…we have SDR receiving (RX) capability set up.

• For educational purposes: for example when holding courses or open-door days and projects.
• For test purposes: for example, to test our RF transmissions (TX).

Access:

https://sdr.chaospott.de/ or http://kiwisdr.local:8073/

http://openwebrx (local)

from your browser without installing anything.

The SDR receiving end of our shack is composed of 2 receivers:

• „Kiwi“, for High Frequencies i.e. Short Wave, a KiWi SDR v.1.
• „Berry SiDeR“, for HF and VHF, is a solution comprising a SDRplay RSP2 Pro attached to a Raspberry Pi (4 Model B) running OpenWebRX

The KiwiSDR is a software-defined radio (SDR) that attaches to a Seeed BeagleBone Green (BBG) embedded computer. OpenWebRX is a multi-user SDR receiver that can be operated from any web browser without the need for any additional client software, written in python and JavaScript. Both allow access through LAN and optionally through the Internet.

Frequency ranges

• KiwiSDR: 10 kHz to 30 MHz (VLF-HF spectrum)
• RSP2 Pro: all frequencies from 1kHz to 2GHz, from LF through MW, HF, VHF, UHF and L-band.

The concept is „Web-based Shared access“:

• „Web-based“: users do not need to install anything on their PC, all that's required is an HTML5 capable browser.
• „Shared access“: Multiple users can use the same receiver at the same time, and can listen to different frequencies and modes.

Both receivers support simultaneous connections. The Kiwi supports up to four simultaneous connections, each with their own independently controlled audio and waterfall channels. The Raspberry Pi, which only has limited CPU power, should manage four to six concurrent users. One user (i.e. one „profile“) changing band on OpenWebRX changes the band for all other, multiple „profiles“ running simultaneously are possible but require attaching multiple SDR devices.

Both offer signal decoders directly from the browser-based interface without the need to install additional programs on your computer. Some extensions on the Kiwi are:

• signal strength graph
• signal integrator
• IQ display
• Loran-C display
• WSPR decoder

Some extensions on the OpenWebRX are:

• APRS
• DMR
• WSJT-X.

Last but not least, additionally we have:

• RTL-SDR
• Hack RF One

SDR receivers and transmitter, that we use on demand.

We have 2 options in use at different times depending on what we are experimenting. Having two Antenna allows us to attach one or the other antenna to each receiver or additional devices. Great for flexibility.

• A „Mini Whip Active Antenna“
• An „Eggbeater“

Both are located halfway up on the side of the building, inner courtyard. Though not ideal, the position does allow reception, especially of digital modes. Exposition is along the North-South axis.

The Eggbeater Satellite Antenna has a lower noise floor compared to the Mini Whip. It has a Ground Plane and is resonant on 70 cm. We have tested it and has proven itself to be a great omnidirectional base station antenna receiving antenna for all Amateur Radio, Broadcast bands and many services. The ground plane elements under the Eggbeater increase the overall upward gain of the antenna, useful for hearing Satellites and the International Space Station.

The KiWi SDR has a GPS Antenna attached for precise timing.

We have 2 options in use at different times depending on what we are experimenting. A Diplexer and a Splitter. Both allow to attach the same antenna to the receivers. Great for comparisons.

• The DIAMOND MX-62M Diplexer for the ranges between 1.6 MHz and 56 MHz, and between 76MHz and 470 MHz.

• The Diamond SS-500 Wideband Antenna splitter for frequencies up to 500 MHz

The diplexer limits the optimal ranges of the SDRs to an overall smaller bandwidth, this limitation can be overcome by bypassing the diplexer for the required time, at the cost of using one SDR at a time, or by using different antennas. Combinations of both allow to attach additional devices. Both introduce some attenuation, of course.

OpenWebRX is a multi-user SDR receiver that can be operated from any web browser without the need for any additional client software. Requires a computer, an SDR device and network access.

OpenWebRX is designed for public shared access.

OpenWebRX https://www.openwebrx.de/

Images from https://www.openwebrx.de/download/rpi.php

OpenWebRX with RTL-SDR Receiver with Web Interface

https://www.rtl-sdr.com/openwebrx-an-multi-user-rtl-sdr-receiver-with-web-interface/

HackRF One

https://greatscottgadgets.com/hackrf/one/

A list of currently active WebSDR servers is on

http://www.websdr.org/