RTL-SDR for LEO L Band Doppler Shift


Recently my apartment balcony reconstruction was finished and I was itching to use my L band dish again. I read in a newsgroup that the NOAA satellites have an L band transmitter, so I thought measuring the Doppler shift as the satellite comes into view and leaves would be an interesting experiment. Last year I received NOAA weather transmissions on 137MHz (Ref.1), GOES16 (Ref.2), Inmarsat (Ref.3) and the Hydrogen line (Ref.4) on L band.

Equipment Configuration

Fig.1 L Band Equipment JC Blog
Fig.2 Spectrum of Inmarsat LNA/BPF with Whip Antenna
Fig.3 L Band Reception from NOAA 18/19

Figure 1 shows the L band equipment that I have used over the last several years for the reception of GPS, GOES16 and the Hydrogen Line. The Inmarsat LNA covers 1544MHz and the L Band dish also works well at this frequency (Fig.2). Figure 3 shows the receive configuration. The NOAA 18/19 L band transmitter is received on the L band dish which feeds the LNA and then the RTL-SDR with biasT and e4000 tuner. Signals are received on SDR# and saved as raw IQ baseband signals.

NOAA 18/19 L Band Reception

Fig.4 Gpredict Satellite Locator NOAA 15/18/19
Fig.5 N2YO Satellite Prediction NOAA 19 9/7/23/9:58hrs
Fig.6 N2YO Satellite Prediction NOAA 18 12/7/23 at 11:37hrs
Fig.7 NOAA 18 Approaching +ve Doppler Shift
FIg.8 NOAA 19 Receeding -ve Doppler Shift

Gpredict (Ref.5) and N2YO (Ref.6) can be used to predict when the NOAA satellites will pass by your location. I took signal captures on Sunday July 9th at around 10:00 hrs and Wednesday July 12th at 11:40. Figure 7 shows +ve Doppler shift on approach and Figure 8 shows -ve Doppler shift. The shift on approach was about 32KHz.

From Classical Physics for a moving source:
vs=velocity of source=7Km/sec approx
c=speed in medium=3*10^8m/sec

So this approximates what was measured. I am not a physicist, but this seems to contradicts Einstein’s law of relativity.

Fig.9 YouTube Video RTL-SDR for LEO L Band Doppler Shift

Please send your comments, questions and suggestions to:

YouTube Channel
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#1. – “RTL-SDR for NOAA 15/18/19 Satellite Weather on SDRangel”

#2. – “RTL-SDR for Satellite Weather on GOES16 – Planning”

#3. – “RTL-SDR for Inmarsat Satellite – Planning”

#4. – “RTL-SDR for Radio Astronomy – Planning”

#5. – “Gpredict Satellite Tracking”

#6. – “N2YO Satellite Tracking”

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.