Downloading satellite images with an RTL-SDR

This is an ongoing post for me because I’m still learning as I go. I’m interested in Sicence and learning, so naturally always been interested in downloading weather satellite pictures from low earth orbit in space. All you need is about £100 worth of equipment to do this and it’s a whole new learning experience.

Please note, that I’m writing this article for Microsoft Windows users. People on Mac / Linux should be able to figure it out, but will need to source the appropriate software for them. There are versions available, but everyone has their own preferences. I’m using Windows, so just listing it for people to help them along.

Along the way I’ve encountered errors and want to help document them and write them down to speed it up for others too.

I’m going to be updating this post over time, as I do different things, so it’s going to be an ongoing topic that’s finished / unfinished. As I’m still learning as I go.

Software you need, and sites you will find useful

Thre are various choices, but these are the ones I’m using. I’ll also include the additional things you’ll probably need troubleshooting

SDRSharp – You can use the standard package (LINK), or the one with recommended plugins (LINK)
Virtual Audio Cable – Needed to convert audio output into an input (LINK)
Wxtoimg – Converts the audio signals into line images from SDR sharp (there are two versions I’ll list here)
- Wxtoimg (Restored) – This is a clone of the original site – Software (LINK), you may need to use the BETA version (LINK)
- Wxtoimg (Volker Wraase) – This is a modified version (I use this one due to the easy way to update keplers) (LINK)
Zadig Drivers – This may be needed if you’re having problems with your dongle being recognised (LINK) –> Run as Administrator
RTLSDR.dll File – This is normally needed to fix the “Device not found” error in SDRSharp (DOWNLOAD LINK TOP RIGHT)
Bias-Tee Drivers – This is needed for software powered BiasTee injection with the dongle and amplifiers (LINK)
Audacity – This is sound software, some people use this due to additional audio filters (LINK – Auto Download)
Orbitron – Useful for tracking with the doppler effect (LINK)

Useful websites for NOAA images

RTLSDR Blog – Gives guides and links to the Dongles
RTLSDR (Reddit Community) – Useful for troubleshooting or sharing your info
N2YO – Tracks satellites, alternative for finding frequencies and their locations

Where can you buy the Dongle?

There are various sites, eBay, Amazon that sell them. Unfortunately there are also a lot of clones out there which whilst do the same thing aren’t genuine. There are also different ones (Nooelec, Hackspy, HackRF), there’s different brands. This is down to personal choice. I decided to buy the genuine RTLSDR Dongle for simplicity (you can find the resellers on the RTLSDR Blog website). As I’m based in the UK, I purchased from their authorised UK Reseller (Technofix) because I wanted a genuine product, and believe in supporting these type of Businesses.

What else can you buy?

If you’re doing NOAA there’s a few choices. Recommended options appear to be LNA4All Amplifiers and DC Blocks and Sawbird+ filters (specifically the NOAA variant). I believe the Nooelec are the genuine resellers for them on the Amazon Link given, so this should be OK to purchase. The list is generally endless, some people use copper ground straps, and vary on designs, but this should help you get started.

I personally have the Sawbird+ NOAA LNA, and the Wideband LNA from RTLSDR, but I get a lot of noise which I’m still learning because I’m experiementing at the moment. Although due to the recommendations of the Sawbird I believe I have the right equipment. I just need to learn how to use it! That’s another article though.

Common problems, questions and fixes

SDR# (SDR Sharp) – Device not found error

Download drivers with Zadig and install them
Install the RTLSDR.dll driver (This fixed it for me, because I already had Zadig drivers installed) you put it into the SDRSharp folder

Recording Volume too low in Wxtoimg (or constantly 5.6)

A constant volume of 5.6 means it’s not receiving a signal, make sure the sound “output in SDRsharp” is set to Virtual Audio/VB Audio
Also check the input in Wxtoimg (Options –> Recording Options), make sure the “Soundcard” option is set to Virtual Audio Cable

Bias-T not working (Software Bias)

Please note, this is applicable to Software Bias-T, if you’re powering it via DC Jack or USB, it’s normally activated as soon as you plug it in.

When I first downloaded the software, I double clicked on the .EXE file, you get a command window but nothing happens. I found running the program didn’t seem to do anything. There was two problems. Firest to run the program, I found it best opening a command prompt and running the program manually.

At first it came up with an error (message below about the udev rules).This is solved by closing down the program that’s currently using the V3 receiver because it’s sharing the device. I had SDRSharp open, so it’s a conflict because the device is already being used.

The next problem was recognising the devices. You do this by simply inputting the command and device number

When I activated it shows up as a Rafael 820T Tuner (same picture above). You may need to experiment with the device number, it will be either 0 or 1. The command above basically says turn bias T off on device 0. To turn bias T on on device 0 it would be rtl_biast -d0 -b1

Sawbird+ not amplifying

If you’re using Bias T, or powering via USB it should do this automatically. I was powering mine via a Bench power supply and found the gain was only about 8dB which seemed to suck since the sawbird is apparently capable of something up to 30dB. Oddly enough this was because of the voltage. The recommended range on the Sawbird is 3.3v – 5v (it has protection circuitry for up to 12v apparently). I was powering mine with 5v DC and the power consumption was 0.15A. Oddly enough I was giving it TOO MUCH power. When I reduced the voltage to around 3.5v the power consumption rose to 0.35A, and I had about 25dB gain. No clue why, but just incase you have this problem too

EDIT – Even then the Sawbird doesn’t seem to amplify properly using my Bench power supply. It’s probably because it’s not a very finely tuned one, or accurate. When I activated BiasT using my Dongle the power light comes on. It’s dim using my bench PSU, could be too little, could be too much. It works using BiasTee anyway, so I’m doing it this way currently.

