Tag Archives: SDR Spectrum Recordings

Don shares spectrum recordings from northern Peru

Many thanks to SWLing Post contributor, Don Moore, who writes:

I’ve been traveling through northern Peru and I’ve made some SDR recordings along the way – medium wave, long wave, and some shortwave meter bands. I hope to eventually get through them all!

I have also uploaded some recordings to a shared Google drive so that other DXers can hear what the bands sound like in northeastern Peru, on the edge of the Amazon jungle. Maybe some of the blog readers would be interested in this. You will need the below link to see the SDR files and an explanatory document. I plan to add a few more once I get another hotel with a good Internet connection again.

Click here to download.

Fantastic, Don!  Thank you for sharing your spectrum recordings!

Post readers: If you don’t already have HDSDR installed on your PC, you’ll need to grab it here. HDSDR is free and can playback these spectrum recordings. Once installed, simply press the “play” button on the HDSDR console and point HDSDR to the downloaded spectrum file. You’ll be tuning through Peruvian spectrum in no time!

Also, check out Don Moore’s excellent blog: http://www.donmooredxer.com 

Shortwave Archives, Spectrum Archives and the Radio Preservation Task Force meeting

This week, I’m looking forward to participating in the three day Radio Preservation Task Force meeting in Washington, DC.

The Radio Preservation Task Force (RPTF), a project of the National Recording Preservation Board of the Library of Congress, will be held on November 2nd, 3rd, and 4th, 2017 at the Library of Congress, Woodrow Wilson International Center for Scholars, and the University of Maryland.

I’ve been invited to serve on the RPTF Material & Digital Curation panel where I’ll have an opportunity to talk about our work with the Shortwave Radio Audio Archive and a new project I’ve been working on: the Radio Spectrum Archive.

The Radio Spectrum Archive

For several years, I’ve been championing the concept of archiving radio spectrum recordings.

As many of you know, through the use of software defined radios (SDRs), we can record not just one individual broadcast from one radio station at a time, but we can record an entire broadcast band, all at once. Each recording can easily contain dozens of stations broadcasting simultaneously. Later, via an SDR app, recordings can be tuned and listened to as if they were live. We believe spectrum recordings will be valuable material for the future historian, anthropologist, enthusiast, etc.

Screen shot of the RSA homepage.

I’ve published a new website for the Radio Spectrum Archive and I encourage you to check it out as it outlines our mission, goals and challenges. I also include a video demonstration using a spectrum recording from 1986 (originally recorded on a HiFi VCR!).

Note that the website is a work in progress, there are still sections to add including bios of our spectrum archive team.

Click here to check out the Radio Spectrum Archive website.

Though I didn’t mention this in my Patreon campaign post earlier this week, the Radio Spectrum Archive is yet another important radio project you are supporting with your pledge. This week, for example, extra funds help me with travel expenses associated with the RPTF conference (many thanks to a kind friend who is hosting me at his home for four nights, saving me several hundred dollars!).

If you have the means and would like to support the SWLing Post, the Shortwave Radio Index, the Shortwave Radio Audio Archive, and the Radio Spectrum Archive please use the link/button below to become a Patron. If you’d like more details or support options, check out this recent post.

Become a Patron!

And to all of you who have supported us through Patreon and with one time gifts: thank you, thank you, thank you!

If you’re not in a position to become a patron or coffee fund supporter, no worries! Just enjoy our radio sites and resources!

One more note: Due to travels and a heavy workload over the next couple of weeks, please allow extra time for replies to correspondence and comments. Thank you so much!

SDR Spectrum to Radio: Can someone please make this device?

The venerable RF switch box from the 1970s/80s allowed game consoles and computers to use analog TVs as monitors.

As I’ve mentioned in the past, I actively record and index radio spectrum recordings via my various software defined receivers. Indeed, I have at least 50 TB of SDR spectrum recordings at the moment–and that number is growing!

I was just chatting with SWLing Post contributor, Mark Fahey, and a familiar topic came up: the idea of an RF switch box for radios.

The concept is a piece of hardware that re-modulates–converts digital spectrum data from a digital storage device back to analog RF– and injects a signal into a real tabletop radio.

As Mark described:

“This is just like early computers and Atari-like games consoles did to allow the “computer” to display on a lounge room TV. The games console tricked the TV into thinking it was tuned to a TV station on “Channel 1 (or whatever the console outputted the video to).”

Radio time travel machine!

How cool would it be to take a spectrum recording from 2008, play it through your Hallicrafters SX-100, Kenwood R-1000 or Alinco DX-R8T, and tune through the 31 meter band? You’d receive Radio Australia, Radio Bulgaria, Radio Netherlands Worldwide, Radio Canada International, Voice of Russia and many other broadcasters that are no longer on the air. Indeed, there’s a strong possibility you might uncover DX you didn’t catch when the recording was first made.

I’m enough of a radio geek to know that I would thoroughly enjoy travelling back in time once in a while with a classic radio.

Additionally, this device would make it much easier for museums to create kiosks where visitors could tune through recordings of, say, important events in history.

Can it be done?

I know the technology is out there.  In fact, if you’ve ever been to a large hamfest where Icom, Yaesu or Kenwood have a number of their transceivers “on the air”–so customers can try out transceiver features–they are using a device called a “radio time machine.”

Icom uses recorded IF instead of live antenna input so customers can experience “contest conditions” while evaluating a radio.

The Radio Time Machine injects recorded analog RF, from a HiFi VCR, into the antenna ports of a vendor’s various transceivers. The recordings are typically of a ham radio band during a contest–that way, the customer can get a sense of how well the rig would perform under crowded band conditions.

These devices have limitations: while their bandwidth is ample to tune through the CW or phone portion of a ham band, it’s much too narrow for most broadcast bands. They’re also fed the recording from an analog HiFi VCR.

The device Mark and I dream of would convert digital spectrum files–from a WinRadio, Perseus, Elad, SDRplay, Airspy or other SDR–into analog RF any radio with an external antenna port could tune.

SWLing Post readers: you’re a diverse and knowledgeable community–please comment if you know what it would take to develop such a device and how it could be done. Is this a dream or could it become reality?

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.