Tagged: HF

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

Airspy HF+ Discovery: Collection of Tests and Reviews

The Airspy HF+ Discovery is a new US$169 software defined radio that recently began shipping. On HF it can tune from 0.5 kHz to 31 MHz, and on VHF from 60 to 260 MHz.

It is advertised as having extremely high dynamic range and sensitivity, comparable to high end (and much more expensive) SDRs. High dynamic range means that extremely strong powerhouse stations will not block weaker stations from being received. On lower end SDRs strong stations can cause an SDR to overload, resulting in poor reception.

The HF+ Discovery is an improvement over the original HF+ (now known as the HF+ Dual Port). Back in 2017 we reviewed the original HF+ and found it's performance to be excellent. However, a number of people found that by using low loss preselectors the performance could improve the performance even further.

Originally Youssef (the developer of Airspy products) began designing a low cost preselector add on for the HF+ Dual Port, in order to increase the already great dynamic range. However, it was deemed too difficult for users to retrofit their devices. The result was the creation of the HF+ Discovery, which combines these preselectors with the already excellent HF+ SDR circuitry. Compared to the HF+ Dual, the Discovery is much smaller, and comes in a plastic case rather than a metal one. Instead of the split HF/VHF dual ports seen on the HF+ Dual, the Discovery only has one port that covers both bands. Overall performance with the preselectors is increased, and the price is even lower than the HF+ Dual Port.

Over the past few weeks a number of reviews and comparison videos have come out. Below we list a few that we found interesting.

In this video, the Techminds YouTube channel gives an overview on what the HF+ discovery is, and then gives a quick demo. If you haven't heard of the HF+ Discovery before then this is a good introduction.

Airspy HF+ Discovery - Overview & Brief Testing

The following video by Leif (sm5bsz) is the most technical, as he performs sensitivity and  dynamic range lab tests on multiple SDRs including the Microtelecom Perseus, Airspy HF+ Dual Port, Airspy HF+ Discovery, Airspy Spyverter plus Airspy, SDRplay RSP1 and AFEDRI SDR-Net.

If you want to skip the testing procedures, a summary of the results are presented at 16:20,  31:06, 38:19, and 53:55 video time. In most tests the HF+ Discovery is the second best, after the Perseus.

The first in a series of videos that compare the dynamic range of six receivers: Microtelecom Perseus, Airspy HF+ Dual Port,, Airspy HF+ Discovery, Airspy Spyverter plus Airspy, SDRplay RSP1 and AFEDRI SDR-Net. Here blocking and second order intermodulation is studied with signal generators. Attenuators are used to make the noise figure 26 dB of all radios at the output of the 6 port Wilkingson splitter. This video is for dynamic range on 7.2 MHz. The Discovery is a pre-production unit and the noise figure is a little higher than that of regular production units for unknown reasons.

rx7compare-part1

In this article over on the SWLing Blog guest poster Guy Atkins submits a comparison video between the Airspy HF+ Discovery and an Elad FDM-DUOr ($899). Results appear to show that the HF+ has close to identical performance.

AirSpy HF+ Discovery: First Impressions on Medium Wave vs. Elad FDM-DUOr

Over on YouTube icholakov has posted two comparison videos. In the first he compares the HF+ Discovery to the HF+ Original. In the second video he compares the HF+ Discovery against an SDRplay RSP1A.

Airspy HF+ Discovery SDR vs. HF+ Original SDR - Blind Test

Airspy HF+ Discovery vs. SDRPlay RSP-1A on Medum Wave and Short Wave

We've posted about this review before, but it's still one of the best. Here Fenu-Radio compares the HF+ Discovery against a very expensive Winradio G33DDC and posts multiple comparison audio files. He concludes that the HF+ Discovery compares favorably to the WinRadio.

In this post, Arctic DX measures the sensitivty of the HF+ Discovery, providing a very useful sensitivity comparison table against multiple other SDRs. The HF+ Discovery comes in with excellent numbers.

Over on Twitter there has been a lot of activity too. In the following Tweet, Simon Brown, author of the popular SDR-Console V3 application notes that the HF+ Discovery is virtually immune to strong signals.

