Tagged: rtl-sdr

Reverse Engineering a Commercial Inmarsat Front-End to use with the RTL-SDR

Over on his YouTube channel Adam 9A4QV has uploaded a video showing a commercial Inmarsat front end which he reverse engineered to use with his RTL-SDR. The front end is a duplexor, which allows both receive and transmit to occur on the same channel, but to use with the RTL-SDR Adam only uses the receive part. Inside the front end is a large cavity filter, ceramic filter, and about 60 dB of total L-band gain from MMIC amplifiers.

In the second video Adam hooks up the Inmarsat front end to his RTL-SDR and home made patch antenna. The results show that the signals are very strong when using the commercial front end. In a previous post we showed Adam’s results with two LNA4ALL amplifiers. The commercial front end seems to give much stronger signals, but the results with one or two LNA4ALL are adequate enough for decoding.

Inmarsat frontend reverse engineering

Inmarsat frontend test

RTL-SDR Stock Antenna Teardown and VNA Measurements

Over on his YouTube channel oh2ftg has uploaded two new RTL-SDR related videos. In the first video he does a tear down on the stock standard antennas that are supplied with most cheap RTL-SDR units. He finds that most are just a simple design, with the center conductor of the coax soldered to the whip, and the shield pinched between a metal plate and the base.

In his second video he measures the stock antennas on a Vector Network Analyzer (VNA). He places the antennas on a reasonably sized ground plane and finds that the antennas are as expected and pretuned to the DVB-T TV band at around 500 – 600 MHz.

Generally the included antennas are okay for receiving strong signals but we recommend getting yourself an outdoor discone antenna, or building a planar disk (pdf) for more serious scanning.

A look inside five rtl stock antennas

RTL-SDR stock antennas measured on a VNA!

Receiving WSPR with a Direct Sampling Modified RTL-SDR

Over on YouTube user Veryokay has uploaded a video showing how he was able to receive WSPR (Weak Signal Propagation Report) signals at 14 MHz with his direct sampling modified RTL-SDR. WSPR is a HF mode designed to be received even if the signal is very weak. It is used to help determine radio propagation conditions. Direct sampling mode allows you to receive HF signals on an RTL-SDR without the need for an upconverter, but it is more difficult to implement and get good results with. To get the best results Veryokay built an add on PCB that fits onto the RTL-SDR which contains and LNA and single ended to differential operational amplifier to amplify and get correct impedance matching on the input.

His video mainly shows how to calibrate the receiver correctly to receive WSPR as incorrect calibration is the most common error when trying to receive WSPR for the first time. In the video he also explains that he is transmitting WSPR himself using his Raspberry Pi and a QRPi WSPR filter shield for use with Rpitx.

Receiving WSPR with the RTL-SDR in direct sampling mode and WSPR-X.
Receiving WSPR with the RTL-SDR in direct sampling mode and WSPR-X.

Receiving WSPR mode at 20m with RTL-SDR dongle in direct sampling

Fan Cooling the RTL-SDR

Over on his Japanese blog Nobu has uploaded a post showing how he modified his RTL-SDR dongle to be air cooled via two small PC fans (post is in Japanese but can be read with Google Translate – right click -> translate to English in Chrome).

By cooling the dongle, and especially the R820T chip, Nobu writes that he sees improved ADS-B decoding performance as his range is increased. Without cooling the R820T chip can get quite hot and causes failing reception at around 1.5 GHz. Passive cooling is usually enough to fix reception at those higher frequencies, but active cooling via a fan can take it further and actually improve sensitivity slightly.

To add to his post, we suspect that the sensitivity of the R820T/2 front end reduces by about 0.5 dB at most when it heats up (after a few seconds), so forced air cooling should be able to improve sensitivity by about this much.

An fan cooled RTL-SDR dongle.
An fan cooled RTL-SDR dongle.

IF Average SDR# Plugin Updated

The IF Average tool is a RTL-SDR compatible plugin for SDR# which allows you to plot an average of the current spectrum shown in SDR#. This is especially useful for radio astronomers who often need to average the spectrum for a long time in order to get a good plot of the Hydrogen Line. Recently the plugin was updated to support newer versions of SDR# and to upgrade some features. Daniel Kaminski, the author of the plugin writes:

I used ultrafast FFT which works on 4k to 512k bit space. With this plugin it is possible to average up to 64000000 samples in real time. XNA allows to shows the calculation results in real time.

To install the plugin you will need to install the XNA Framework 4.0 Redistributable first. Then copy the plugin files over to the SDR# folder and add the “magicline” to the SDR# Plugins.xml file.

The IF Average SDR# Plugin
The IF Average SDR# Plugin

A Demonstration of the RTL-SDR Receiving WiFi and 2.4 GHz ISM with a Modded SUP-2400 Downconverter

Back in April we posted about how KD0CQ found that he could receive signals up to 4.5 GHz with an RTL-SDR by using a $5 downconverter for DirecTV called the SUP-2400. The RTL-SDR can only receive up to a maximum frequency of about 1.7 GHz, but the SUP-2400 downconverter can be modified to convert frequencies at around 2.4 GHz down into a range receivable by the RTL-SDR.

When we first posted the story the instructions for modifying the SUP-2400 to use as a downconverter weren’t uploaded yet, but they are now. The modification requires decent soldering skills as it involves desoldering a few small SMD components and bridging some points with wires.

Over on YouTube user T3CHNOTURK has uploaded a video showing the downconverter in action. With the SUP-2400 downconverter and RTL-SDR he is able to receive some WiFi at 2.447 GHz as well as signals from a wireless keyboard at 2.465 GHz

RTLSDR Receiveing wifi & 2.4 ghz ism band with moded SUP-2400 Downconverter

Building a DIY Powered USB Hub for using an RTL-SDR on a Raspberry Pi

One problem that sometimes arises when using embedded single board computers like the Raspberry Pi is that they often cannot provide enough current to power devices through the USB port.

Over on YouTube user KD9 BVO wanted to use his RTL-SDR with a Raspberry Pi, but found that the Raspberry Pi shut down whenever he plugged it in, due to it using too much current. To get around this problem he decided to build a DIY powered USB hub. This solution allows the RTL-SDR to be powered via the hub itself, rather than through the Raspberry Pi USB port.

In the video he takes an existing unpowered hub and shows how to modify it to provide power directly to the RTL-SDR via an external power supply.

[Bits #4] How to DIY a Powered USB Hub

More L-Band Videos from 9A4QV: Testing 2x LNA4ALL + Filter + Patch, Receiving the Outernet Signal, L-band Filter

Adam 9A4QV has once again uploaded three new videos to YouTube, all related to L-band satellite reception. The first video shows how much L-band reception can be improved by using two LNA4ALL low noise amplifiers together with a filter placed in between them. Using two LNA’s instead of one improves the reception by about 2-6 dB. He also shows that L-band Inmarsat satellite signals at 1.5 GHz can even be received by his 1090 MHz folded monopole ADS-B antenna placed indoors.

The second video shows a reception report of the new Outernet signal. The Outernet signal is a new satellite data service being provided that broadcasts up to date news as well as various files and information such as educational videos and books for people in third world countries without internet. They have said that they are working on free decoding software for their service which should be released soon. The Outernet signal is a bit weaker than typical AERO signals, but can still be received quite easily with an RTL-SDR, patch antenna and 2 x LNA4ALL. The Outernet downconverter mentioned in a previous post should of course also work well.

His third video shows some tests on his L-band filter, showing return and insertion loss.

2x LNA4ALL and L band filter test

L band filter test