Over on the Reddit discussion boards user gat3way has posted about his newly released software project called swscan. Swscan is a Linux console based program that can be used to scan and listen to shortwave broadcast stations. It has a built in database of shortwave station frequencies as well as their broadcast schedules and it will even show you the stations power level and distance you are from the transmitter. Swscan is based on GNU Radio 3.7, so you will need to have that installed first.
As shortwave stations exist at frequencies below the normal tuning range of the RTL-SDR, you will need an upconverter or be using the latest R820T experimental driver which can tune down to around 1 MHz.
Over on the Osmocom mailing list, Oliver Jowett an RTL-SDR experimenter has posted about his new experimental driver for the R820T RTL-SDR which extends the tunable range down to around 13 and up to 1864 MHz (previously 24 – 1766 MHz). Oliver writes
You can get these changes from https://github.com/mutability/rtl-sdr/ (you’ll need to build from source yourself). There should be no application changes needed, just tune as normal. (gqrx needs the “no limits” option turned on) These changes work by limiting the tuner to a range of frequencies that it can reliably tune to, then allowing tuning beyond those bounds by making the 2832’s downconverter do the final bit of tuning. This can add up to 14.4MHz to each end of the range. Also, the tuner is switched to low-side mixing at the top of the range which gives a bit more range there. The practical range is limited by the width of the IF filter and aliasing effects at the extreme edges of the downconverter’s range. I’ve been able to pick up broadcast AM and amateur CW/SSB down to around 15.5MHz without too much trouble. I’d be interested to know how this works for others. Also.. these changes are likely to have broken offset tuning, direct sampling mods, and tuners other than the R820T, as it touches all those areas but I only have an unmodified R820T to test against. If you have different hardware and are willing to spend some time testing then please let me know. I expect that the range of the other tuners can be extended in the same way with not much trouble.
Over on the Reddit RTL-SDR discussion board there has been talk about this patch. Most users are reporting that it works well down to around 15 MHz, but some people are reporting that they have been able to receive signals down to around 4 MHz. Testers also report that this modified driver works much better than the no-hardware direct sampling mod patch released a few months ago.
A new HF upconverter designed for the RTL-SDR has gone up on ttrftech’s Japanese language blog (use Google Translate). The upconverter is called the ‘SC-HFCONV-100’ and comes with 100 MHz oscillator, SMA connectors, USB mini-B power.
A few months ago we posted about a Chinese individual (BA5SBA) who had begun selling RTL-SDR dongle kits for receiving HF frequencies. Back then it wasn’t entirely clear what these kits were or where they came from. Now over on Reddit, poster SidJenkins has bought one of these kits and assembled it. He has uploaded images of the construction which can be found here and the Reddit discussion can be found here. The kit is essentially an RTL-SDR extension PCB board that aids in building a direct sampling RTL-SDR with good performance by including filters and impedance matching.
SidJenkins notes that the kit came with no instructions, so he used this thread in Chinese (use Google translate) to help put the kit together.
Over on YouTube user crookedninja5 has uploaded a video showing what he calls the “Easy HF dongle mod”. The mod involves soldering a wire from Pin 1 on the RTL2832U chip to the static protection diode near the antenna input. At the same time he also uses the modified RTL-SDR dll file for SDR# which enables the “no hardware mod” direct sampling mode.
Using this mod he is able to get decent coverage of 0 – 14.4 MHz.
Mile also uses a band pass filter and notch filter to improve the dynamic range of the RTL-SDR. Additionally, in the video he shows a comparison between a large delta loop antenna and the mini-whip active antenna which shows better performance by the mini-whip.
RTL-SDR on VLF (ALPHA Russian Long Range Navigation System receiving in Macedonia with MiniWhip)
Over on YouTube user Alex swl has uploaded a video showing his reception of a Very Low Frequency (VLF) radio signal using a laptop running SDRSharp and a Chirio Mini Whip antenna connected directly to the laptop’s sound card input.
Every year on Alexanderson Day (this year on 29/06/2014) and some other days the Varberg VLF Radio Station in Sweden transmits a morse code message using a 1.9 km (1.2 mile) horizontal wire antenna at 17.2 kHz with callsign SAQ. Because the transmission frequency is so low, a standard PC soundcard can be used to directly receive the signal.
Alex swl was able to receive this signal in Italy.
In previous posts we have featuredMartyKN0CK’spopularmodified RTL-SDR dongles which have either a miniature built in high quality HF upconverter with amplifier and filter, or an amplified and filtered direct sampling modification applied to them. With these modified dongles you can receive the HF frequencies from 0.5 MHz to 54 MHz. These kits were previously available for sale on a webstore, however that store has since closed down.
Fortunately, Marty’s modified RTL-SDR dongles are still available at http://www.kn0ck.com/HF_SDR/. The HF upconverting dongle can be bought for $75 and the direct sampling dongle at $60. The store page also shows example videos of the performance you can expect.
KN0CK HF Upconverting RTL-SDR ModificationKN0CK HF DIrect Sampling RTL-SDR Modification
