Tagged: HF

Decoding Differential GPS (DGPS) with an RSPdx and MultiPSK

Over on YouTube the TechMinds channel has uploaded a new video about decoding Differential GPS (DGPS) using an SDRplay RSPdx SDR. DGPS is a terrestrially transmitted long wave signal that is used to help correct and improve GPS position data calculations which may have timing errors due to atmospheric propagation delays. It works by broadcasting correction data calculated by the difference in received GPS location and the known location of the DGPS transmission site. DGPS is typically transmitted on longwave between 285 kHz and 315 kHz, but in Argentina there are two stations at 2570 and 2950 kHz.

In the video TechMinds explains how DGPS works, and some location around the world from where it is transmitted from. Later in the video he shows a DGPS signal being received by a SDRplay RSPdx SDR, and then show a demo of how it can be decoded with MultiPSK.

We note that there also various other DGPS decoders available including decoders for Android and iOS. A list of decoders can be found on the DGPS sigidwiki page.

DGPS Differential GPS Decoding With RSPdx And MultiPSK

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.

Comparing 4 magnetic loops for hf

The Malachite-DSP: A $195 Russian Made Portable Wideband SDR Receiver with Touch Screen

Over on the SWLing.com blog we've seen news about the release of a new Russian designed and made portable software defined radio called the "Malachite-DSP". The Malachite-DSP is an "all-in-one" portable SDR that is controlled via a touch screen and two control knobs. It covers 0.1 MHz to 1000 MHz with a bandwidth of up to 160 kHz, and the custom software supports all common modulation types. The whole device consumes 300mA and is powered by a Li-ion cell. It's marketed as a modern DEGEN and TECSUN replacement, so it appears to be targeting the HF short wave listening (SWL) customer.

Production appears to be small, with purchasing currently done by contacting RX9CIM, one of the project creators, directly at his email address (details on this forum post). The cost for a fully assembled unit is 12500 Russian Rubles which is 195 USD (not including international shipping). You can also purchase just the PCB without components for 1100 Rubles (17 USD). Importantly the forum post notes to watch out for scammers, who appear to be trying to take fake preorders for the device.

From the components list we can see that this SDR runs on the MSI001 tuner chip, which is the same tuner chip used in the SDRplay line of units. However, unlike the SDRplay units which use a wideband MSi2500 ADC, the Malachite-DSP uses an audio chip as the RF ADC. This provides a 16-bit ADC, resulting in high dynamic range, but at the expense of the available bandwidth which is only 160 kHz. A STM32H743VIT6 with ARM Cortex A7 processor runs what appears to be custom DSP and GUI software. The software doesn't seem to support DRM, but AM, WFM, NFM, LSB, USB are all supported.

The main place for news and discussion on the Malachite-DSP appears to be on a Russian ham radio forum thread. Judging by the fact that the schematic, software and BOM is all freely released, the project appears to be open source. There is also a group on the Russian Facebook clone vk.com where some discussion is occurring.

The YouTube videos below are by a Russian reviewers. Be sure to turn on the YouTube closed captioning and auto translation feature if you want to follow along in English.



The Malachite-DSP reminds us a bit of the unreleased PantronX Titus II SDR, which is supposed to be a low cost (aiming for less than $100 USD) 100 kHz - 2 GHz tablet screen based SDR that was supposed to make DRM reception more popular. However the Titus II hardware has never eventuated since it's initial news in 2016, and at this time appears to be a dead project.

An Active Low Cost HF Loop Antenna Made in the UK

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.

Cross Country Wireless Loop
Cross Country Wireless Loop

Cross Country Wireless Loop Antenna Amplifier VLF test with 1m diameter coax loop

G8JNJ Reverse Engineers and Reviews the MLA-30 HF Loop Antenna

Last month we posted a collection of reviews about the MLA-30 which is a budget magnetic loop antenna designed for receiving HF signals. The overall consensus from the reviews was that it worked decently for the price, but of course could never live up to the high end loops that cost hundreds of dollars.

