Category: HF

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

SignalsEverywhere: Creating a DIY Upconverter with a HackRF and RF Mixer

Over on YouTube Corrosive from the SignalsEverywhere channel has uploaded a new video showing us how you can make a DIY upconverter using a HackRF as a signal source and a cheap $10 RF Mixer. An upconverter converts lower frequencies into higher frequencies. For example, an upconverter is commonly used to convert HF signals into VHF, so that VHF/UHF only SDRs can receive HF.

In the video he uses the HackRF as a local oscillator source, a cheap RF mixer on a breakout board, and an Airspy as the receiver. In most circumstances if you needed and upconverter you'd just purchase one like the Ham-it-up, or the Spyverter for ~$40. However the interesting advantage of using a versatile signal generator like the HackRF is that it results in an upconverter that can upconvert HF to almost any frequency. Even without any filtering (which is recommended to remove signal images), Corrosive fings that he has excellent HF reception.

This video is an excellent way to learn about how upconverters work.

HackRF and RF Mixer = DIY RTL SDR Up-converter | Basics of the Passive ADE Mixer

 

LimeRFE WSPR Tests

The LimeRFE is a power amplifier and filter bank solution designed for the low cost TX capable LimeSDR software defined radios. It has multiple bands from HF all the way up to 3.5 GHz, and is capable of putting out about 2W on the HF bands. Currently LimeRFE is crowdfunding over on CrowdSupply with a cost of US$599 or alternatively there is now a cheaper unit for US$449 without support for the cellular bands. The campaign is active for 4 more days from the time of this post, and after that the price is due to rise by another US$100.

The team at LimeMicro sent a unit to Daniel Estévez (EA4GPZ) for testing, and he has recently posted about his results and thoughts when using the LimeRFE for WSPR transmission with a 15m long wire antenna. Daniel connected his LimeRFE to his LimeSDR and used WSJT-X piped into SDRAngel via Pulseaudio to transmit WSPR on the 10m band. He notes that for lower bands, the LimeRFE will still need additional low pass filtering to attenuate harmonics. SDRAngel cannot yet control the LimeRFE so he also created a simple Python script for this purpose.

Unfortunately Daniel's unit only achieved 25dBm instead of the advertised 33dB, but in LimeMicro's post they note that they believe that this is due to shipping damage. However, even with only 0.3W power, Daniel's transmissions from Madrid were able to be picked up in the Canary Islands, Netherlands and Northern England.

WSPR Range with a LimeRFE (reduced 0.3W output)
WSPR Range with a LimeRFE (reduced 0.3W output)

YouTube Review of the RS-918: A Chinese Clone of a Clone of the mcHF SDR

Over on YouTube Kevin Loughin has uploaded a video reviewing the "Recent RS-918" which is a Chinese clone of the popular mcHF open source SDR transceiver made by Chris (M0NKA). The mcHF is a well known small and inexpensive home brewed open source HF QRP SDR that was started back in 2013. It's sold either as a kit for 236.82 GBP (US$287), or with metal enclosure at 292.78 GBP (US$354). The kit comes with SMD components already soldered, but you still need to solder the through hole components and assemble it into the enclosure. The RS-918 clone can be found fully assembled as a ready to use product on eBay for approximately US$400.

As the "Recent RS-918" is a commercial Chinese clone of an open source project that has restrictions against commercial use, it goes against the spirit and legality of the licence imposed by the original creator. So based on that Kevin cannot recommend the RS-918 SDR. However, from his review Kevin notes that apart from some burning hot areas on the metal after transmitting, the SDR itself works and has a nice minimal design. The design appears to be based on an older version of the mcHF, so the latest upgrades are not available.

Kevin's review just overviews the RS-918 and doesn't go into depth reviewing the radio. For the rest of his video Kevin discusses the lineage of the RS-918, noting that it is actually a clone of the Ailunce HS1, which in turn is a clone of the mcHF. He then goes on to discuss the mcHF itself, noting that we should support all the hard work that Chris has put in (and continues to put in) to the original mcHF rather than these immoral clones.

