Tagged: amateur radio

A Pre-Built Raspberry Pi Image for using an RTL-SDR as an APRS RX iGate

Keith Maton (G6NHU) wrote in and wanted to share his new ready to go APRS RX iGate image for the Raspberry Pi. APRS stands for “Amateur Packet Reporting System”, and is a type of packet radio communications system used by Amateur Radio operators. They often use them to transmit short mail messages, weather sensor updates, track vehicles and for various other purposes. An iGate allows APRS messages to be transmitted over the all world via the internet via a signal chain such as: RF->iGate RX->Internet->iGate TX->RF.  To run an iGate you should be a radio amateur with a callsign. A global aggregation of APRS broadcasts received by iGates can be seen at aprs.fi.

An RTL-SDR can be used to receive APRS packets easily and many amateur radio enthusiasts have been setting up APRS RX only iGates using the “direwolf” decoding software. Keith’s image simplifies the process of installing and configuring software significantly by proving a plug and play image that you just burn to an SDcard and plug into your Raspberry Pi. His post also explains how to configure the iGate correctly.

iGate Raspberry Pi Image Running
iGate Raspberry Pi Image Running

A Tutorial on Receiving WSPR with an RTL-SDR V3

Over on YouTube user Veryokay has uploaded a video that shows how he uses the HF direct sampling mode on one of our V3 RTL-SDR’s to receive WSPR signals. WSPR (pronounced “Whisper”) is short for Weak Signal Propagation Reporting, and is a HF ham mode typically run on very low power levels such as 1W. The data from WSPR reception can be used to determine how good or bad HF propagation is currently around the world as each WSPR message contains the callsign, 6-digit locator and the transmit power level used.

For the antenna Veryokay uses a simple random wire antenna directly connected to the SMA port of the V3 up on top of the roof of his apartment building. This gets him reception good enough to receive many WSPR signals. Then together with SDR#, VB Cable and the WSPR-X decoder software, signals can be received and decoded.

He has also uploaded a document detailing the instructions in text and image form at bit.ly/wspr-rtlsdr.


Two Videos Showing the LimeSDR on HF in SDR-Console V3

The LimeSDR is a RX/TX capable SDR with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and 61.44 MHz bandwidth. It costs $299 USD and we think it is going to be an excellent next generation upgrade to SDR’s with similar price and functionality like the HackRF and bladeRF. Back in August we posted how they had added HF functionality to their drivers, and posted some videos from LimeSDR beta tester Marty Wittrock who had gotten HF working well  in GQRX.

Now that SDR-Console has added support for the LimeSDR and HF reception, Marty has uploaded two new videos showing it in action. The first video shows some SSB reception on 40M and the second shows some CW reception on 20M. Marty runs SDR-Console on a MSI Core i5 Cube PC. Marty also writes:

Even with the ‘older’ LimeSDRs that I have that don’t have the proposed modified matching networks on them the performance at 20m and 40m was actually REALLY good for voice and CW. Obviously if the band conditions for 15m and 10m were better the days that I tested the LimeSDR it would have been even better since ‘as-designed’ matching networks seem to do better at 30 MHz and up. Checking the performance at 162.475 MHz (my local Cedar Rapids, Iowa NOAA Weather Station) the performance is excellent on a VHF antenna.



Using a direct sampling enabled Airspy as a Panadapter for a Yaesu FTDX-5000

Tim Havens is an avid CW operator on the ham bands and primarily uses his Yaesu FTDX-5000 transceiver for this purpose. At the same time he also uses a software defined radio coupled with an upconverter as a panadapter by connecting the SDR to the 9 MHz IF output of the Yaesu.

However a problem Tim encountered was that the frequency drift of any SDR he tried was too large, even with a TCXO based software defined radio (like a modded RTL-SDR or the Airspy), and that it was a constant hassle to recalibrate. Furthermore, he noticed that the upconverters he used introduced their own drift which just added to the overall frequency drift.

To get around this Tim decided to use the Airspy in a special configuration. First he used the external clock input of the Airspy to connect to his Jackson Labs “Fury” GPSDO. This device uses GPS satellites to generate a very accurate 10 MHz clock, with almost zero drift. Secondly, to get around the need for an upconverter with it’s own frequency drift he used the ADC1 direct sampling input ports on the Airspy to connect to the 9MHz IF output of his FTDX-5000 through an extra band pass filter and LNA.

Tim writes that he will soon update his post with more images and a video.

Airspy with external GPS clock and ADC1 output connected.
Airspy with external GPS clock and ADC1 output connected.

Listening to a Radio Amateur Stratosphere Balloon with an RTL-SDR

Over on YouTube user kpappa has uploaded a video showing his reception of the J43VHF radio amateur stratosphere balloon with an RTL-SDR dongle and discone antenna. On the 10th of May radio amateurs in Greece launched a high altitude balloon. The balloon carried a transceiver payload which allowed amateurs to talk to each other via the balloon at a frequency of 144.200 MHz. The video shows good reception of the balloon and also shows it’s tracking via APRS.fi.

More information about the balloon can be found at https://j43vhf.wordpress.com/ and http://hellashab.blogspot.gr/.

The high altitude balloon's radio payload recovered after landing.
The high altitude balloon’s radio payload recovered after landing.

Listening to FreeDV Digital Speech with an RTL-SDR

Over on YouTube user BSoD Badgers has uploaded a video showing his reception of FreeDV digital speech at 14 MHz. He uses SDR# combined with the FreeDV software to decode the signal.

FreeDV is a open source software application that allows digital speech to be sent at HF frequencies in a 1.25 kHz wide signal. The same software can be used on the receiving end to decode the signal into speech.


Receiving Hellschreiber with the RTL-SDR and an Upconverter

Over on YouTube user BSoD Badgers has uploaded a video showing reception of Hellschreiber on HF at 20m. To receive the HF frequencies he used a ham-it-up upconverter. He used SDR# to receive the signal and the Fldigi decoding software to decode the signal.

Hellschreiber is a fax-like communications mode used by amateur radio hobbyists.


Understanding Filtering in an Upconverter for the RTL-SDR

Over on YouTube user w2aew has uploaded a video tutorial explaining how filtering in an upconverter works. In a previous video w2aew explained how a simple upconverter for the RTL-SDR worked and noted that for best performance the upconverter needs three filters, one preselector at the input, one after the local oscillator and one after the mixing stage.

In this video w2aew takes a Nooelec Ham-it-up upconverter which has the three filters mentioned above implemented and scopes the output after each filter to show their effect on an input signal.