A new reasonably priced 5-band HF preselector has been released by the company Cross Country Wireless, and it looks perfect for use with SDRs. The price is $56.95 GBP, which right now is about $72 USD. They write:
This can be used to provide additional front end selectivity for HF and medium wave receivers protecting the receiver from strong out of band transmissions, wideband noise and other transmitters on multi-station field days.
As the sunspot cycle declines and more listening is done on the lower HF bands with long wire antennas and strong NVIS signals then the HF Preselector is an ideal accessory to aid receiver performance.
It is invaluable when using simple conventional superhet or SDR receivers such as RTL-SDR dongles with upconverters or SDRPlay with large HF antennas.
It is an ideal tool to reduce ADC overload on the Icom IC-7300 with the new second receiver socket modification kit.
It can also be used with other transceivers that have sockets for a separate receiver input and receive antenna output.
It also covers the medium wave broadcast band for MW DXers.
The Preselector is a passive high Q design that does not use an additional amplifier or require external power.
Frequency tuning range: 0.5 to 52 MHz in five bands
Recently DK8OK wrote in to us and wanted to share his latest review of the Airspy and SpyVerter combo (pdf). His review focuses on HF usage and he shows various examples of HF signals that he has received with the Airspy+SV such as the CHU time station, STANAG, DRM, ALE, HFFAX, VOLMET and HFDL. He also shows some tricks for optimizing HF reception, a tutorial on performing multi-channel audio recording and decoding in SDR-Console, a tutorial on playing and analyzing recorded files as well as some examples of weak signal reception.
Overall DK8OK praises the Airspy+SV combo citing it’s excellent dynamic range as one of the reasons it performs so well.
We should note that for prospective buyers, the Airspy team is currently working on a new complimentary solution for HF monitoring called the Airspy HF+. This will have extremely high dynamic range (even higher than the Airspy+SV combo), but it will have a smaller bandwidth. So the Airspy+SV combo will still be the best for monitoring a wide 9 MHz chunk of the HF band, whilst the HF+ will be the best for getting into those very hard to receive signals.
Last month we saw news of the Airspy HF+, which is a yet to be released software defined radio with a focus on high performance reception in the HF bands. Some preliminary specs were unofficially released back then on the Airspy Yahoo forums.
The goal pricing is to be below $200 USD. If this is true, then it will compete heavily with the $249.95 USD ColibriNANO which is another new HF specialty radio with similar specs.
The Airspy team write:
Airspy HF+ is a paradigm shift in high performance HF radio design. It is a joint effort between Airspy, Itead Studio and some famous chip maker to build a state of the art SDR for HF and VHF bands.
Like most high-end HF receivers, the HF+ uses very high dynamic range ADC’s and front-ends. But unlike the current offerings in the market, it also brings more frequency agility by using high performance passive mixers with an excellent overtone rejection structure. Both the architecture and level of integration achieved in this design allow us to bring top performance reception at a very affordable price.
Airspy HF+ achieves excellent HF performance by mean of a low-loss band filter, a high linearity LNA, a high linearity tunable RF filter, an over-tone-rejection (OTR) mixer that rejects up to the 21st harmonic and an IF filter. The 6 dB-stepped AGC gain is fully controlled by the software running onto the DSP which optimizes the gain distribution in real time for optimal sensitivity and linearity. OTR is a key issue in wide band HF receivers because of the large input signal bandwidth. The output of the IF-filter is then digitalized by the IF ADC for further signal processing.
Excellent VHF performance is also achieved by using optimized signal paths composed by band filters, high linearity LNAs with a stepped AGC and an over-tone-rejection mixer and IF filters optimized for their respective bands. The amplifier gain is switchable in 3 dB-steps and is fully controlled by the AGC processing running onto the DSP. The RF signal is converted to baseband by a high linearity passive mixer with overtone-rejection structure. The low-IF signal is then converted into the digital domain by the IF ADC for further digital signal processing.
The IF digital to analog converter has a 4th order multi-bit topology; it features very high dynamic range and linearity. The IF-ADC sampling frequency is determined by a control algorithm running on the DSP. This advanced technique changes the sampling frequency depending on the tuning frequency with the goal of avoiding the disturbances generated by the switching discrete-time sections of the IF-ADC.
