Tag Archives: SDR Spectrum Recordings

Visualising shortwave band activity throughout the year

This article originally appeared on the London Shortwave blog.

24-hour shortwave spectrum image, showing activity for a single day in the first week of February 2017 (©PA3FWM, Twente WebSDR).

As many of my readers and followers will already know, these days I mostly enjoy listening to shortwave radio via the outdoor spectrum captures I make in my local park. Although I have built a system that helps me deal with urban radio interference at home, some of the weaker signals still can’t make it through the indoor noise. Since I have a limited amount of time for making outdoor trips, capturing entire portions of the spectrum allows me to record a lot of shortwave signals simultaneously, which I can then explore individually at a later time. However, these trips still need to be carefully planned because the time of the day and the time of the year both affect long-distance signal propagation, and do so differently depending on the frequency range. For example, signals on the 16 meter band are usually at their strongest during the daylight hours, whereas the 31 meter band is at its busiest around sunrise and sunset. Because my current portable recording set-up allows me to capture only 10% (3 MHz) of the shortwave spectrum at any one time, I decided to carry out a systematic exploration of activity on the shortwave bands to help me time my outings so as to capture as many signals as possible during each trip.

Capturing the shortwave spectrum out in the field with a portable SDR set-up.

Luckily, I didn’t need to make any of my own measurements for this. For over a year, the wide-band WebSDR at the University of Twente has allowed its users to see what the shortwave spectrum has looked like over the past 24 hours in a single image. More recently, however, the creator of the service, Pieter-Tjerk de Boer PA3FWM, has opened up his spectrum image archives, so it is now possible to see the past conditions of the bands on any single day in the last two years. Intrigued by how band activity changes depending on the time of the year, I created a timelapse animation of these images by taking two from each calendar week and lining them up in sequence. With Pieter-Tjerk’s kind permission, I share this animation below.

First, a really fast version to illustrate the broad effects the time of the year has on peak activity times across the bands:


 Click here to view on YouTube

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.

It almost seems as though someone positioned in the middle of the image’s right edge (corresponding to noon UTC) is shining two flashlight beams on the bands in a V-shaped pattern, and is changing the angle of this pattern depending on the time of the year: wider in the summer and narrower in winter. Here’s a slower version of the animation that shows some finer week-on-week changes:


 Click here to view on YouTube

Thanks to this data being made freely available, visualising and understanding these dynamics will help me schedule my spectrum capture outings in the weeks and months ahead.

Propagation-Triggered Spectrum Recording

Many thanks to Jon Hudon of SDRplay who shared the following on the SDRplay Facebook page:

One of the SDRplay user community, Jukka, has started an interesting discussion on what he has called ‘propagation-triggered recording’ – he outlines the concept, and what he is doing, on our forum – see http://www.sdrplay.com/community/viewtopic.php?f=9&t=1839

The idea is that you monitor signals to determine if conditions are particularly good and can thereby trigger an I/Q recording of a whole band during that particular propagation high point -Jukka welcomes more comments on this idea.

Many thanks, Jon. I would certainly be a fan of this as so many times I’ve missed fantastic band openings while travelling. It would be nothing short of brilliant to come home to automatic SDR spectrum recordings taken during prime propagation. At the moment, propagation is so dismal, rare openings are worth recording!

As Jon points out above, check out the SDRplay forum for more details.

Capturing spectrum and logging band openings last night

My 31 meter band spectrum display last night. Strong signals across the board.

Waterfall display of the 31 meter band last night.

Last night, band conditions were superb above 7 MHz. Both the 31 and 25 meter bands seemed crowded with stations; for a moment, it felt like a true solar peak.

This morning, solar flares have dampened down the excitement but I imagine conditions could favorably change at times this weekend, so stay tuned!

I recorded the entire 25M band for a couple of hours yesterday evening and a large portion of the 31 meter band throughout the night. Fortunately, I had just invested in another Western Digital Caviar Green 3 TB SATA drive, so there was ample space to make these (very) large recordings. I think this brings my overall spectrum storage up to 12 TB!?!

I love the fact that these SDR band captures will make for good listening sometime this winter when the sun isn’t being so cooperative. I liken it to radio time travel, but I believe David Goren (of shortwaveology.net) said it best in a comment he posted in “Confessions of an SDRaholic: when 4.5 terabytes is not enough“:

“My approach to recording SDR band captures is like assembling a collection of fine wines. I tend to record captures when there are unusual propagational openings…and while recording a whole swath of frequencies for an hour or so you can still tune around and make discoveries and even record them singly.. And then once the capture is done, you have it as long as you want to keep it.. So, on a static-y summers day I can go to the shelf and pull down “Ye Olde Auroral MW Opening 10/15/11? or “Hot Bolivian evening on 60 meters.” and I can make discoveries to my heart’s content. Since I can listen to an hour’s worth of each frequency it will take a long time to exhaust the potential of any particular capture, esp. with the ability to refilter and change. multiple parameters of reception.”

See? (I tell my wife) I’m simply building my collection of fine wines!

Below, you’ll find some of the stations I logged last night (actually, this morning in UTC).

