# RTL-SDR for LEO L Band Doppler Shift

## Introduction

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

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

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:
f_doppler=[vs/(c-vs)]*fsource
vs=velocity of source=7Km/sec approx
c=speed in medium=3*10^8m/sec
fdoppler=[7*10^3m/sec/(3*10^8m/sec-7*10^3m/sec)]*1.5445*10^9=36KHz

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

contact:

## References

#1. – “RTL-SDR for NOAA 15/18/19 Satellite Weather on SDRangel”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-noaa15-18-19-satellite-weather-on-sdrangel/

#2. – “RTL-SDR for Satellite Weather on GOES16 – Planning”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-satellite-weather-on-goes16-planning/

#3. – “RTL-SDR for Inmarsat Satellite – Planning”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-inmarsat-satellite-planning/

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