Digital Down Converter
Once the IF signal is digitalized, the high sample rate I/Q stream is then frequency translated and processed with cascaded CIC and FIR decimation stages. After every stage, the sample rate is reduced and more the resolution is increased. The final signal at the output has 18bit resolution and the alias rejection performance is 108 dBc. The data is then scaled to 16bit and sent to the Micro-Controller for streaming over USB.
Use it over the network!
Connect as many SDR applications as needed to the HF+, over the Internet or in your own local network with near zero latency thanks to the new SPY Server software. This setup basically brings all the flexibility of Web based SDRs while still benefiting from the full power of desktop applications. The IQ data is processed in the server with state of the art DSP and only the required chunk of spectrum is sent over the network. What is sent is the actual IQ signal, not compressed audio. This means you can use all your favorite plugins to process the IF, eliminate noise and perform heavy lifting of the signals as you are used to do with locally connected SDR’s. We have a tradition of building multi-tools, so we made sure the SPY Server runs on 32/64bit Windows and Linux on Intel and ARM processors without any compromises. Low cost Raspberry Pi 3 and Odroid boards are in the party.
Over on the Airspy Yahoo forums and Twitter we’ve seen news of an upcoming new product from the developers of the Airspy SDR. The new product is called the Airspy HF+ and will be a low cost, yet extremely high performance HF specialty radio.
Smart AGC with real time optimization of the gain distribution
All RF inputs are matched to 50 ohms
2 x High Dynamic Range Sigma Delta ADCs @ 36 MSPS
600 kHz alias and image free output
18 bit DDC
0.5 ppm high precision, low phase noise clock
4 x Programmable GPIO’s
No drivers required! 100% Plug-and-play on Windows Vista, Seven, 8, 8.1 and 10
Industrial Operating Temperature: -45°C to 85°C
Basically, this addresses the lack of affordable and good performing receivers for HF and VHF. Target price < $200
As with all Airspy products the SDR focuses on achieving extremely high dynamic range. From the specs is seems that the dynamic range and image rejection will be high enough so that even extremely strong broadcast AM or FM stations will not require any filtering or attenuation. They are also confident enough to say that no gain sliders will need to ever be adjusted to avoid overload.
For SWLers and MW DXers this seems like the ideal SDR as it should perform as well as high end SDRs like the Perseus, RFSpace and Elad SDRs, but at a fraction of the price.
This year at the end of February HAARP (High Frequency Active Auroral Research Program) scientists are planning to run several experiments that involve transmission. HAARP is a high power ionospheric research radio transmitter in Alaska, which typically transmits in the 2.7 – 10 MHz frequency region. The transmissions are powerful enough to create artificial auroras in the sky. Due to a lack of funding HAARP research was shut down in May 2013, and then later given to the University of Alaska Fairbanks (UAF) in 2015.
UAF plans to activate HAARP again at the end of Feburary, so it seems that it would be interesting to receive the waveforms with an HF capable SDR such as the RTL-SDR v3, or with an upconverter like the SpyVerter. Under some conditions the signal could propagate all over the world. It seems that the researchers are also interested in reception reports from listeners and they plan to post updates closer to the dates of transmission. The full press release reads:
The University of Alaska Fairbanks Geophysical Institute is planning its first research campaign at the High Frequency Active Auroral Research Program facility in Gakona.
The High Frequency Active Auroral Research Program facility near Gakona includes a 40-acre grid of towers to conduct research on the ionosphere. The facility was built and operated by the U.S. Air Force until August 2015, when ownership was transferred to UAF’s Geophysical Institute.
At the end of February, scientists will use the HAARP research instrument to conduct multiple experiments, including a study of atmospheric effects on satellite-to-ground communications, optical measurements of artificial airglow and over-the-horizon radar experiments.
Members of the public can follow one of the experiments in real time. Chris Fallen, assistant research professor in space physics, will be conducting National Science Foundation-funded research to create an “artificial aurora” that can be photographed with a sensitive camera. Observers throughout Alaska will have an opportunity to photograph the phenomenon, which is sometimes created over HAARP during certain types of transmissions.
Under the right conditions, people can also listen to HAARP radio transmissions from virtually anywhere in the world using an inexpensive shortwave radio. Exact frequencies of the transmission will not be known until shortly before the experiment begins, so follow @UAFGI on Twitter for an announcement.
Operation of the HAARP research facility, including the world’s most capable high-power, high-frequency transmitter for study of the ionosphere, was transferred from the U.S. Air Force to UAF in August 2015.
