SDR with Active Antennas for HF

A couple of weeks ago I started to gather my first experiences with software defined radios (SDR) and active antennas. I started with low investment, using the RTL SDR dongle, but I quickly realized that using the direct sampling mode for HF is not an ideal solution and added the Spyverter HF up-converter.

For my first trials I used a Mini Whip from RA0SMS as antenna, but the results were quite disappointing.


Finally, I ended up with an active loop antenna (see featured image), using the Cross-country Wireless Loop antenna pre-amplifier (10 kHz to 30 MHz version). The pre-amplifier is powered with 13.8 V via a bias-tee. Common mode chokes on the antenna line and all power lines helped to reduce noise, especially on the low bands. This is final hardware setup setup:

The setup is now running 24/7 on a Raspberry Pi 3B+ using GQRX and WSJT-X. I was surprised, how many stations and countries can be decoded down to 80 and 160 m.


Further Information

Talk given during SARTS monthly meeting

PSK reporter link to stations currently received by 9V1KG

Solar Power for portable Operations

Today I tested the first time my new solar power setup for portable operations. I am using a 60 W PowerFilm foldable solar panel and a 5 A MPPT charge controller for a LiFePo4 4S battery. The whole weight is 1600 g including the 5 m connection cable.

60 W foldable solar panel with MPPT charge controller

Hanging solar panel on the balcony – testing

It was cloudy day and the sun was most often covered by clouds. The panel is only exposed to 1/3 up to max. 1/2 to the full sunlight, if it is there.

Using a power analyzer to measure the incoming power and charge.

Using a power analyzer, the data show a 1.4 A peak current and 19 W peak power. I was able to charge 10 Wh in about 2 hours. Next time I will try to get the panel under full illumination in the sun and measure again.

Power Analyzer from Turnigy

The analyzer shows current, voltage and power and in addition peak values for current and power as well as total energy (power integrated over time) in Wh.

Linear Loaded Dipole for 20 m

As the propagation conditions getting worse for 15 m and 17 m, I extended my linear loaded dipole on both sides by 1.8 m in order to cover the 20 m band. SWR is ok without modification of the 1 : 4 transformation line.

Will see, how it works in the upcoming CQWW DX CW contest.

G5RV Measurements

After replacement of my 80/40 m trap dipole with the G5RV antenna, I made some measurements. The antenna has a height of 12 m at the center, and is hanging as an inverted V with both ends still 4 to 5 meter above ground. The symmetric feeder line is connected via a 1:1 balun to 12.9 m 50 Ohm coaxial cable.

Continue reading G5RV Measurements