Recently happysat, a reader of RTL-SDR.com wrote in to let us know about an unusual hobby he has found with the RTL-SDR. Happysat has been using the RTL-SDR together with a QFH antenna to detect old decommissioned satellites in the 136-138 MHz and 150-400 MHz frequency ranges. Although these satellite’s batteries have long been expired, because of some sort of chemical reaction due to thousands of failed recharge cycles the batteries begin to conduct over time and allow the satellite to be powered directly from the solar panels thus activating the transmitter. Happysat writes:

During weathersat reception of NOAA/Meteor on the 137 MHz band i did see quite often unidentified interrupting signals. After a bit of Googling around I learned that these were Dead Satellite’s that still are broadcasting given the right sunlight conditions, the signal strength is sufficient to show up in SDRSharp, not all signals are very strong some very weak and needed a good close up zoom in SDRSharp. There are many shutdown Satellite’s who apparently having a life of their own varying from Military, Navigation, Experimental, Weather, and also Amateur ones. Most are not transmitting any usable telemetry or weather images but they still use the original frequencies to sent out a unmodulated carrier, which interferes with the current operational Satellite’s in the 136/138 MHz band. Normally when a satellite goes out of service and runs almost out of fuel the last reserve is used to shift it in a graveyard orbit which resides above the normal operation orbit, it will be switched off and left on their own. But this will not always goes as planned, sometimes due solar radiation or other technical failures it will not respond again to the ground station commands, which leaves the Satellite in its current orbit. Some have a timer onboard which will be activated at end of life scheduled to end/shortcut the power feed to the transmitter so it will not broadcast again, also this can fail. Until some day they might not work at all anymore.. But that can take a while one of the oldest satellite still broadcasting are: Transit 5B-5 (Military Navigation) from 1964 – they can be heard in either CW or USB mode. An audio example of Transit is over here [link to example] (my recording – link to online stream uploaded by commenter Jordan here) it sounds like some kind of melody song. And LES-1 from 1965 (Lincoln Experimental Satellite 1) – Audio example over here [link to example] thanks to Phil Williams. Others are just a spooky hauling sound like LES-1, NOAA’s etc due the Voltage fluctuation from the solar panels. DD1US does have a very nice collection images and orginal sounds on : [space sounds] A list of frequencies and more in depth details can be found on Mike Kenny’s excellent website: [mike kenny’s website] My TLE containing all current Deadsatellite’s is available on dropbox for anyone would like to try out – [TLE file] Updated once a week. You can use it in your favorite tracker, i prefer Gpredict for this course of the unstable frequency and Doppler effects Orbitron will not always suite on this birds.