Comparing Four Wideband Magnetic Loop Antennas on HF with an SDRplay RSPduo
Over on YouTube the Scanner and Sdr Radio channel has uploaded a video comparing four different brands of HF wideband loop antennas using an SDRplay RSPduo. The loops he tested include the cheap Chinese MLA-30 (~$40), the Cross Country Wireless (CCW) loop ($70), Bonito ML200 (~$442) and the Wellbrook 1530LN (~$305).
The MLA-30 was slightly modified with the cheap coax removed and a BNC connector added. Each of the antennas used a wire loop with diameter of approximately 1.6m, except for the Wellbrook which has a fixed size solid loop of 1m.
The tests compare each loop against the Wellbrook which is used as the reference antenna. In each test he checks each HF band with real signals on the RSPduo and compares SNR between the two antennas.
The results show that the two expensive antennas, the Bonito and Wellbrook, do generally perform the best with the lowest noise floors, but surprisingly the MLA-30 actually performs very well for it's price point, even outperforming the Wellbrook reference on SNR in some bands. We note that some of the improvement may be due to the larger 1.6m loop size used on the MLA-30, compared to the 1m loop on the Wellbrook.
Also we note that it can be hard to compare antennas in single tests, because the differences in antenna radiation patterns could be favorable for some signals, and less so for others, depending on the location.
The principle of magnetic loops requires a small size in relation to the working wavelengths. Under these conditions the antenna has only the directivity of a magnetic dipole. Consequently, they radiate identically, as long as they are all oriented in the same plane.
The antenna radiation patterns are therefore the same for all the tested loops, and it is only the size of the loop and the quality of the amplifier that makes the difference, at least for frequencies below 20 MHz.
It should be noted that with a diameter of 1.6 meters, i.e. a circumference of 5 meters, the antenna is no longer a real magnetic loop at the top of the HF spectrum (30 MHz, λ=10 m). It becomes sensitive to the electric field, and this can lead to random differences with “real” magnetic loops, which are smaller in relation to wavelength.