Portable SDR update

Update (15/11/16): this article describes my old portable SDR configuration. Jump to this post to see my current set-up.

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This is a quick entry describing an update to my portable SDR setup. Readers may remember that my previous configuration suffered from the tablet's radio interference leaking into the FunCube Dongle Pro+ SDR. I solved the problem by using a galvanic USB isolator and a separate portable USB power supply for the dongle. When I posted this configuration on SWLing.com in August, Alexander DL4NO advised me that it's possible to get rid of the USB isolator. Because my balun has two terminals, he said, I can use it to make a dipole antenna (an antenna with two wires) that balances the radio current before it gets passed down into the SDR dongle, which ought to prevent tablet interference from getting into the antenna system.

At the time I wasn't sure this would work. His other suggestion — using a ferrite ring choke on the antenna feedline cable — didn't do much to suppress the tablet noise, which made me assume that it was FunCube Dongle's design that was at fault, and that the noise was getting in from the USB end and not via the antenna.

Wellbrook UMB130 balun

However, when I finally tried out Alexander's suggestion, I could not believe what a drastic effect the addition of the second wire has: as soon as I connect it to the balun, the noise disappears, even with the USB isolator "out of the loop". This simplifies my portable SDR configuration substantially. Below is a demo video:

There is no sound here because I was listening to Radio Australia's 12065 kHz signal using a pair of Bluetooth headphones. Note the low noise floor and the absence of any interference on the spectrum. This has a substantial impact on the overall cost:

1) On The Go USB host cable for Toshiba's micro USB connector: $7
2) FunCube Dongle Pro+: $186
3) Wellbrook HF Balun: $60
4) Feedline cables $7
5) 12 metres of thick copper antenna wire: $16

The total without the tablet comes to $276, and if you buy an HP Stream 7, you only need to add $90 more. A complete on-the-go SDR solution for $366 doesn't sound too bad, does it? Many thanks to DL4NO for making my set-up that much more portable!