OpenwebRX project on OK1KKY site

It’s been a few years since I published an article about Remote RX and the OpenwebRX project (1) on Jaroslav OK1CJB website. I mentioned the desirability of building a remote receiver (Remote RX) in an extravillan (outside the urban agglomeration). The whole thing started at the moment when Roman OK1CBR (2) resumed radio amateur activity under the club brand OK1KKY. I was lucky to get in their way. There is a time when we cannot go to club QTH just when we need to, we are active, working people. That’s the reality. The idea of having an RX station, i.e. the possibility to connect at any time, not only from home, but to listen to traffic on the bands at your leisure, was tempting. The membership of the club station quickly understood.

SWL Ondra OK1-36573 “took over” the whole project. For which we thank him! Several variants were considered: KIWI SDR (3), Spyserver (4), SDR console (5) or OpenwebRX (6). KIWI SDR is not a bad solution, unfortunately production has ended. A serious problem appeared in the past, which did not add to the credibility of the project. We immediately excluded SDR Console due to the necessity of having a PC with Windows OS as a server. We prefer Linux distributions and Raspberry Pi solutions for the server. The lack of Raspberry Pi on the market “threw a pitchfork” into the implementation. The solution was found, Ondra cannibalized UNLis’s DeskPi (7), which is a desktop version with Raspberry Pi4 and 1 TB HDD. He also prepared a microSD card with SW from the website (6) created by Jakob DD5JFK. This is a derivative of the HA7ILM work, the same one used by KIWI SDR. The program is freeware, without ads, but it is “Open”, which means that access cannot be encrypted. That is Jacob’s philosophy. A huge advantage is that there is no need to install anything. An ordinary browser is enough, whether you have a Windows or iOS operating system or a Linux distro, Android on a tablet doesn’t really matter. Everything works. In addition, the control is very intuitive.

We have secured the receiver RTL-SDR blog v.3 original dongle (8). We used the vertical antenna Diamond 145/430 MHz (so-called white stick). In the case of the receiver, we rejected cheap RTL-SDR dongles from eBay or Aliexpress. This was due to poor RF characteristics, frequency instabilities, ….What is usable is for $30. SW OpenwebRX from DD5JFK has very good APRS and digi operation decoders, see FT8, FT4. Nevertheless, it is “tuned” more for use on the VHF/UHF bands. I tested that it also works with the vertical, with reception in the 145MHz band, I monitored station R0ISS using APRS operation and also in autumn tropical conditions I read, for example, HB9AXA using FT8 operation (digital operations are not listened to, but read). These were encouraging results. It was Ondra OK1-36573 again who came up with another OpenwebRX Plus derivative (9). The author is Marat Fayzulin. Marat has also developed a thorough online manual (10). I recommend reading! It contains a lot of interesting tips and tricks. SW OpenwebRX Plus has a number of decoders and options that can also be used on short waves. Tom OK1HOL supplied the receiver, a Chinese SDRplay RSP1 clone from BG7YZF (11). Thanks Tom! After HW modifications, when it was found that the inputs are not protected (ESD), they were supplemented with BAV99 anti-parallel diodes. We are aware that a front end RX equipped with only a low pass filter of 30 MHz (low pass filter) is not the best solution. A short-wave 5-band (14/18/21/24/28 MHz) vertical from LZ antenna (12) served as the antenna.

Since Ondra learned how to install several devices – receivers on the Raspberry Pi at the same time, the RTL-SDR blog v.3 with a “white stick” antenna from Diamond served as the second VHF/UHF. I made several printscreens of this set for listening. We will return to this later in the article.

I will give some information about the individual decoders. Air traffic related decoders (HFDL, ACARS, VHDL-2, ADS-B) refer to the Flightaware website. There you can find out the location of the aircraft, the route and a number of other operational information with just one click, if a picture of the aircraft is available, it is published. It pays to be a user “with benefits” (the so-called Enterprise user), then you have access to more detailed information. Benefits can be obtained with a subscription or if you build a “site” and feed data to the Flightaware server. Club station OK1KKY feeds data to Flightaware, the service is available to website visitors without restrictions. The author of the article also feeds privately in the Flightaware network. Of course, we do not share passwords for accessing the Flightaware service. Due to the fact that we are a land-based country in the center of Europe, I have not tried shipping and its communication. River traffic with AIS operation on the Elbe and Vltava is perhaps the only, but minimal, significance. With 2024 we have a more powerful Raspberry Pi5 ordered and paid for, the Diamond “white stick” antenna will be replaced by the Discone broadband antenna we already have in hand. We anticipate further technical changes and improvements. OpenwebRX Plus can also be an ADS-B decoder. Tom OK1HOL suggested plugging in one RTL-SDR RX for ADS-B with the appropriate antenna. This solution will offer the website visitor the opportunity to compare reception with and without multilateration support – MLAT by Flightaware. Therefore, we do not limit the connection time of the OpenwebRX+ project seasson time. The bands in the menu gradually change according to needs and possibilities.

Sample receiving:

The first is Fax, these are fax meteorological maps broadcast by the German service Deutcher Wetterdienst. TX call sign DDH3 (a similar organization in the Czech Republic is ČHMÚ).

DWD therefore Deutscher Wetterdienst broadcasts also RTTY by operating text forecasts. TX callsign DDK9.

The third sample is HFDL reception. This is a short-wave version of the ADS-B system used for transatlantic flights, flights over areas where there is no ADS-B coverage. The HFDL system is used by smaller and poorer airlines. Click on the matriculation in the “Aircraft” column to enter the Flightaware website.

We will move to the VHF “Air band”. Sample reception of the ACARS system.

We will leave out the 2m band, i.e. 145 MHz, the notorious APRS, Packet where there is really intense traffic. We will look at the 70cm band, frequency 433 MHz. This is one of the ISM (Instruments, Sciences. Medical) frequencies, where remote door opening systems, cars, weather station sensors communicate with consoles and other electronic wonders work on the “General Authority”. OpenwebRX+ contains a database of devices that can identify and decode some information. In the demo you can see the reception of the weather station. With this weather station, we are able to identify the type, find out the temperature, humidity, etc.

One final request:

If you hear or see any interesting radio traffic or stations on the club RX, make a printscreen or simply write an email. After agreement with you, we will be happy to publish. We will also be happy for your feedback, ideas and tips. You can use the contact form on our website to get in touch:

And if you are really satisfied, you can pay us for coffee, Thank you!

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