Recently Martin (G8JNJ) reverse engineered the active circuit used on the loop from photos taken by M0LMK and has made some observations on it's performance, noting that it's design isn't very good. First he notes that the amplifier chip is a Texas TL592B two stage video amplifier which isn't that great for this application. His measurements show an OIP3 of 20dBm, a P1 saturation of -3dBm and a noise figure of 12dB.

Of interest, he explains that the creator of this loop has designed it poorly as the impedance match of the loop to low pass filter is very wrong, resulting in a very poor amplitude/frequency response. He shows how the response can be improved with a few termination resistors, but is still not great.

MLA-30 Frequency Response. Ideally should be flat.
MLA-30 Frequency Response. Ideally should be flat.

If you're interested in a cheap magnetic loop antenna, Martin suggests DIYing the M0AYF design which he says works a lot better.

We note that the "YouLoop" design is also in the works as a product that will apparently sell at close to manufacturing cost. The YouLoop is a passive loop idea by the creator of the Airspy that consists only of a simple 1:1 transformer and coax cable as the loop. It works best with high sensitivity radios like the HF+ Discovery.

Reviews of the Low Cost MLA-30 Wide Band HF Magnetic Loop Antenna

Recently Chinese manufacturers have begun producing a low cost wide band (100 kHz - 30 MHz) magnetic loop HF antenna known as the MLA-30. The loop can be found on eBay for under US$45 with free shipping. In the past wide band HF loop antennas have not been cheap, normally costing $300+ dollars from manufacturers like Wellbrook.

RF signals are electromagnetic waves that consist of an electric and magnetic component.  A magnetic loop antenna mostly receives the magnetic portion of the wave. This is useful as most unwanted interference from modern electronic devices is generated in the electric component only.  So, a magnetic loop antenna may be preferable in city and suburban environments over other antennas like wires and miniwhips. Magnetic loops are also directional, and can be rotated to avoid interference.

One of the biggest costs to a magnetic loop antenna is the shipping, because a large hula hoop sized piece of metal needs to be sent. The MLA-30 cuts costs on shipping by providing a folded up thin loop wire and no physical support for the loop. You are expected to provide your own support, or simply hang the loop wire on something. If you like you can also replace the included loop wire with a larger loop.

The MLA-30 comes with 10m of RG174 coax, is bias tee powered, and comes as a set with a bias tee injector that is powered over 5V USB. We tested our own unit with the RTL-SDR Blog V3, Airspy and SDRplay bias tee's and found that they all worked well instead of the included bias tee. So if you have one of those SDRs using the loop is as simple and neat as plugging it in and turning on the bias tee.

In terms of build quality, the unit is sturdy and the PCB is fully potted and protected against rain/weather. It is yet to be seen how the external screw terminals holding on the loop will age over a longer period of time however.

So how does the very cheap MLA-30 compare to higher end magnetic loop antennas? Below are some reviews by various hams and SWLs. The general consensus is that it works well for the price, but as you'd expect, falters on handling very strong signals and produces a higher noise floor compared to the more expensive loops, especially in the higher HF bands. But overall we'd say that it's probably still better than using a miniwhip, especially in suburban/city environments, and is probably the best compact HF antenna that you can get on a budget.

What's included in the MLA-30 set. Photo from David Day's Review.
What's included in the MLA-30 set. Photo from David Day's Review.

MLA-30 Magnetic Loop Antenna Review and Comparison by David Day (N1DAY)

In this review David compares the MLA-30 against a 30-ft ground loop and a Wellbrook ALA1530-LF. His results show that while the loop is capable of receiving the same signals that the two comparison loops can, the SNR is much lower. He also notes that the much thinner loop wire used on the MLA-30 seems to result in a much deeper null, and that IMD was a problem for him.

Inside the MLA-30 Active Loop Antenna by Matt (M0LMK)

This post is a complete teardown of the antenna. As the PCB is fully potted Matt had to boil down the epoxy in order to get to the actual PCB. He notes that the PCB is a simple single amplifier design with the exposed pot working as a gain control.