Ham Radio - The RS-918 clone of a clone of an outstanding open source SDR transceiver, the mcHF.

SignalsEverywhere: Improving HF Reception with Impedance Matching

This week on the SignalsEverywhere YouTube channel host Corrosive explores why impedance matching matters when trying to obtain the best reception possible. To do this he reviews the NooElec 1:9 Balun, which is designed to convert the (roughly) 450 Ohm impedance of a long wire antenna or ladder line dipole back down to 50 Ohms, which is the standard impedance that an SDR expects. Small amounts of impedance mismatch are negligible for RX, but larger mismatches can result in poor reception.

SDR Nooelec 1:9 Balun | Why Impedance Matters in Radio

Homebrew SDR Transceiver for HF Operation

Traditionally when we think about Software-Defined Radio we’re thinking about little USB adapters that unlock a world of radio in the palm of our hands. This is done by allowing us to directly sample the IQ data from the mixer within the SDR.

However, this isn’t the only way to experience Software-Defined Radio. Ham Radio operator [Charlie Morris] has uploaded a 10 part series on YouTube explaining how he implemented his own HF transceiver, including custom software. Some of the components such as the amplifier and filters are built completely from scratch, other components use a little DSP magic from a “Teensy” microcontroller. 

Charlie actually samples the I and Q data in a similar way that today’s SDRs do and even implemented the transmit side of the radio so he can make contact with other radio operators around the world, and man… it sounds good!

You can find a complete playlist from Charlie with well-explained videos that go over his entire process from planning, schematics, layout and final operation. The channel appears to be quite active and will surely continue to pump out amazing content.

Homebrew SDR SSB Rig - Part 1 Design Ideas and Thoughts

The HAARP Project Explained Simply

Over on YouTube Curious Droid has uploaded an interesting video that attempts to explain the purpose of the HAARP transmitter project. The High Frequency Active Auroral Research Program (HAARP) is an ionospheric research program based in Alaska. It consists of a high power transmitter and antenna array which is used to excite a portion of the atmosphere in order to study the ionosphere and investigate methods of affecting radio communications. Recently HAARP was also used in an art project called "Ghosts in the Air Glow" which saw HAARP used to transmit several audio art pieces.

HAARP has also been a popular target of conspiracy theorists who believe that the transmitter must have some sort of sinister purpose. Curious Droid's video explains the purpose and science behind HAARP elegantly, hopefully dispelling any conspiracy theories.

He also explains where some of the conspiracy theories may have originated from. The original idea that HAARP was based on was a patent claiming the ability of Ionospheric heating to disrupt communications, take down missiles & satellites, affect weather, scan the earth and even affect brains. However, a project with such abilities would require ridiculous levels of electrical power and land space for the antennas, making it very unrealistic.

Why is Project HAARP so controversial?

Decoding FT8 with an RTL-SDR Blog V3 in Direct Sampling Mode

Over on YouTube user ModernHam has uploaded a useful tutorial showing how to use our RTL-SDR Blog V3 dongles for FT8 monitoring. The RTL-SDR Blog V3 has a built in direct sampling circuit which allows for reception of HF signals without the need for any upconverter. FT8 is an amateur radio weak signal digital communications mode which can be received all around the world even with low transmit power.

In his setup he uses SDR# and Virtual Audio Cable to pipe audio to the WSJT-X decoder. His video goes through all the steps and settings that need to be set and then shows a demo of some signals being received. ModernHam also has another video uploaded a few days earlier which is a more general introduction to FT8 decoding.

If you're interested we uploaded a tutorial last year that shows how to set up a Raspberry Pi 3 based FT8 decoding station with a V3 dongle.

Decoding FT8 with a RTL-SDR (Software defined Radio)