Guest Posts | The SWLing Post

The perfect radio for business travellers?

I travel regularly, or should I say commute between Europe and Asia, and have been on the lookout for a small receiver with good performance that would be easy to carry with me. I never travel without my laptop so an SDR would be the sensible thing to look for. A few weeks back the tiny FiFi SDR receiver caught my interest as I was browsing the website of Funkamateur http://www.box73.com/ the excellent German ham radio magazine. It looked promising as it had an impressive bank of filters covering all the way from LF to HF. Also, the front end is designed to emphasize sensitivity, so that it can work well with short wire antennas. It also had a built in sound card which would make interfacing to my computer a simple job.

The price was certainly right – $ 169. I ordered it, and it showed up in my mailbox a few days later. It is offered as a “kit” though in practice all that needs to be done is to solder a couple of connectors and sockets. All the surface SMD components are pre-soldered, and the rugged extruded case has die cut holes for the connectors and controls making the mechanical assembly very simple. The entire exercise took me about 20 minutes until the receiver was plugged in and powered up.

Since I use a Mac the choice of SDR software is a lot more restricted than that for Windows. I did however find free software called SDR Radio (http://dl2sdr.homepage.t-online.de/) developed by DL2SDR which does a great job of partnering with the FiFi and my Mac.

SDR Radio is still in development, so the UI can a bit rough at the edges at times. Also, configuring the Audio and MIDI settings on my Mac took a bit of work, but DL2SDR Sebastian was quick to reply to my mails requesting help when I got stuck.

So how does it all sound? While I am sure that there may be better performing SDR radios out there, what this little matchbox sized receiver does is simply amazing. Users running Windows will have access to much more sophisticated applications than the simple programs available for Mac and will be better able to compare this radio. However, it does an outstanding job of handling both AM broadcast as well as CW and SSB utility and Ham signals. While SDR Radio does not offer a lot of bells and whistles at present, the continuously variable bandwidth which can be dialled in to almost zero, and effective notch filter get the job done very well. In empirical testing and comparisons with the Palstar R30C, the FiFi easily outclassed the older analog radio (and the Palstar is no slouch, especially on the lower frequencies).

In summary, this is going to be the radio that I will be taking with me on all my travels from now on. It is tiny, ruggedly built, and has excellent RF performance, especially at lower frequencies.

Many thanks for your review, Anil!

The FiFi SDR does indeed sound like an ideal SDR for travel. Like you, I am usually limited by the SDR applications available on the Mac OS. While I use a Windows 7 PC at home, on the road, I travel with the MacBook Air (a superb laptop!).

Spread the radio love

One of the great things about the SWLing Post is that readers share their varied–and highly creative–methods of playing radio. A few weeks ago, SWLing Post reader, London Shortwave, shared his portable SDR set-up with us; he uses this outdoors to mitigate London’s heavy radio interference. Dennis Walter, president of Germany-based Bonito, commented, and later posted an alternative portable SDR solution using the Bonito RadioJet IF receiver.

Below, London Shortwave shares a guest post (also viewable on his blog) which describes in detail his design for his portable SDR around the FunCube Dongle Pro+ and an 8″ Windows tablet, and explains how effectively it works for him. This post includes recordings and a video; it’s an excellent tutorial:

DESIGNING A PORTABLE SDR SYSTEM

This article is a follow up to the submission I made to the SWLing Post a little while ago. In short, the idea was to combine the FunCube Dongle Pro+ USB-based software defined radio (SDR) with an 8″ Windows tablet running SDR# to have a portable, on-the-go SDR solution.

The original inspiration

Tablet radio interference

At the outset, I thought that all that was necessary was a tablet (I chose Toshiba Encore 8″), the FunCube dongle itself and just some antenna wire. This turned out to be a naive assumption because the tablet’s USB interface injected enormous amounts of radio frequency interference (RFI) into the SDR, making listening on some shortwave frequencies essentially impossible. Just to be sure that I wasn’t being plagued by a defect of my chosen tablet model, I tried out the same set-up on a Dell Venue 8, with identical results.

To deal with the issue of tablet-generated RFI, I bought a galvanic USB isolator, which, in essence, is a box that breaks the electrical connection between the USB dongle and the tablet’s USB interface while allowing USB data to pass through in both directions.

Heros Technology galvanic USB isolator

Additional power for the SDR

Connections

The isolator resolved the RFI issue completely, but created another problem altogether: the device specifications state that the isolator’s power output is restricted to 100mA at 5V. This is sufficient for USB devices that are self-powered but not for the FunCube dongle that draws all of its power from the USB port to which it is connected.