Cheap Chinese Magnetic Loop Antenna (MegaLoop aka MAGALoop) MLA-30 by John

In this review John compares the MLA-30 against a $345 W6LVP and Wellbrook ALA1530LN. His findings are very favorable concluding that it is an adequate performer, perfect for cash strapped SWLs.

First hour battle of the antennas W6LVP loop VS MLA 30 loop test by OfficialSWLchannel

This is a YouTube video where OfficialSWLchannel compares his MLA-30 against a W6LVP loop. He notes that his initial testing shows that the MLA-30 performs as well as the W6LVP loop.

First hour battle of the antennas W6LVP loop VS MLA 30 loop test

MLA-30 Loop vs 80M EFHW by Matthew Payne

In this YouTube video Matthew compares his MLA-30 against a 80M end fed halfwave antenna with an SDRplay RSP1a. 

MLA-30 Loop vs 80M EFHW

MLA-30 Magnetic Loop Modifications by Scanner and Sdr Radio

In this video the Scanner and Sdr Radio YouTube channel uses an RSPduo to compare the MLA-30 against a Wellbrook loop. His results show that the MLA-30 definitely has a higher noise floor compared to the Wellbrook, but still receives signals decently although chasing weak signals it's not good enough. He also shows how to improve the MLA-30 by replacing the cheap coax that it comes with, noting that the modification reduced his noise.

MLA-30 Magnetic Loop Modifications


Testing Version Two of the NooElec Balun One Nine

Over on YouTube two reviewers have just uploaded videos showing off version two of the NooElec Balun One Nine. Version one of the Balun One Nine is a balun transformer that can be used with long wire and untuned dipole HF antennas to match the impedance with a 50 Ohm SDR. Matching the impedance results in better HF reception and less noise. While it is a balun and hence designed for balanced antennas like a dipole, it is possible to convert it into an unun for long wire antennas by cutting a trace.

In the first video Corrosive from SignalsEverywhere compares version one with version two. He notes that the new Balun uses a higher quality Coilcraft component, a more sturdy terminal connector and includes mounting holes. He notes that the power rating of the balun should also allow for low power transmission. However, when comparing the two in reception there is little difference in actual results between version one and two. 

In the second video TechMinds provides a similar video and also shows the enclosure that they will be providing in a premium version.

Nooelec 9:1 HF Balun Version 2?

New Balun One Nine Version 2 From NooElec

Hermes Lite 2 HF Amateur Radio SDR Group Buy Now Active

The Hermes Lite 2 (HL2) amateur radio direct sampling HF SDR transceiver board is now active for a group buy over on Makerfabs. The price is $225.70, and there need to be 25 orders before the group buy is confirmed. If confirmed, production will begin on 23 September, with production estimated to take about one month. More information about the group buy available on the Hermes Lite 2 Wiki. The N2ADR filter board for transmitting with the HL2 is also available on Makerfabs for $52.70.

The HPSDR Hermes SDR is an open source amateur radio SDR transceiver project that was released as far back as 2011. More recently Steve Haynal has been working on a Hermes-Lite project which is intended to be an opensource open hardware low cost amateur radio HF transceiver that is based on the HPSDR Hermes SDR project software and FPGA DSP implementation.

The Hermes-Lite is able to be very low cost because at it's core is the AD9866 chip which is a mass produced RF front end (LNA + ADC & DAC) that is commonly used in cable modems. Because it is a mass produced commodity, the chip only costs approx. US$35-$25 on Mouser depending on quantity. The chip has a 12-bit 80 MHz ADC and DAC, meaning that if used without any analog mixer front end (like in the Hermes-Lite) it can receive the entire spectrum between 0.1 to 38 MHz all at once.

The Hermes-Lite is also a lot more than just the RF chip, as it contains a set of switched RF filters and a 5W power amplifier for TX. It also interfaces with a PC via Ethernet and has a built in FPGA for DSP processing.

The Hermes Lite 2 PCB
The Hermes Lite 2 PCB