Category Archives: ISS

ISS bounce III

April 30th, 2013

The doppler shift was the problem to be solved for performing further steps in ISS bounce. There are two practical strategies: If every station will compensate its own doppler component, so even random QSOs would be possible. The other solution is, when the whole compensation will be done by one of the stations. That would open ISS bounce to stations that are able to do antenna tracking on the ISS, but not to compensate the doppler. In this case it is required to arrange skeds, because the compensating station is required to know the coordinates of the other one.

Basing on DC9ZPs E-Book I extended the software, I use for station control, by satellite tracking. That opens the possibility to calculate the relative speed and the resulting doppler shift of the ISS pertaining to given locations and given frequencies.

DJ5AR-EI8HH Elevation DJ5AR-EI8HH DopplerAbove diagrams show the elevation with the according doppler components on 1296 MHz for a window between DJ5AR, JN49CV in Mainz (green) and EI8HH, IO53HN near Galway (blue). If the full doppler compensation will be done by one of the stations, the red line with a total span of 120 kHz will be relevant. The window in this example would open for about five to six minutes.

ISS bounce II

April 8th, 2013

Another test tonight with the experience of the one two days ago, was more efficient in finding the reflections. The ISS passed south of our QTHs. So I could track the whole pass from rise to set. Jan´s signal could be detected most of the time during his window. The picture shows his signal shortly after the rise of the ISS. Caused by the doppler effect it moves from right to left. The shift in this detail varied between 47 kHz and 38 kHz, while PA3FXB was transmitting on 1296.300 MHz in CW.  By a length of about 25 seconds there was a variation of 400 to 500 Hz per second.

PA3FXB shortly after rise without QRG tracking

PA3FXB 2013-04-08 shortly after rise Audio

PA3FXB shortly after rise

PA3FXB shortly after rise with manual QRG tracking

Jan was transmitting his callsign “PA3FXB” followed by “T”s. The variation of the pitch in the first audio file is caused by manually tracking the signal. The second audio file gives an impression of the speed of the doppler variation. An effective  compensation of the doppler effect seems to be most important.

There have been earlier attempts to realize QSOs by reflections on the ISS. SM2CEW reports about nearly completing QSOs on 144 MHz with SM7WSJ in 2007 and he tried also with SV3AAF (more). DF2ZC claims the first ever QSO via ISS scatter on 2 m with DH7FB on December 9, 2007. They completed three more QSOs in 2008. It seems that these were the only four QSOs via ISS bounce since then. VA7MM reports about tests on ISS bounce with VE7BBG on 23 cm in 2004. PE1ITR tried with DK3WN in 2007.

ISS bounce

April 7th, 2013

Tonight Jan, PA3FXB and I tried, what we were discussing about for quite a while. There was a prediction of an ISS pass shortly after local midnight and both of us had no other appointments. So we agreed that Jan should make a transmission on 1296.300 MHz as soon the ISS became visible to him and tracking it as long as possible. My part was to monitor the pass of the International Space Station on my SDR. We used 3 m dishes on both ends and Jan had approximately 375 W in CW.

PA3FXB via ISS Beginning

PA3FXBs signal at the very right

Here is the result. Jan appeared with a relatively strong signal (on the very right), faded out and came back with weaker signal strength. I interpret it, that the first appearance was backscatter and the second was forward scatter, what has to be discussed. Doppler was extremely strong and more than 40 kHZ at the beginning.

Aircraft Scatter, AirScout and the ISS

February 23rd, 2013

Frank, DL2ALF has written an amazing tool for aircraft scatter prediction, called AirScout. Positions of planes are shown in a map like at or, but in addition the path and the part of it, where planes could be seen from both stations will be marked. Frank is using open street map for the maps and an elevation model of NOAA to respect the topography of the path. I made use of a beta version last Tuesday in the NAC on 23 cm and found it extremly helpful.

The latest version can be found here.

Thank you Frank!


Path DJ5AR – IK3HHG with planes and topography

As can be seen in the screenshot, the effective area is excentric to the center of the path. It is displaced southwards because IK3HHGs horizon is limited by the alps.


Eight times IK3HHG shifted by doppler, corresponding to the screenshot above

Last saturday at the GHz meeting in Dorsten Frank told me, that he integrated the groundtrack of the International Space Station to be drawn in the map too. So we have been discussing about the possibility of performing QSOs via reflections at the ISS.


AirScout with groundtrack of ISS

Back home I was very optimistic and used overflights, where the ISS  passed by nort of my location to look out for reflections of GB3MHL on 23 cm, but had no success. There was no trace at all in the waterfall diagram of my SDR. The duration of a pass is only up to 9 minutes and the expected doppler shift is +/- 84 kHz due to the high speed of 28000 km/h. So even if something could be heared or seen, tracking and decoding the signal will be another problem to be resolved.

But anyway: I am looking for somebody to perform tests with me, just to detect reflections at the ISS. Skeds are welcome via chat (ON4KST and HB9Q) or email dj5ar (at)