Over on YouTube Tech Minds has uploaded a new video where he reviews the MLA-30 active HF loop antenna. In the past we have posted about the MLA-30 antenna a several times on the blog as it is the cheapest active loop antenna available on the market, can be powered by the RTL-SDR Blog V3's bias tee, and generally loop antennas can give good HF performance in a small package. In the video he compares the MLA-30 against an end-fed halfwave antenna and concludes that the MLA-30 works well at the lower frequencies, but not so well in the higher bands.
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.
Cross Country Wireless is a UK based company that has created an active HF loop antenna for only $70 USD including international shipping. The loop appears to have already been for sale for a while now, but recently they've created a new version that can be easily powered by a 5V bias tee with at least a 67 mA current capacity. This makes it very easy to use with radios that have built in bias tee's such as our RTL-SDR Blog V3 and SDRplay and Airspy units. The page reads:
The Loop Antenna Amplifier contains all the electronics needed for home DIY construction of an active loop (magnetic loop) low noise receiving antenna.
The amplifier consists of two units, a weatherproofed outdoor unit for connection to a suitable loop and a base unit to further amplify the signal and to provide DC power up the coaxial cable to the outdoor unit.
The outdoor unit is housed in a polycarbonate box with stainless steel antenna connections and a BNC socket. The indoor unit is a PCB with two BNC connectors and a USB socket to take 5V from a USB socket on a PC or phone charger.
Like our other active antenna products it has RF overload protection to allow it to be used very close to transmit antennas without damaging the amplifier or the attached receiver.
The loop depends on what the user has available. We have tested it with simple wire loops or deltas, coax loops and an alloy loop made from a bicycle wheel rim. We supply a 3m (10 ft) length of wire as a simple loop to make a first loop for testing.
The photograph on the right shows the prototype with a 1m diameter loop of LDF4-50 coax cable as a test loop.
With a simple wire loop or delta and a small USB powerbank it makes a very compact and portable receiving antenna for holiday listening or covert use.
The latest version can now have the head unit powered directly from receivers with a 5V bias-tee such as the SDRplay receivers or some RTL-SDR dongle receivers with a bias-tee option.
- Frequency range: 10 kHz to 30 MHz
- Loop amplifier input impedance: 0.3 ohms
- Output impedance: 50 ohms
- Supply voltage: 5 V from USB socket or charger
- Supply current (head and base unit): 112 mA
- Supply current (head unit fed with 5V bias-tee): 67 mA
- Loop antenna outdoor unit connectors: Two M6 stainless steel threaded studs and BNC female (RF out 50 ohms)
There is no comparison yet that we've seen on how this loop compares against the cheaper US$45 Chinese made MLA-30 loop. In a previous post Martin (G8JNJ) reviewed the MLA-30 and noted several design flaws after reverse engineering the circuit. He has let us know that he will also be reviewing the Cross Country Wireless Active Loop and will let us know his thoughts in the future.