Satellite Scatter

(2009-02-10) PE1ITR
ISS Scatter

The picture above shows the reception on 143.050MHz of a the Graves Radar signal bounced back from the International Space Station (ISS) during a complete pass. The doppler spans about 12KHz. It is possible to make a two way cw contact on vhf using the iss as a reflector. Needed is a good vhf dx station with automatic satellite tracking antenna. Because of the big frequency drift a automatic doppler correction is also needed.

Doppler Correction
This is a recording of a reflection on the ISS from the Graves radar. An automatic doppler correction of the receiver frequency is used in the recording. To determine the receiving frequency the range rate (RR) must be calculated between the Graves Radar and the ISS and also between the ISS and the observer station. By adding the to RR's the frequency is calculated. Then the computer sets the receiver using a serial CAT interface. The program Predict running in server mode is used to calculate the two RR's from the orbital elements. A seperate program I wrote in Perl extract the information from Predict and sets the tranceiver. The picture below shows the setup.

When making a sked its important to agree on a receive and transmit sequence. Station east-side transmit on 1st minute and Station west-side transmits on 2nd minute. Second point is the doppler correction You can agree that each station keeps the sked frequency contant at the ISS. This way each station does its own doppler correction on rx and tx. Its is also possible that one station does the complete doppler correction. This way one station does al the work and the other station can relax and listens to one fixed qrg.

My First Satellite Reflection Experiment (2007)
On 2007-12-07 I had a sked with DK3WN to try on the ISS. My station was 200W output and 2 x 10 element yagi. DK3WN was using a 10 el crossed yagi antenna. We used cw with 1 minute sequence on rx and tx. DK3WN received my reflection briefly when the ISS was about 50 degrees elevation on my location.
The picture below shows my signal received by DK3WN.

This is the audio recording of that event.

Easy FM mode
If the reflection method is to complicated its also possible to contact the astronauts on the ISS directly. Maybe they want to qsp your message. This recording is an example of this method.