We've also seen how the HF+ Discovery's LF performance is so good that it's possible to simply connect a photodiode and see the light spectrum produced by CFLs.

PEPYSCOPE: A Simple Panadapter for HF Radios using RTL-SDR Direct Sampling

Over on GitHub user mcogoni (Marco/IS0KYB) has recently released a new program called Pepyscope. Pepyscope is a simple and fast panadapter application that is designed to be used with direct sampling capable RTL-SDR's such as our RTL-SDR Blog V3 units. Like other panadapters you simply connect the IF output from the hardware HF radio into the input of the RTL-SDR. Then Pepyscope gives you a waterfall display that helps users to easily visualize the spectrum.

Pepyscope is open source and runs on Linux PCs. So far Marco has tested Pepyscope with a KENWOOD TS-180S (single conversion with IF at 8.83 MHz) and an RTL-SDR v3. He has also uploaded a demonstration video on YouTube.

PEPYSCOPE: a simple panadapter for Linux and the RTL-SDR in direct sampling mode

SDRplay RSPDuo Diversity: Combing a Magnetic Loop and Miniwhip Antenna

The SDRplay team have posted some more videos that demonstrate the SDRplay Duo's diversity function. The SDRplay RSPDuo is a 14-bit dual tuner software defined radio capable of tuning between 1 kHz - 2 GHz. It's defining feature is that it has two receivers in one radio, which allows us to combine the signal from two antenna together.

In the video Jon uses a Wellbrook Magnetic Loop antenna and a Bonito Miniwhip antenna both connected to the RSP Duo. Individually each antenna receives the signal relatively poorly and fades in and out as conditions and signal reflections fluctuate. However, with diversity enabled the SNR is improved and fading is significantly reduced.

The method they use to combine signals is a relatively simple method called maximum-ratio combining (MRC). The idea is that the two signal channels are added together, with the currently stronger and less noisy channel having increased gain. So while the signal levels fluctuate, as long as one antenna can receive the signal you will see no fading.

SDRplay HF Diversity Demo

SDRplay note that the key to a good setup is to have the antennas spaced out at a quarter wavelength of the signal frequency that you are receiving. In a second video they show how to properly set up an antenna system for proper HF diversity receiving.

This video demonstrates how SDRuno diversity and the RSPduo can bring enhanced reception at HF using 2 antennas separated by approximately a quarter wavelength. It uses the the current version of SDRuno (V 1.32) and the dual tuner RSPduo SDR from SDRplay.

In this experiment we had a wire dipole with one leg approximately a quarter wavelength from a Boniwhip vertical - both were picking up similar strength signals before going into "diversity" (max ratio combination) mode.

The benefits of diversity tuning at HF are very dependent on many variables, most notably the changing nature of the reflected signal path and the degree to which noise and unwanted signals are not as coherent as the wanted signal.

Antenna and SDRplay set-up for HF diversity reception (rev1)

Fenu Radio Reviews the Airspy HF+ Discovery

The Airspy HF+ Discovery is a smaller, lighter and improved version of the Airspy HF+ which is an HF and VHF SDR with very high dynamic range. The Discovery builds on the HF+ by adding low loss preselectors. This increases the dynamic range even further, and allows the Discovery to compete with some very high end (and much more expensive) SDRs.

Currently the Airspy HF+ Discovery is available for preorder for USD$169. There have been a few delays in getting the unit out, but it appears that the Airspy team will begin shipping very soon.

Over on his blog, radio product reviewer Fenu-Radio has received an Airspy HF+ Discovery, and has given it an in depth review and put it through several real world tests. Fenu-Radio notes that while the initial prototype unit that he received had some issues with overload above 19 MHz, the latest production version has completely remedied this, resulting in impressive performance that competes favorably with the high end USD$2000 Winradio G33DDC software defined radio.

In the review Fenu-Radio compares the Discovery against the G33DDC and finds absolutely no difference in performance between the two. In the review he's also uploaded several audio comparison samples so that you can hear for yourself how identical the two radios are.

Fenu-Radio's Airspy HF+ Discovery Review Unit
Fenu-Radio's Airspy HF+ Discovery Review Unit