Anybody who wants to participate and follow HAARP experiments should follow the official and unofficial announcements linked at the top of this page. There are two main ways to participate in the campaign: by listening to the radio transmissions from HAARP itself or by photographing artificial auroras created by HAARP. Amateur (Ham) radio operators can also use temporary ionosphere irregularities created by HAARP to open new propagation modes for their own transmissions.
A shortwave radio and knowledge of the time and frequency of the HAARP transmissions provides opportunities to “listen in” since the radio wave energy often (but not always) propagates very large distances, sometimes worldwide! Shortwave radios capable of receiving frequencies in the same range that HAARP can transmit, between approximately 2.7 and 10 MHz (2700 and 10,000 kHz) allow anyone to hear HAARP transmissions provided long-distance radio propagation conditions are sufficient and the radio is tuned to one of the frequencies where HAARP is transmitting. Ham radio operators also have an opportunity to reflect (or “bounce”) their own transmissions, typically in the HF, VHF or UHF bands, off ionosphere irregularities created above HAARP during high-power experiments. This creates propagation modes that would normally only be possible during certain space weather events such as aurora.
The video below shows one of the last scheduled HAARP transmissions from when it was still under the control of the US Air Force.
The WebSDR from the University of Twente, Netherlands is a wideband HF SDR that is accessible from all over the world via the internet. It was first activated in 2008 making it the very first WebSDR ever. The creator of the service Pieter-Tjerk de Boer PA3FWM has recently made available spectrum image archives which show the HF band conditions over the last two years.
The X axis represents the frequency and the Y axis is the time of day, starting at the top. Conventional wisdom about band behaviour can be easily confirmed by watching this video: the 60m, 49m and 41m bands are mostly active after dark, with the 60m and the 49m bands being generally busier during the winter months. The 31m band is most active around sunset, but carries on all night until a few hours after sunrise. The 25m band is active during sunrise and for a few hours afterwards, and around sunset during the winter months, but carries on all night during the summer. Peak activity on the 22m and 19m bands is also clustered bi-modally around the morning and the evening hours, though somewhat closer to the middle of the day than on the 31m and the 25m bands. The 16m band is mostly active during the daylight hours and the 13m band is quiet throughout the year except for the occasional ham contest.
Over on YouTube user Veryokay has uploaded a video that shows how he uses the HF direct sampling mode on one of our V3 RTL-SDR’s to receive WSPR signals. WSPR (pronounced “Whisper”) is short for Weak Signal Propagation Reporting, and is a HF ham mode typically run on very low power levels such as 1W. The data from WSPR reception can be used to determine how good or bad HF propagation is currently around the world as each WSPR message contains the callsign, 6-digit locator and the transmit power level used.
For the antenna Veryokay uses a simple random wire antenna directly connected to the SMA port of the V3 up on top of the roof of his apartment building. This gets him reception good enough to receive many WSPR signals. Then together with SDR#, VB Cable and the WSPR-X decoder software, signals can be received and decoded.
He has also uploaded a document detailing the instructions in text and image form at bit.ly/wspr-rtlsdr.
Over on the SDRplay blog and forums OH2BUA has been sharing how he has set up ‘propagation triggered recording’ by continuously monitoring JT65/JT9 signals with his SDRplay. The idea is that you leave the radio on receiving all night, and set it to automatically start recording IQ files if good propagation conditions occur as determined by the locations received from the JT65/JT9 signal. This may yield some interesting far off stations that can be listened to in the morning, whilst weeding out hours where nothing but commonplace local stations are heard. The software is a simple Windows batch file that works together to coordinate HDSDR and JTDX. It should work with any HF capable SDR.
JT65/JT9 are weak signal propagation HF modes (also known as WSJT modes) that can be decoded all around the world, even with very weak reception thanks to strong digital error correction. They can often be used to determine propagation conditions by determining where successfully decoded messages are being sent from.
I have made a set of scripts and other files which can be used to build a system which monitors JT65/JT9 (digital modes) amateur radio traffic on 160m/1.8MHz band, and if nice propagation to area you are interested in exists, a MW-BC-band recording is started. When the conditions fall off, the recording is stopped.
There is an attached zip-file containing all the necessary stuff. Sorry this is a windows thing – but easily portable also for linux. Create C:\bat\ and drop all there. Have a look, starting from README.
The default example is to start a MW-band I/Q-recording, if North American ham signals are heard – but it is fully modifiable according to your target when in comes to areas, bands, schedules etc.
The files are available as an attachment to the forum post.