Comparing Shortwave Antennas With RTL-SDR And Python

Measuring the efficiency of antennas in absolute terms, which can include very expensive equipment and specialized facilities. For practical applications, especially when building antennas, comparing performance in relative terms is more practical. Using cheap RTL-SDR switches and Python, [Eric Urban] is able to compare performance of two shortwave / high frequency antennas and documents the whole process.

The two antennas in question were a single-band inverted L and a smaller broadband T3FD antenna. [Eric] for the first time collected performance data for each for several days connected to individual computers with RTL-SDRs through low-pass filters. They were set to accept FT8 broadcasts, a popular digital radio radio mode that allows [Eric] for full automation of data collection. GQRX, a software receiver, converts the signals into audio, which is then translated into WSJT-X for demodulation.

The data for each received transmission of FT8 was saved in a log file. [Eric] it also modified the GQRX and WSJT-X to give it all the remote control functions it needed to automatically change frequencies. More than 100,000 FT8 transmissions were registered between the two antenna settings. Using the recorded data and Python, it compares the number of transmissions received, the distance and the title to the transmitters, using the location information included in many FT8 transmissions. When the same transmission is received by both antennas, the signal-to-noise ratio is compared.

From all this data, [Eric] was able to learn that the inverted L antenna performed better than the T3FD antenna on three of the four bands that were tested. He also found that the inverted L appeared to be “deaf” in one particular direction. Although the tests were not perfect, it is impressive how much practical data [Eric] managed to assemble with cheap hardware.

Some other homemade antennas we’ve covered recently include a hybrid spiral for the use of a geosynchronous radio repeater for ham, an outside the center dipoleand a directional antenna made of coat hangers. So go ahead and try to tame the black magic of RF!