USB Y cable

One way to supply extra power to a USB device is to use a “Y-cable”. Such cables have one extra USB plug that can be attached to a source of additional power (for example, a USB power bank). This solution is commonly used to connect power-hungry items, such as large hard disks, to low-power, portable computing devices (laptops and tablets). Having bought this cable, my next step was to find/improvise a battery that meets the USB power specifications (5V, 500mA).

Yet more interference

My first thought was to use the mobile USB power bank that I use to charge my iPhone while on the go. After all, it already has a USB port and supplies power with the right voltage. Once again, my expectations were confounded and RFI reared its ugly head! The power bank radiates significant interference into the circuit because it uses a switching regulator to maintain steady voltage. Luckily, I came across Gomadic’s portable AA battery pack with regulated 5V output that emits way less interference than any of the other USB batteries I tried (my intermediate solution used 4 rechargeable AA batteries and a makeshift USB connector, and although this resulted in zero additional interference I decided that it’s not safe to supply the SDR with unregulated voltage that doesn’t match the rest of the circuit). I used the handy passthrough USB voltmeter I bought in Maplin to check that Gomadic’s nice-looking gadget does indeed give out 5V as advertised.

So, what can one do with the remaining RFI from the additional power supply? It turns out that it can be mitigated quite effectively by inserting a balun (item 10 on Figure 2) between the SDR and the antenna wire (item 12). The balun is connected to the SDR with a coaxial cable (the “feed line”, item 11). Additionally, ferrite choke rings (item 9) attached to the feed line help reduce this RFI further: winding the feed line through the choke rings several times is sufficient. However, neither the balun nor the chokes are effective enough to replace the USB isolator! It appears they only help with the noise generated by the power supply, which is relatively minor anyway.

Cost vs Portability

When SWLing Post published the details of my intermediate solution, Dennis Walter – one of the engineers behind Bonito RadioJet – popped up in the comments section and suggested that my setup is too tedious, as it involves lots of cables, and that his SDR is superior in terms of portability and the supplied software. While I haven’t had the chance to evaluate RadioJet, I pointed out that the cost of his radio is significantly higher than that of all of my components put together. I also mentioned that the free SDR# software I use is superb: it sounds excellent and offers a number of features that many software packages and conventional radios don’t have. So, having finalised my design, I thought that it might be time to tally up the cost and listen to the results.

Below is the full component list:

1) Toshiba Encore 8″ tablet $194

2) On The Go USB host cable for Toshiba’s micro USB connector: $7

3) Heros Technology USB Isolator: $125

4) USB Y cable with two males + 1 female plugs: $8

5) Gomadic Portable AA Battery Pack with regulated 5V output: $20

6) Gomadic female USB connector tip: $6

7) FunCube Dongle Pro+: $208

8) USB volt-meter (optional): $33

9) 2 ferrite choke rings: $10

10) Wellbrook HF Balun: $50

11) Feedline cables $7

12) 6 metres of thick copper antenna wire: $8

Adding up the prices of items 2 – 12 (and excluding the optional voltmeter) brings the total cost to $449 vs. Bonito RadioJet’s $689. For the price difference you can throw in the Toshiba tablet at $194 and still have some change, enough to buy a carrier bag and perhaps even a nice pair of headphones!

Figure 1. Radio components

Figure 2. Antenna components

In terms of portability, the entire setup fits nicely into an 11″ laptop carrier bag.

Figure 3. Packing the components into an 11″ carrier bag

Figure 4. Ready to go

Setting things up in the field is not particularly cumbersome, either:

Figure 5. Portable SDR setup in action in a local park

As for the results, listen to the below snippets and be the judge. The only thing I will say is that none of my other portable radios have ever given me this kind of performance, not even with the long wire antenna attached:

listen to ‘Channel Africa received in London, UK’ on Audioboo

listen to ‘Radio Nacional da Amazônia received in London, UK’ on Audioboo

listen to ‘Zanzibar Broadcasting Company received in London, UK’ on Audioboo

listen to ‘Radio Australia received in London, UK’ on Audioboo

And while we’re at it, here’s a demo video:

Portable SDR on Toshiba Encore 8″ Tablet from London Shortwave on Vimeo.

At one point I wanted to build an enclosure to house the FunCube dongle, the power supply and the USB isolator in a single tidy unit, but I no longer see the need. It’s easy to pack all of those items into the carrier bag and also they are all useful individually: the USB isolator can be paired with other SDRs, and I recently discovered a neat additional use for the Gomadic battery pack.

Well, that brings me to the end of this post. I hope my design will inspire you to come up with your own portable SDR system, and that you will share your results with me in the comments section. Happy listening!