RTL-SDR for NOAA15/18/19 Satellite Weather_a


In previous posts several years ago, I looked at receiving NOAA15/18/19 satellite weather using various configurations with a Windows 10 laptop and a RaspberrPi4 (Ref.1/4). To bring in the new year, I thought I would check out the latest reception.

Equipment Setup

Fig.1 Equipment Setup for Reception of NOAA Satellite Weather

Figure 1 shows the equipment setup for receiving NOAA15/18/19 satellite weather. In order to receive signals of adequate strength, a LNA/BPF is required. A 1/4 wave Vee dipole is used with a version 3 RTL-SDR with BiasT to power the LAN/BPF. Signals are received on SDR# and saved as .wav files (Ref.5). These files are then the input to the noaa_apt (Ref.6). & wxtoimg (Ref.7) decoders.

Satellite Tracking

Fig.2 N2YO NOAA18 Polar Orbit Jan5_2024_11:16/11:22EST
Fig.3 Gpredict Showing Entry of NOAA18 Over the Horizon

Figure 2 shows N2YO tracking (Ref.8) of NOAA18 for Jan 5th starting at around 11:16EST local time in Toronto. Figure 3 shows Gpredict tracking (Ref.9) for NOAA18 as well. This shows a planar compass with elevations as well important data such as Azimuth, Elevation, Slant Range, Altitude, Velocity and Doppler Shift @100MHz.

Satellite Reception SDR#

Fig.4 SDR# NOAA18 N Positive Doppler Shift
Fig.5 SDR# NOAA18 NE Positive Doppler
Fig.6 SDR# NOAA18 SE Negative Doppler Shift

Figure 4 shows reception on SDR# just as the NOAA18 appears above the horizon in the N. SDR# is set to WBFM with an initial BW of 50KHz. The audio is recorded as a .wav file. Figure 5 shows a strong signal at the NE and Figure 6 shows a weakening signal at the SE. Note that my view is to the East, with large condos blocking the Azimuths > 90deg. Note the positive Doppler shift when approaching from the North and negative Doppler shift when leaving to the South.

Signal Decoding

Fig.7 Normalize WAV file in Audacity – Ctrl+A – Effects/Amplify
Fig.8 WAV File Processed by noaa_apt Decoder
Fig.9 WAV File Processed by WxtoImg Decoder

Once the WAV file is saved from SDR#, open it in Audacity, select the track [ctrl+A] and use Effects/Amplify to normalize it from +1/-1. Then it can be opened in noaa_apt and decoded/processed as well as in WxtoImg. Since my horizon is visible only to the East and blocked by many buildings especially to the South the results are noisy in places.

Signal Analysis

Fig.8 APT ASK Modulated 2400Hz tone

The WAV file can be expanded in Audacity to show the APT signal structure as in Figure 8 and explained in Ref.3. I find the Doppler shift interesting. Einstein says that the speed of light is absolute, so signals from NOAA18 should arrive at exactly the same speed as it approaches and recedes. This doesn’t happen. According to classical physics for a moving source:
vs=velocity of source=7Km/sec approx
c=speed in medium=3*10^8m/sec
On approach the Doppler shift measured 137916.3-137912.5=3.8Khz which is close.

Fig.9 YouTube Video RTL-SDR for NOAA15/18/19 Satellite Weather_a

Please send your comments, questions and suggestions to:

YouTube Channel
YouTube Channel


#1. – “RTL-SDR for NOAA Satellite Weather on RaspberryPi4”

#2. – “Reçepcão de Meteorologia por Satelite NOAA18 “

#3. – “APT – Automatic Picture Transmission for NOAA Satellites – Scicos/Gnurc Simulation”

#4. – “RTL-SDR for Satellite Weather on SDRangel”

#5. – “SDR#”

#6. – “noaa_apt Decoder”

#7. – “WxtoImg Decoder Restored”

#8. – “Live Real Time Satellite Tracking”

#9. – “Gpredict 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.