Logs:

31 meter band beginning 00:00 UTC, 25 OCT 2014

  • 9410 BBC English Nakhon Sawan
  • 9420 ERT Open/VOG Greek
  • 9455 China National Radio 1 Chinese
  • 9470 AIR National Channel Hindi/English (vy wk)
  • 9475 WTWW English
  • 9510 China Radio International Russian
  • 9520 PBS Nei Menggu Chinese AND Radio Romania International Romanian
  • 9565 Radio Tupi/Super Radio Deus e Amor Portuguese (QRM from CRI 9570)
  • 9570 China Radio International English
  • 9586 Super Radio Deus e Amor Portuguese
  • 9590 China Radio International Spanish
  • 9630 Radio Aparecida Portuguese
  • 9645 Radio Bandeirantes Portuguese
  • 9660 Radio Taiwan International Chinese
  • 9665 China National Radio 5 Chinese or possibly KCBS Pyongyang Korean
  • 9690 All India Radio English
  • 9700 Radio Romania International English
  • 9705 All India Radio English
  • 9710 China Radio International Portuguese
  • 9730 Adventist World Radio Manumanaw Karen or possibly 9730 Myanmar Radio Burmese
  • 9740 BBC English (vy weak)
  • 9800 China Radio International Spanish
  • 9810 Radio Havana Cuba Spanish
  • 9820 Radio 9 de Julho Portuguese
  • 9855 Voice of America Tibetan
  • 9860 Voice of Islamic Rep. of Iran Spanish
  • 9870 AIR New Delhi Hindi
  • 9880 Voice of America Chinese (vy weak)
  • 9935 ERT Open, VOG Greek
  • 9965 Radio Cairo Arabic
  • 10000 WWV Ft. Collins

25 meter band beginning  0100 UTC, 25 OCT 2014

  • 11520 EWTN (WEWN) English
  • 11580 SOH Xi Wang Zhi Sheng Chinese/Cantonese
  • 11590 Radio Japan Hindi (vy weak)
  • 11620 China National Radio 5 Chinese
  • 11640 Radio Free Asia Uyghur
  • 11650 China Radio International Chinese
  • 11670 Radio Havana Cuba Spanish
  • 11695 Radio Free Asia Tibetan
  • 11710.7 Radio Cairo Spanish (transmitter noise)
  • 11760 Radio Havana Cuba Spanish
  • 11780 Radio Nacional da Brasilia Portuguese
  • 11825 Bro Stair
  • 11840 Radio Havana Cuba Spanish
  • 11855 Radio Aparecida Portuguese
  • 11870 EWTN (WEWN) Spanish
  • 11905 Sri Lanka BC English/Hindi
  • 11955 Radio Romania International French
  • 12020 VoA Deewa Radio Pashto
  • 12025 UNID
  • 12070 Radio Cairo Spanish (jammed or transmitter noise?)
  • 12105 WTWW Spanish

Confessions of an SDRaholic: when 4.5 terabytes is not enough

WinRadioExcaliburFullScreen Alas, ever since I started using Software Defined Receivers (SDRs) last year, I’ve found that I fill up hard drives faster than I can buy them. As you may have noted, I like to make spectrum recordings–especially during the night-time hours, as I slumber. The following morning, upon waking, I’ll “tune” through, say, the 31 meter band as if it were live. What makes it even more amazing for me, is that I can fast-forward through time and scan for DX stations even more quickly.  Great fun–highly addictive.  And did I say, space-consuming?

On my WinRadio Excalibur, I find that I use about 4 gigabytes of hard drive space for a one-hour-long spectrum recording, 100 kHz wide. Of course, if I were to record a 2,000 kHz (2 MHz) chunk of spectrum, it would chew through 4 GB in, roughly, 3.5 minutes.

Fortunately, I rarely ever record spectrum that wide. I find that the maximum width I ever record is 1.25 MHz, which I reserve for occasions once in a blue moon. Most of the time, I stick to 100 kHz-160 kHz widths.

After I record a chunk of spectrum, I usually listen to it, create an AF recording of anything of interest, then delete it from my drive. You’d think this would effectively keep my hard drive cleared out, ready to receive the next installment? Not so. Well, at least, not in my undisciplined SDR beginnings.

The flaw in my logic

Quite often, I make spectrum recordings while traveling, and do so remotely (using TeamViewer to control my PC). In the past eight months, I’ve done a lot of traveling. When I return from a trip, I find that I’ve often amassed a sizable collection of spectrum recordings. Upon returning from travel I also find (not surprisingly) that I’m typically busier than normal, catching up with email, phone calls, and delayed appointments. Thus, I never quite get around to reviewing–and therefore deleting–these files. Most of the spectrum recordings taking up space on my internal drives are those I’ve recorded remotely.

Last year, I thought I’d solve the space problem on my ailing laptop by purchasing a dedicated tower PC (Core i5) maxed-out with RAM and with a 1TB internal (7200 RPM) hard drive. This particular Gateway PC also has a bay that accepts cheap internal SATA drives; I simply insert an internal SATA hard drive in the ejectable bay, load the drivers, and it’s good to go. When I purchased an additional 2 TB SATA drive for spectrum recordings, I thought I would be set for years to come…Ah, how the mighty crumble…

As I write this today, I find I only have a total of 350 GB available on my PC. I’ve also filled an entire 1.5 TB external hard drive with recordings I plan to archive and share with a fellow SWLer.

