My submission to Virtual Radio Challenge II

Sunday, September 28, 2014
Update (15/11/16): this article describes an older version of my portable SDR configuration. Jump to this post to see my current set-up.

A few days ago The SWLing Post published a challenge to their readers: given a budget of $1200, to put together the best possible shortwave radio listening set-up that can function completely off the grid in the Himalayas.

My solution is to fuse my two previous submissions to The Post - my response to the shortwave listening challenge for the remote Atlantic island of Tristan Da Cunha and my portable SDR design - and to add solar power.

FunCube Dongle Pro+ and Toshiba Encore 8" running SDR# in a London park
To recap, the tablet-based SDR set-up costs $643. My experiments with FunCube Dongle Pro+ and SDR# software have convinced me that this combination makes for one of the best shortwave listening experiences in its price range. Here are a few reasons why:

FunCube Dongle Pro+ is a sensitive SDR.
- SDR# has an excellent noise reduction algorithm that often turns laborious DXing into comfortable listening. It also has a robust synchronous detector, which, combined with its passband tuning and noise reduction algorithms can unbury almost any station from the surrounding co-channel interference.

However, given the remoteness of the location and the fact that there is no reliable electricity grid to speak of, we need a few extras:

Solar Power

You may recall that in my portable SDR solution there are two sets of batteries that need to be recharged:

- Toshiba's built in Lithium Ion battery (via its USB port)
- 4xAA batteries for the Gomadic 5V Power Pack (used for supplying extra power to the SDR)

First, let's get a compact, foldable solar panel:

1. Powerfilm F16-1200 20W foldable solar panel

I would go with Powerfilm F16-1200 20W foldable solar panel  (buy it here for $210.99). Disclaimer: although I've never used any of the PowerFilm products or accessories, I have read good reviews of them from other radio enthusiasts. When folded, this solar panel measures merely 27.9cm x 16.5 cm - slightly smaller than an A4 notepad. Once fully opened, however, it can deliver 20W of power (15.4V, 1.2A), enough to charge the Toshiba tablet and 4xAA rechargeable batteries simultaneously.

To charge the AA cells, I would go with the Powerfilm RA-3b - 12V Battery Charger Pack for AA and AAA (buy here for $54.41) and the Powerfilm RA-2 12V Female Power Port Adapter (already included with F16-1200).

2. RA-3b - 12V Battery Charger Pack for AA and AAA

3. RA-2 12V Female Power Port Adapter

Although we only need 4 AA batteries for the Gomadic USB Power Pack, it's always nice to have some spare ones, just in case. I would throw in a pack of 12 Panasonic Eneloop AA 2100 Cycle Ni-MH Pre-Charged Rechargeable Batteries for $26.95.

4. 12 Panasonic Eneloop Rechargeable Batteries
The spares can be used in the following ways:
- To power the backup portable shortwave radio
- To have another batch ready when the batteries insde the Gomadic USB Power Pack run out.
- Using Gomadic, to charge the tablet outside daylight hours, for more daytime listening.

Now onto charging the tablet itself. For this I would use the Powertraveller Spidermonkey 4-Port USB Charger Hub at $38.76. Again, I haven't used this product, but according to the specifications it can charge up to 4 USB devices and accepts input power between 5V and 30V. The reviews are largely positive, so it seems like a safe choice.

5. Powertraveller Spidermonkey 4-Port USB Charger Hub
To connect the Spidermonkey hub to the solar panel we'll need the Powerfilm RA-16 - 3ft. Extension Adapter with 4.75mm Barrel cable (available here for $9.98)

6. RA-16 - 3ft. Extension Adapter with 4.75mm Barrel
If we want to charge both the tablet and the AA batteries simultaneously, the  Powerfilm PP-7 - Multiple Device Charger Cable accessory will come in handy (here for $24.99)

7. PP-7 - Multiple Device Charger Cable

Antenna Extras

Living off the grid has the advantage of there being minimal man-made radio interference. For this reason we can use a larger antenna than in my original proposal. I suggest buying 40m of POLYS18 Copper-Clad Steel Antenna Wire from Universal Radio (the total comes to $31.44), cutting it halfway, and attaching each half to one of the two antenna terminals on the Wellbrook HF Balun, mentioned in my previous article, thus creating a dipole.

Of course, this makes for a rather powerful shortwave receiving antenna that can easily overload the radio. We can solve this problem by connecting the balun's feedline output to the antenna terminal on the Global AT-2000 Antenna Tuner, $85 via 25 feet of GadKo BNC Male Copper Stranded Center Conductor Cable , $16.90. We should then connect the radio terminal to the short feedline cable of the FunCube Dongle Pro+ SDR, with the ferrite chokes left in place. We will need 2 x BNC female to PL259 Adapters, $6.49, to connect the BNC cables to Global's PL259 female sockets.

8. Global AT-2000 Antenna Tuner
9. 2 x BNC female to PL259 Adapters
10. GadKo BNC Male Copper Stranded Center Conductor Cable

Finally, here's a simple schematic diagram of how the antenna parts should be wired together:

Connecting all the antenna bits together

Backup Radio

The challenge article mentions that a back-up radio would be desirable in the event of other equipment failing. I suggest Tecsun PL-310 ET, available for $48.79 from Amazon. It's a very similar radio to the excellent Tecsun PL-380 (they use the same Silicon Labs chipset), but it has one notable advantage: an external antenna input! It takes a 3.5mm jack plug, so we'll need a BNC Socket to Composite 3.5mm Male Jack Plug Adapter, $2.01.

11. Tecsun PL-310 ET
12. BNC Socket to Composite 3.5mm Male Jack Plug Adapter 

The subtotal for all of the above comes to $556.71. Adding on $643 for the tablet-based SDR solution brings the total to $1199.71, just 29 cents below the budget limit!