New Year, new endeavours: ultra-portable shortwave spectrum captures in 2018

GPD Win, AirSpy HF+ and Tecsun PL-310ET

Hello and Happy 2018 to all the readers of the London Shortwave blog!

This post comes after a relatively long hiatus, as new work commitments starting last summer reduced the amount of time I could spend on shortwave radio listening. Longer working days and commute periods gradually encroached on the time slots that I had previously allocated for going to the park to record parts of the shortwave spectrum. (On the other hand, owing to continuously increasing urban RFI, my indoor reception conditions have deteriorated to the point of being essentially unsuitable for any serious radio listening).

However, just as I found myself under these new time constraints, my friend Thomas Witherspoon contacted me to tell me about his new initiative, The Spectrum Archive, and kindly invited me to become part of the team (which I gratefully accepted!). From the project website:

The Radio Spectrum Archive (RSA) allows listeners to experience radio history as it happened. It offers listeners the ability to tune through a radio band, listening not only to individual stations, but to all the stations in broad swathes of recordings, providing richly relevant radio context from the time. 

[...] 

The Spectrum Archive team actively creates new spectrum recordings and maintains existing spectrum recordings for current and future use by, among others, historians and researchers.

The opportunity to contribute to this unique project renewed the impetus for me to find a way to create outdoor shortwave spectrum captures on the go without having to make return trips home to drop off my relatively bulky recording equipment.

PocketCHIP and FunCube Dongle Pro+ (September 2017)

My first attempt at this was to use the PocketCHIP portable computer and the FunCube Dongle Pro+, together with the Sony AN LP-1 foldable active loop antenna:

The idea was to have a spectrum capture set-up that could fit into the side pocket of my laptop bag and be quickly deployed in any open space.

PocketCHIP runs Linux, for which there are plenty of SDR applications, however, because of CHIP's limited CPU capabilities it is difficult to get any of them to run glitch-free. As a result, it's possible to inspect the spectrum visually prior to starting the recording but it's impossible to do both at the same time and there is currently no way of monitoring the audio while the recording is underway.

On Linux, FunCube Dongle Pro+ can be accessed without any SDR application running in the background (a big advantage given PocketCHIP's limitations): the dongle uses the sound card I/O interface and a simple audio recording utility such as ecasound can be employed to record the I/Q data stream to disk. However, the main drawback of this dongle is that it can only capture 192 kHz at a time, making it impossible to record an entire shortwave band in one go. On the other hand, PocketCHIP's battery life is around five to six hours, far longer than that of any of my laptops or tablets.

GPD Win and AirSpy HF+ (November 2017)

In November I received a sample of AirSpy HF+ — a very sensitive, compact SDR, capable of recording an entire shortwave band in one go. I used it to form an alternative ultra-portable capture set-up: the antenna is still the Sony AN LP-1 compact loop but the PocketCHIP is replaced with a similarly-sized GPD Win: a fully functional 5-inch (!) Intel PC running Windows 10:

AirSpy HF+ is tightly integrated with SDR# — a Windows application — which ended up being the main rationale for getting one of the most portable Windows computers out there and putting it to the test. After a bit of tweaking and experimentation (which I'll describe in detail in one of my next posts) I managed to get it to work. GPD Win's CPU is capable of running SDR# without any problems, its battery lasts around 4 hours when recording the spectrum and the Sony loop antenna proved to be very sensitive indeed:

The above two recordings were made with the GPD Win / AirSpy HF+ / Sony loop combination on Christmas eve in a London park, and the quality easily rivals that of the captures I have made with my regular outdoor set-up under similar propagation conditions.

I hope the greater portability will allow me to continue making outdoor spectrum recordings under increased time pressure. Thanks for reading and wishing you all a great year with lots of interesting radio catches!

GPD Win, AirSpy HF+, Bonito GI300 isolator and the Sony AN LP-1 loop antenna preamp out in the field