Monday 3 August 2020

Range Testing RF Low Noise Amplifier (LNA) for ADS-B data on RTL-SDR

Hi there, I hope you are all well and finding time to be productive and creative in this interesting year, I am sure there are ways to distract yourself from the craziness and also the mundane and what better way than helping yourself to discover all those niche projects that you always put to the back of the queue while you followed the buzz of 'A.i.' Robotics and UAVS.

One project that has interested me over the past few months has been finding some purposeful uses for my RTL SDR dongle. One of those generally straightforward ways is to capture and analyse ADS-B data of nearby aircraft flying overhead.

For my project I am using:
USB RTL SDR HF Box - I find this works ok for the price, it allows me to learn about both Broadcast FM frequencies, 2m HAM, and AM frequencies on the HF Band. Researching on the internet there are some reviewers claiming this box fails to function on HF but mine works fine, you just have to select to correct setting on your computer software of choice.
DIY 1090Mhz Quarter Wave Groundplane Antenna - I made my own, it is quick and easy to do and you will be surprised by the improved results using your new antenna which is made to the correct frequency of ADS-B 1090mhz, you can make an accurate calculation for your antenna here. I used 2mm copper wire from 240v Earth Wire. I designed and 3d printed the covers for the wire to keep them from gouging anyone, I figure it makes it look Sputnik-like too. Notice also, that I added a couple of Ferrite Chokes to the usb cable which plugs into the RTL SDR, i'm not sure how well they work as I have no way to test it but hey why not. The Coaxial cable I used is RG174.
As I don't have an Antenna Anlyzer I have to rely on the correct calculations and trust it.

Low Noise Amplifier (LNA) - I used a cheap one from ebay, there are multiple options of LNA, they can be had for cheap if you look around.
ADS-B Software - There are several options and they all are useful in their own way, depending on which operating system you are using. Generally I like to use Dump1090 on MacOS or Windows. For this test I used a simple option of my smartphone with an app called ADSB Receiver which will give you a maximum range circle for your range test. I connected the RTL-SDR box using a usb otg adapter.
DUMP1090 browser view

Dump1090 Command Line View

So, here we go, we have all of our equipment ready and connected, making sure you have the correct orientation of our LNA so as no to damage the RTL-SDR Box. Check it is correct before powering things.

First of all I tested with the standard antenna that came with the RTL-SDR box, I have no real knowledge of what frequency it is tuned to, I just plugged it in as it is the first port of call for most SDR users new to this.

Opening up Avare ADSB app on Android Phone, after some time I found a few Airplanes, and the app projected my maximum detection range as 18 miles. I thought this was not bad for a first try with just a smartphone and box. However, next I tried with the Homemade 1/4 wave groundplane antenna hooked up.

36 miles which is double the range than with the unknown included antenna. I felt quite pleased to capture aircraft data out at sea from just my bedroom window.

Onto the next step, I added the Low Noise Amplifier LNA to the chain, powered it up using +5v Usb
Far greater increase in range, I am almost receiving from Dublin Airport across the Irish Sea. I was quite excited by this improvement and began to wonder and consider how the LNA could be used for other experiments. Perhaps it will allow me to start receiving Weather Satellite data with a tuned QFH.

Next day I tried to use the LNA setup again, but unfortunately it appeared to have stopped working. I desoldered the metal cover plate to take a look at the components
LNA without cover

Closeup inspection shows a burn on the copper trace and possibly the SPF5189 module. I tested continuity using my multimeter and sure enough it seems there is a problem.

To fix this issue, I could buy another LNA, or I could order a SPF5189 and repair the board so Whatch this space. I really feel the LNA is a benefit to receiving ADSB data and it is not an expensive thing to obtain.

Thanks for reading and I hope you are all well.

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