Over on YouTube Mike Ladd (KD2KOG) from the SDRplay technical support team has uploaded a YouTube video showing him running our recently released RTL-SDR Blog L-Band Active Patch antenna on an SDRplay RSP1a. In the video he receives and decodes AERO signals from his car with his RSP1a powering the active patch antenna via the built in bias tee.
If you didn't already hear, we recently released an active (amplified + filtered) high performance patch antenna designed for receiving L-Band satellites such as Inmarsat, Iridium and GPS. The patch is designed to be easily mountable outside on a window, surface, stick, tree branch etc as it comes with easy to use mounting solutions and extension coax, and is enclosed in a fully weather proof plastic cover. If you're interested the product is available over on our store for US$39.95 with free shipping.
You also might want to keep an eye on Mike's YouTube channel, as he notes that in the yet to be released part 2 video he will be giving away the antenna in a competition.
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.
Specifications:
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 Antenna Amplifier VLF test with 1m diameter coax loop
GNU radio is a popular environment for teachers and developers involved in Digital Signal Processing and exploring new radio architectures. For receiver applications, the low cost dongle is a popular hardware choice, but if you need reliable, clean, continuous radio signal reception from 1kHz to 2 GHz (without the need for block converters or external filters) then an SDRplay RSP is a useful alternative.
With help from the GNU radio foundation, SDRplay has now made available a workflow for windows for all its RSP radios: www.sdrplay.com/docs/gr-sdrplay-workflow.pdf
Special thanks goes to Frank Werner-Krippendorf (HB9FXQ) who did the original SDRplay source block development, and to Geof Nieboer who has developed the Powershell scripts which enable operation on Windows.
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.
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.
Leif (sm5bsz)'s series comparing the Airspy HF+ Discovery against various other SDRs such as the Perseus, SDRplay RSP1, Airpsy HF+ Dual, Airspy + SpyVerter and AFEDRI SDR-Net continues again, with parts 3, 4, and 5 now having been uploaded to YouTube. In previous posts we covered parts 1 and 2.
The comparisons are very technically inclined, so may be difficult to follow for those unfamiliar with radio theory. We have highlighted the time stamps where he discusses the results.
In conclusion, for all tests the Perseus always comes out on top, with the HF+ Discovery coming a close second. Generally third best is the HF+ Dual, then the AFEDRI, followed by the Airspy+SpyVerter and RSP1.
Part 3: Here performance with real antenna signals is compared. Attenuators are used to make the noise figure 26 dB of all radios at the output of the 7 port resistive splitter. This video is for dynamic range on 7.2 MHz.
Results @ 30:20
rx7compare-part3
Part 4: Here performance with real antenna signals is compared. Attenuators are used to make the noise figure 27 dB of all radios at the output of the 7 port resistive splitter. This video is for dynamic range on 14 MHz.
Results @ 16:04
rx7compare-part4
Part 5: Here here second order intermodulation is studied.
Over on his YouTube channel icholakov has uploaded a video comparing the USB power consumption of various software defined radios. In his tests he uses an inline USB current meter and compares a Perseus, RSP1, RSP1A, Airspy HF+, Airspy HF+ Discovery, RTL V3, Nooelec RTL Mini, Hauppauge 955Q, Flightaware RTL.
If you're only interested in the summary table, then this can be found at 05:49 in the video.
Generally SDRs with better performing tuners and more amplifiers will have higher power requirements, although current consumption can't solely be used to judge performance as some SDRs like the SDRplay make extensive use of filtering to overcome RX performance issues in their tuner. The RTL-SDR V3 and FlightAware dongles have slightly higher current draw compared to the Mini RTL-SDR as they contain an additional HF amplifier and ADS-B amplifier respectively. Lower power consumption may be useful when used with batteries and mobile phones.
2019: Nine SDR Receivers power consumption comparison - how much power does your SDR consume?
Leif (SM5BSZ) is fairly well known in the SDR community for doing very indepth technical tests of various SDR receivers over on his YouTube channel. Recently he's released part two of a series where he compares the new Airspy HF+ Discovery against various other SDRs such as the Perseus, SDRplay RSP1, Airpsy HF+ Dual, Airspy + SpyVerter and AFEDRI SDR-Net. In the first video he studied the blocking and second order intermodulation effects of each SDR using signal generators. We summarized those results in this previous post.
In the new video Leif compares the dynamic range of each SDR using real HF antenna signals at 7.2 MHz. In order to create a fair test of dynamic range, appropriate attenuation is added to each receiver in order to make their noise figures equivalent, so that the incoming signal strength is the same for each SDR.
The first set of dynamic range results is summarized at time 08:14, and these results show the dynamic range comparisons for strong night time signals. Again like in the other videos the Perseus is used as the reference SDR since it is always the best. The tests show that the HF+ Discovery trails behind the Perseus by only -3dB, followed by the HF+ Dual at -10dB, AFEDRI at -15dB, Airspy+SpyVerter at -18dB and finally the RSP1 at -23dB.
The second set of results is summarized at 17:47 and this includes a day time dynamic range test. The rankings are very similar to the night time test.
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.
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
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 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.
