Tagged: HF

YouLoop Portable Passive HF/VHF Loop Antenna now Available in our Store

We have recently been able to obtain a small number of YouLoop HF/VHF portable receive only passive antennas that were produced by the owner of Airspy. The YouLoop is available in our store priced at US$34.95 including free worldwide shipping. It comes with the balun "tee" connector, coax inverter, 2x 1m semi-rigid coax cables for a ~60cm loop, and 1x 2m semi-rigid coax for the feedline. Note that US customers may wish to purchase from airspy.us as they have local US stock. We are focusing on non-US orders for this product and we only have very limited stock at the moment - UPDATE: Now out of stock. We have reordered more and should be back in stock by end of March.

YouLoop Portable Passive Magnetic Loop Antenna for HF and VHF
YouLoop Portable Passive Magnetic Loop Antenna for HF and VHF

If you don't know what a "YouLoop" is, it is a simple passive magnetic loop antenna design which consists of a ring of coax cable and a low loss 1:1 or 4:1 balun. The design was recently popularized by Youssef (prog) the owner of Airspy, and he has put up a page explaining how the design works here. Many users on Twitter have been reporting good results with HF reception with the design. It appears to be especially useful in urban environments where there is lots of local noise.

Being passive, it has no amplification and so it works best with a low noise SDR like an Airspy HF+. However we have also found decent results with SDRplay SDRs, and a standard RTL-SDR Blog V3 running in direct sampling mode, although RTL AGC mode needs to be turned on for an extra boost. Improved results can be obtained by using a low cost HF amplifier on the front end, and even our wideband LNA which is advertised as working down to 50 MHz still does actually give a decent boost from 5 MHz and up.

Also the design has some advantages in that it has very low electrical interference pickup, and has no electronics that can overload from signals that are too strong. Overloading from strong signals is something that can easily affect cheap magnetic loop antennas like the MLA-30, and even higher end loop antennas too. Being a magnetic loop, it also naturally filters out electric field interference which is extremely common in urban environments, and is the reason why e-field antennas like miniwhips often perform poorly.  

The antenna is designed to be extremely portable, being lightweight and easy to assemble/disassemble. As such it is not designed to be weatherproof, so if you do decide to mount it permanently please make use of weatherproofing tape.

Unlike fixed magnetic loops, the YouLoop design is also easy to experiment with. By using longer coax cables you can easily create a larger loop which can result in stronger signals. We found that replacing the 1m loop cables with 2m lengths gave quite nice results for us. If you have the space you could try even larger loops too. 

The design also doubles as a great VHF antenna with reception up to 300 MHz possible when used in a folded dipole configuration. To do that, simply flatten the loop into a dipole shape.

Finally, if you prefer the YouLoop can also be constructed by yourself. The Twitter post below shows the basic design. Search Twitter for "YouLoop antenna" for more discussion on the design too.

In the future we hope to offer a comparison between other loop antennas like the MLA-30 and Wellbrook.

Building an Underground Earth Probe Antenna for 0 – 14 MHz TX/RX

Thank you to Jean-Marie Polard (F5VLB) for letting us know about his work in creating underground "earth probe" antennas that work for both RX and TX between 0 - 14 MHz, and are especially good at VLF and below. He writes:

Can't install an antenna at home? Madame refuses the masts, taut son? One solution, The Earth probes antenna.

Our group (https://www.facebook.com/groups/earthprobes/) started in January 2019. At first everyone made fun of me, the professionals called me crazy and today with more than seven hundred members, we installed underground antenna systems and the results are there.

Between 0 and 14MHz, in transmission and reception, it works!

This system dates from 1914/1918 but has been brought up to date.

It doesn't take much to get started, just the urge to try.

Mad of vlf - elf - ulf ? come here https://www.facebook.com/groups/VLF.ULF.ELF/ nearly 1000 members are waiting for you.

So when? Welcome everyone.

To access the Earth Probes and VLF.ULF.ELF groups you'll need a Facebook account. The groups contain a number of research papers documenting the concept, and the photos section. From the photos, an earth probe antenna appears to consist of two long grounding rods spread over a distance, or a grounding rod and long buried wire, combined with a balun.

An example of an underground antenna setup from a 1935 shortwave magazine.
An example of an underground antenna setup from a 1935 shortwave magazine.

Techminds Reviews a HF RX SWL Antenna for Small Spaces and Apartments

Over on his YouTube channel TechMinds has uploaded a video reviewing the X1-HF 1 - 50 MHz Trapped Coil Receiving antenna from Moonraker.eu which goes for £69.95. This is a small electrically short antenna for HF reception which is easy to setup and install, requiring no radials. However, like all short HF antennas it is a compromise.

In the review he uses an SDRplay RSP2 SDR to test HF reception with the antenna. Later in the video he also tests it outside the advertised 1 - 50 MHz range. He concludes that the antenna works very well for it's small size.

HF RX SWL Antenna For Small Spaces And Apartments RTL SDR

A Neat HF SDR Receiver made from an Audio Reverb Chip

Over on his blog, Ray Ring has posted about his neat little "Mini SDRadio" made from an Si5351 clock generator and a FV-1 reverb audio processor chip.

The Spin Semiconductor FV-1 is a digital reverb chip designed for creating custom audio effects in products. As it is a digital chip it makes use of an ADC and DAC, with the audio effects DSP placed in the middle of the chain. However, by using custom code Ray was able to convert the ADC into an SDR by creating custom AM/FM and LSB demodulators on the programmable DSP instead of the audio effects.

His post contains the full schematics, code and PCB files required to recreate his work if desired.

[Also covered on Hackaday]

Demo of mini SDR receiving VOLMET Station

Using an RTL-SDR Blog V3 in Direct Sampling Mode to Receive HF DRM on an Android Phone

Over on the SWLing blog contributor Dan Van Hoy wrote in and shared a report on how he's successfully been able to receive HF DRM 30 digital audio with an RTL-SDR Blog V3 dongle running in direct sampling mode on an Android phone.

To do this he used an Android app called "DRM+SDR Receiver" which is available for US$4.99 on the Play store. The app supports RTL-SDR and HackRF devices. So all you need to do is set the RTL-SDR Android driver to run in Q-branch direct sampling mode, then tune to a DRM signal for it to begin decoding.

A demonstration video uploaded to his Google drive account shows clean decoding of the DRM AAC audio, as well as the app displaying Journaline and live metadata. He notes that his signal was very strong, so he only required a short wire, but DXers would need an appropriate antenna.

DRM Received on an Android phone with an RTL-SDR Blog V3 running in direct sampling mode.
DRM Received on an Android phone with an RTL-SDR Blog V3 running in direct sampling mode.

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.

😲ПРИЕМНИК КОТОРЫЙ ЛОВИТ ВСЁ!!!💥🔝 ЭТО ВАМ НЕ Degen и Tecsun ВСТРЕЧАЙТЕ НОВЫЙ МАЛАХИТ DSP V2💯🆕

SDR приемник МАЛАХИТ DSP

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.