Friday, August 10, 2012

Take Your SDR To The Beach

Getting away from man-made noise has become increasingly important for DX-ers - and increasingly difficult. Going to the seaside or into the mountains can provide excellent opportunities for DX. But you need power! A laptop can last a night if one brings along an extra battery. However, feeding a 5V SDR from the laptop will either not work at all (too much current load), or it will drain the laptop's battery rather fast.

Battery packs have been around for a while. Some of them are quite powerful. After a quick search on Ebay I ordered a 11200 mAh battery pack which has two 5V outputs, rated at 1A and 2.1A. It came with a variety of adapters and connectors so one should have no problems to charge any mobile phone on the market today.

No, you can't power an R-390A with it... 
Left and right: 5V outputs. Middle above: DC input. Middle below: LED lamp

But the battery pack can do more than to give extra juice to demanding smartphones. The one I bought can power two SDRs! The Perseus draws around 750 mA while the Afedri has a modest 390 mA demand. At least in theory, this battery pack will power the Perseus almost 15 hours, and the Afedri almost 29 hours.

I don't know how much current is necessary to run the NetSDR - probably a bit more than the Perseus but less than 1A since I could feed all three of my 5V SDRs from the 1A output.

Before connecting the battery pack to my SDRs I checked the voltage of the DC outputs. I was somewhat surprised to see that they weren't quite the same. The 2.1A output measured 4.95V which is very good, while the 1A output measured 5.35V. That's a bit on the high side. Although all three SDRs worked with 5.35V when I tested them, I have decided not to push my luck. I'll stick to the 2.1A, 4.95V output.

Otherwise, the battery pack is a nice looking, small and light device.  The enclosure had FCC and CE logos on it, hopefully for a reason, and the price was USD 40 including air mail shipping from China. And they've even built a LED torch light into it. So you can search for the car keys you dropped when you erected the antenna.

Update Aug 11:
I let the battery pack feed the Perseus for most of yesterday, until only the last of the indicator LEDs were lit. How much juice was left I don't know. I was expecting (or fearing) that voltage would drop as the battery drained. However, the voltage reading of the 1A output was identical (4.95V) to the voltage when the battery was fully charged. So apparently, the battery is able to keep voltage stable for a very long time.

Thank you Takashi Kuroda for making me aware of these devices.


NHP said...

Please tell us more Bjarne. I haven't been able to find this with a quick search on Ebay in North America.

Does it come with its own charger?


Anonymous said...

Search for Yoobao?
73 Johan L SWE

Bjarne Mjelde said...

The one I bought is here:

Anonymous said...

Very interesting and many thanks for the advice, Bjarne! I did a quick scan on eBay and there's an ocean of these USB Battery packs, up to 15000 mAh.

By the way, how do you charge the battery pack? Does it come with an own charger or is it charged via USB from the PC?

73 de HR in Vardø

Bjarne Mjelde said...

Hans, mine came with a dual-voltage charger, alas with US AC connectors so you will need an adapter. You can charge it from a PC's USB port (slow), or basically use any mobile phone charger with a USB interface. I'm using an old Sony Ericsson charger.

4nradio said...
This comment has been removed by the author.
Guy Atkins said...

Hi Bjarne,

Despite the FCC/CE logos, have you noticed any noise (rfi) coming from this USB battery pack?

73, Guy

Bjarne Mjelde said...

Guy, a battery should not emit any RFI - unless of course it's being charged, in which case it's the charger. No noise detected from the battery pack.

Guy Atkins said...

Good to learn there is no noise coming from the battery pack!

The reason I asked is that these packs typically use a 3.7V total capacity of the internal cells, and therefore need a DC-to-DC converter to bump the voltage to the 5 volt USB standard for output.

These DC to DC converters can be like switching power supplies-- noisy! Some of your readers may remember the discussions about the NRD-525 and 535 series of receivers in the 1990s; the fluorescent display's DC-to-DC converter was identified as the source of the RFI coming from the radio's front panel.

Bjarne Mjelde said...

Aha...well that I didn't know. I'll be a bit more observant the next time I test the device, however I don't expect to have to change my mind ;-)

Anonymous said...

Bought it! But I got mine for $27.99 and free shiping from this seller:

Dave Aichelman - Dewey,AZ said...

iSound makes a 16amp USB power pack also that has 5 USB ports and an assortment of charging cables. You would have to get a Perseus 2.5mm to USB cable separately from Amazon/Ebay for about $3 US. It appears to be a 12V power pack regulated down to 5V. There is no power limit on the 5 ports as it is for multiple IPAD's. It does generate some noise that can be eliminated by moving the battery pack away from the radio, PC and cables. I have 5 of them and they work great, although more expensive at $100+ US each (unless on sale).

4nradio said...

This is the one I've been looking at getting:

Besides the capacity and the outputs & voltage choices, I like it's aluminum enclosure too.

Anonymous said...

I got mine today. Interesting, that I have the voltages opposite: 1A shows 5,4 V and 2,1 A shows 4,98 V!
Guy, I tested on the quietest places in the MW band and I couldn't produce any noise even when placing the unit close to Perseus. I also couldn't confirm any more noise compared from Perseus power supply, but that is another story.
What I noticed though, that the never Perseus, which has the USB cable without chokes and is on as a server, produces clearly noise to my client Perseus, when someone is tuning. I switched the cables vice versa and that helped a lot.

73, Mauno

4nradio said...

Thanks for your comments, Mauno. It's really good to hear that you didn't find any noise issues.

73, Guy

Bjarne Mjelde said...

Very good on the noise issue. I mean...that there is none ;-) When OJ arrives next weekend we'll run a laptop on its battery and a Perseus on the battery pack and do a very thorough noise investigation in the house.

Bjarne Mjelde said...

Mauno: My bad. Your observation that the 2.1A output was closest to 5V is correct, and I have updated the post accordingly.

Apple Accessories said...

It''s quite impressive.

4nradio said...

Here's the one I finally ended up buying yesterday:

The price at $31.99 USD is very good so I've bought two of them. Capacity is rated 12000 mAh. Besides the two 5V USB outputs there are 2-amp 9V and 12V outputs also.

Hopefully they are electrically quiet like your battery pack is.

73, Guy