The Tandy Color Computer 2 (or, "CoCo 2") was my first personal computer. (Image: Wikimedia Commons)

The Tandy Color Computer 2 (“CoCo 2”) was my first personal computer. (Image: Wikimedia Commons)

My, how times have changed

Reverse to the 1980s:  When I was ten years old, I thought my Tandy Color Computer 2 was the best thing since sliced bread.  Its 16 kB was surely plenty of memory for whatever I wanted to do, and the cassette tapes I used as a form of external hard drive gave me the certainty of a virtually limitless supply of memory.

Today, I doubt I could make an intelligible MP3 recording, even with aggressive compression, that would fit a 16 kB file size.

Facing the truth

The frank fact is that I’ve gotten much better at managing hard drive space, now that I’ve been doing spectrum recordings for more than a year. I shouldn’t need to buy additional hard drive space unless it’s specifically for archiving/sharing purposes. I just need to regularly face the music (or static)–dig through spectrum recordings made last year, and delete those I no longer need.

How do I manage space now? Here are my tricks for staying on the wagon, and saving both space and time:

  • Use the minimum amount of bandwidth possible while making recordings
  • If possible, have your SDR parse files into 2GB chunks. This makes it easier to delete sections of recording that are no longer needed without having to delete the entire recording. Happily, the WinRadio Excaliber allows for this.
  • Each time you create a new spectrum recording, have it saved into a specific directory with a label that will help you identify the contents.  For example, “Saturday Night Pirates” or “31 M Tues AM.”
  • Use Notepad or any simple text application and create a log sheet for the spectrum recording; make notes, then save it in the same directory as your spectrum recording.
  • When saving MP3/WAV files, use a standard file-naming convention to help you quickly ID a recording (you’ll notice all of my recordings do this). Mine follow this pattern: “StationName-Fequency-Date-StartingTimeInUTC.mp3” –e.g., “RadioAustralia-9580kHZ-05Feb13-1000Z.mp3”
  • Delete unwanted spectrum recordings as soon as you decide they are not worth keeping. If you wait a few days, you may forget that they’re okay to delete.
  • I also use my Bonito RadioJet for narrow IF recordings (of, say, one station).  It allows me to adjust filters and “tune,” but takes very little hard drive space. The same can be achieved by narrowing your SDR spectrum width to 20-48 kHz.

Are you an avid shortwave/medium wave audio archivist (aka, audio addict)?  What are your tricks of the trade?  Please comment!

Test a professional SDR from the comfort of your home–free!

Though I’ve not yet achieved particularly advanced age, my history in radio certainly started with the analog. The vintage Zenith Transoceanic my great-aunt gave me when I was eight was a wonder to tune, and its ability to extract signals from across the planet captivated me. But there was a certain amount of guesswork in the tuning process.  So, when I purchased my first digital portable in 1990, it seemed revolutionary:  in a snap, I could punch in a frequency, and there I was (virtually speaking). No guessing required.

Front and back of the SSB LAN-SDR software-defined receiver

Front and back of the SSB LAN-SDR software-defined receiver

The next step in receiver evolution was, of course, Software-Defined Radios–those little boxes that you hook up to your computer that allow you incredible tuning flexibility and which permit amazing receiver performance.

So, you’ve never tried an SDR–? I know a fix for that.

In the course of an email conversation with Willi Paßmann, SDR support for SSB-Electronic, I learned that–simply by downloading a couple of files from their website–you can “test-drive” their high-end SSB LAN-SDR.

First, a brief primer…

Some SDRs–like the SSB LAN-SDR–actually allow you to record and to play back HF spectrum segments.

In a basic example: if I want to record pirate radio stations one evening, but am not sure where they might pop up on the spectrum, I can set my SDR to record, say, an 80 kHz swatch of bandwidth from 6,915 to 6,995 kHz, from, for example, 9:00 pm to midnight.

Later, I can play back and listen to the recording, with full demodulation and tuning capabilities.  In other words, during playback, I can literally tune around in the spectrum, using all/any receiver functions of my SDR. It is as though I am listening and tuning, live, in real time, though it may be many hours or days later.

Those of you with SDRs will not be surprised by this remarkable feature, as most likely, you’ve already experimented with this incredible time-bending functionality.

Now, back to SSB-Electronic, and how to test-drive their LAN-SDR receiver.  It’s easy, actually:

  1. You download the software that runs the LAN-SDR
  2. You download one (or both) available spectrum recordings

Once you install their software and import the recording, you can literally tune through and use all of the receiver’s features within the spectrum recording. You can listen to the noise floor, test the notch, adjustable filters, DSP, tuning rates–literally experience all the receiver functions in this process.

In my humble opinion, this is perhaps the most convenient and enjoyable way to try out a receiver.

Hopefully, other SDR manufacturers will follow SSB-Electronic’s lead and make their control software and spectrum recodings available online for download and testing.

Happy test-driving!