominal frequency is 1296.800 MHz. To successfully decode the signal, the SSB dial should be set to 1296.7986 MHz, to get a tuning tone of 1400 Hz in WSJT.
There is a small window between the Isle of Wight and Mainz, where high flying aircraft can be “seen” from either places. But only a few airplanes cross the path within and fewer fly along the path. Reflections of G8MBU could be seen from time to time, but mostly too weak and too short to provide decodes. It took nearly 3 hours until the first decode happened at -22 dB and just some minutes later a second one appeared on the display at -21 dB:
Sometimes you hear words that hurt. Especially if they are true: Some years ago I tried 13 cm EME with Dan, HB9Q, and couldn´t copy anything of him. His comment after the test: “There is no way, not to hear me!” This is frustrating.
So I forgot Moon Bounce on this band and had fun with other activities, mainly on 23 cm. But the over 30 year old equipment caused more and more problems. So I started collecting parts and modules for a new transverter system covering 23 and 13 cm. It had been finished for the last VHF/UHF/SHF contest in March and was tested with good results. In the end of March I tried EME again after 2 years of absence. On 23 cm it worked fairly, but on 13 cm the drift was a serious problem. In a test with Alex, ZS6EME, I could decode his strong Signal, but not vice versa. So I added 10 MHz Double Oven Controlled Oscillators as references to stabilize the transverters.
PY2BS in WSJT-X Wide Graph
Today I tried with Bruce, PY2BS, and heard him strong in the speaker during his prior test with Toshio, JA6AHB: 1131 -6 2.5 2305 #* JA6AHB PY2BS GG66
At this time his elevation was -1.7° and the moon still under the horizon. After the moon set in Japan, we started:
As he switched his RX from 2304.070 MHz to my TX frequency 2320.070 MHz at about 12:14, we completed very fast. I am very pleased now with my first initial on 13 cm, a new grid square, a new ODX, a new DXCC and a new continent! After setting up a new Initials List for 2320 MHz and writing this blog entry, I enjoy my “Radio Operators High”!
Today PI9CAM´s QSL for the first Satellite Bounce QSO via an unmanned spacecraft done by radio amateurs arrived by mail. As we know, there have been previous commercial attempts for Satellite Bounce in the early 60s using ECHO 1 and ECHO 2 which were inflated balloons with diameters of 30 and 41 m. The initial orbits were at heights of 1500 km and 1200 km.
The theoretical radar cross section (RCS) of ECHO 1 was 700 m², but measurements by military radar stations resulted in 900 to 1000 m² in the beginning. Later, the satellite deformed and shrunk. OKEAN-O, the one we used, has a radar cross section of 18 to 20 m² but is in a much lower orbit at a height of 650 km. This leads to quite similar unit power budgets, regardless the difference in size,
Enjoy the movie “The Big Bounce” about our predecessors 55 years ago!
While ISS Bounce took Jan, PA3FXB, and me 2 months of testing and improving to succeed, Satellite Bounce was a much bigger challenge. Despite the fact, Jan and the team of PI9CAM are operating the 25 m dish of the Dwingeloo radio telescope, it took us nearly 2 years, enormous patience and scores of tests until we finally managed to receive “Rs” to complete a QSO today (December 8th, 2015). As far as we know, it is the first time ever, a two way amateur radio contact could be completed by using an unmanned spacecraft as a reflector.Above screenshot shows the position of the satellite at the end of the QSO. The Satellite rose in SSE and set in NNW. A calculative common window opened at the point, marked “O”. Local obstructions were not considered. Due to safety reasons transmissions in Dwingeloo are limited to elevations above 10°. So the AOS (acquisition of signal) happend shortly before the groundtrack of the Satellite crossed the 40th degree of latitude northwards, as soon as PI9CAM started transmissions. Sum of slant ranges (distance between ground station and satellite) was 3400 km at the beginning and 2000 km at the end of the contact.
Much of the reflections remained below the noise floor, but this one of PI9CAM, right at the beginning (14:10:10 UTC), is a nice example, of what can be received:
And vice versa DJ5AR as to be heard in Dwingeloo (14:11:00 UTC):
The used object OKEAN-O (NORAD #25860) is a joint Russian-Ukrainian Earth observation satellite, launched on July 17th, 1999 by an Ukrainian Zenit-2 carrier rocket. The satellite is in a polar orbit of about 650 km height with an inclination of 98°. The mass is 6.2 tons and the RCS (radar cross section) is figured between18 and 20 m². It has been used for research of natural resources, ecological monitoring and hazards prevention. Designed for a life time of 3 years, it is out of service now.
QSO in WSJT-X
In use by the ground stations were the 25 m radio telescope in Dwingeloo by PI9CAM with 120 W and a 3 m dish with 150 W at the feed by DJ5AR in Mainz. The mode used was digital JT9H that comes with the new WSJT-X software by Joe Taylor, K1JT. The transmit/receive periods were set to 10 seconds, working around a center frequency of 1296.300 MHz. The automated Doppler tracking (+/- 60 kHz) has been performed for the complete path on DJ5AR´s side with a homebrew tracking software. The calculative power budget during the QSO was about -154 dBm. This value is very optimistic, as it presumes the optimum reflectivity of the satellite, which depends on its orientation.
Conclusion: The main difficulties in this game are:
Selection of suitable satellites, depending on radar cross sections and slant ranges.
Compensation of the Doppler shift with a maximum rate of 600 Hz/second.
Following Jan´s (PA3FXB) suggestion, we tried the new experimental WSJT-X software. The mode, we chose was JT9 H. Also we agreed in trying full doppler compensation to be used on my side. Everything worked fine, as can be seen in the screenshot below.
Back from our holidays Jan, PA3FXB, and I had another test via ISS Bounce on 23 cm today. As I located a bug in my Doppler correction software, causing unwanted steps, it could be fixed by finding a workaround for the malfunction in compilers NOW() routine, for returning the correct time in milliseconds. So the improved Doppler correction is working smoothly as can be seen and heard in the signals received.
PA3FXB in JTMS received by DJ5AR via ISS Bounce. Center frequency was 1296.300 MHz.
We even had some kind of conversation at the end 😉
As further tests showed, the full doppler correction on my side is working very well now. This enables potential sked partners to work on a fixed frequency by just tracking the International Space Station with the antenna.
Sked requests are welcome: dj5ar (at) darc.de
Modes, successfully being used so far: CW, SSB, ISCAT, JTMS
On April 7th the PI9CAM team hosted some students, working on a film project. So there was some spare time to schedule more tests in our space debris project. The objects, selected to try on, were some rocket bodies. Many of the larger objects in low earth orbits are of this type. The operation style, as usual, was a center frequency of 1,296.300 MHz, 15 seconds periods with DJ5AR transmitting first. This time we wanted to try FSK441 mode, to compare it with the experiences, we had with ISCAT-B.
On two objects, NORAD #39679 (SL-4 R/B) and #39771 (H-2A R/B) we registered faint but continuous reflections. Only partial decodes were possible. It seems, that ISCAT-B is the better choice.
Reflections of DJ5AR in FSK441 recorded at PI9CAM
On SL-4, a russian rocket body, lauched on April 16th, 2014, a modulation of the reflections with a period of 2.8 seconds could be observed. It looks like, as the object is tumbling.
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.
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.
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.