Lots of spikes in SDRSharp but no signals

From what I read this is down to noise from equipment, it’s better to move further away from the source and use something like an active USB extension cable. The lines should be fairly soft with no spikes from what I’ve seen. Also it may be worth putting the bandwidth to around 35-40kHz in SDRSharp to help filter out the signal.

Poor images, slanted APT image in Wxtoimg

Excluding slant correction (Disable PLL, Image –> Slant Correction). You need to make sure Audio files are processed at a certain sample frequency. These need to be 11025Hz. In order to do this, there’s two options.

In Wxtoimg –> Options –> Sampling frequency, make sure NOAA / Default are set as 11025
In VB Audio Cable –> Right click sound icon –> Audio devices –> Recording –> Click VB Audio –> Properties –> Advanced, and make sure the drop down shows 11025 (mine is set as 2ch dictation). I’m still experimenting, but 11025 is the correct one to use. This is increased my image quality, and I can start seeing the APT image bars now

As you can see in the RTL-SDR / Wxtoimg image below, I’m still getting poor quality, but I’m documenting this to help others. Before I wasn’t even receiving the APT bars, they were just constantly skewed, as my sample rate was about 10900Hz. You will notice in the image the APT bars start curving nearer to the top. I believe this is because of doppler shift, so I’ll need to experiment with something like Orbitron to improve these

Unable to find the waterfall

Having problems finding the waterfall to download images. I found the best way is to get the basic antenna functional first, then by opening your SDR software. I found to move the antenna away and then look for two solid signals at the edges of the screen these are spikes. Then when the timing starts, slowly move your antenna around until you start to see waterfalls being created. Then slowly move your antenna, once it starts getting a stronger signal, you should get multiple spikes appear when it downloads the images. It’s easier finding the waterfall and what it looks like before trying to download it

What side connects to RTL-SDR with an LNA, Input or Output?

The LNA connects to the RTL-SDR via a Coax cable, you should be connecting the “Output” side to the SDR, and the “Input” side to the aerial. If you’re doing Bias-Tee power injection, the Output side that connects to your RTL-SDR gets your voltage from this.

Lots of noise on the line

I’m still working on this. I’m using a Wideband LNA and it seems to pick up a lot of noise from electrical equipment. Although I now have a Sawbird to experiment with too. It’s recommended to run the antenna via an active USB extension cable as they’re less sensitive to interference and outside preferably as close to ground to reduce electrical noise.

Basically it would look something like this. This is the next step I’m going to experiment with

Antenna – short coax run – LNA (like Sawbird) – Short coax to socket – USB extension cable to laptop / computer

Interference / Connection

One of the mistakes I made is to use an LNA filter powered from the Bias-T of the RTLSDR receiver (directly connected to it). Reading on reddit suggests this is a no no, because all that happens is the V3 receiver doesn’t see the shorted signal from the QFH antenna but from the Wideband receiver.

Apparently the suggested connection method is follows

QFH Antenna
QFH Antenna Connects to Wideband LNA
Coax cable connects to Wideband LNA
V3 RTLSDR Connects to other end of Coax cable.
QFH –> LNA –> Coax Cable –> V3 RTL SDR

What pictures or results have I obtained?

My results are poop currently. As I experiment I’ll update the pictures with improved results.

CURRENT SETTINGS I’M USING

I changed the antenna setup a bit, and I’m starting to see waterfall now, I’m still getting noise now, so I’ll be experimeting with setup noted below and trying it outside as Wxtoimg is starting to generate an image for me now (APT I believe – Short for Automatic Picture Transmission), there are high resolution images you can get at a slightly different frequenciy. Baby steps first however

V-Dipole Antenna (aerials set at 120 degrees)
Bandwidth 35kHZ
Sample Rate 1.4 MSPS
Sawbird+ NOAA LNA

As noted above, this is new to me and I’m experimenting and still learning. I know I’m receiving a lot of noise, because I’m not hearing the obligatory waterfall “pinging / ticking” noise when connecting to the NOAA satellites. I just hear a lot of static as it downloads the images. This is more due to noise and signal strenght. You can see below that when decoded I’m getting images, however when the Audio file is played into Wxtoimg with enough volume and no interferance, then it should be almost a live image of the earth from the Satellite.

(This is an example of what it can look like), as you can see. I have much to learn and experiment to learn more.

I’ve currently got a QFH antenna (indoors), but it needs redesigning. The next things I’m going to do / experiment with are as follows

Rebuild my QFH antenna (also another dipole antenna)
Use 50ohm coax cable (not 75ohm like RG6)
Move my equipment outside, and run a USB cable to remove any noise from electrical equipment
Work on improving volume and reducing noise
Experiment with Audacity / SDR Play
- Audacity, people tend to experiment with Filters / Bandwidth before they upload to WXtoimg
- SDR Play, people tend to find better bandwidth, frequencies, decimation and do microtuning