It is getting to be more and more difficult to procure reasonably priced analogue external plug-in power supplies because just like old light bulbs they are no longer allowed to be produced due to power consumption restrictions. We are spending a lot of time to find and buy remaining stock so that we can offer our customers noise-free external power supplies. But for years, there has been an alternative.
Our MegaLoop ML200, ML052, the MegActiv MA305 as well as the GigActiv GA3005 can be operated internally with as little as 5V and so can be powered by the supplied CPI1000DP / CPI3000DP bias tee via a USB cable. In light of the annoying switching power supplies, PowerLAN and heightened mobility of listeners, this is a very practical alternative and offers much more flexibility for the customer. Unfortunately, this fact is not well known and that is why I would like to shed some light on this subject.
Here you can see an example of how you can operate the MegaLoop ML200 or the ML052 with a power bank totally independently for a couple of days. The antennas only consume max. 40mAh and can get by with a 2100mAh power bank for a few days without any problems. The power bank shown here is actually meant to recharge Smartphones. But we can use it differently as well. On the „Düsseldorf Boat Show”, I was given this power bank together with an ICOM M25 radio and attached a ML052 to it. Result: The antenna has been running on a 40m RG58 coaxial cable for four days without recharging. This also shows that the length of the cable is of no real importance.
Of course, you can use a different power bank or operate the antenna with an analogue 12V power supply, but especially when you are on the move or want to listen to your radio in a noise-free environment, a power bank is a great alternative. I have already tested some models and can offer you a suitable power bank in the Hamradioshop.
Noise-producing USB is the bane of many listeners. . Our bias tees (CPI1000DP or CPI3000DP) have special sieve filters built in to avoid such interferences. Here I show you the effect on the noise floor:
Active antenna: GigActiv 3005 0n 147.00 kHz
1) Power supply of the antenna via a 12V analogue power supply with transformer:
Please note the noise level (-126dB), the SNR and the level at 147 kHz (-116dB). Everything is looking fine.
2) Here is the spectrum with the GigActiv antenna being powered via the USB connector of the netbook:
As you can see, the noise floor and the level was re4duced by 7 dB. But the SNR has risen by 5dB! The amplitude of the station at 153 kHz has improved considerably and has more modulation which had been drowned out before.
3) And finally, the antenna is powered by a USB-power bank:
The noise floor has been reduced by a further 1-2dB and the SNR has improved by 1-2dB
- In no instance is the power supply by USB worse than the “normal” supply unit. It’s rather better and more flexible.
- This makes portable operation a lot easier and causes less internal noise.
- The difference between what is shown in picture no. 1 and no. 2 is not necessarily so great. It depends on how the supply voltage is made “unclean” by, e.g., PLC etc. I have experienced this phenomenon even when travelling.
The advantages for portable operation
When travelling, you do not necessarily want to bring a big analogue power unit with you.. You want to keep your baggage as light as possible because of airline weight restrictions . It must also be mentioned that analogue power supplies have a specific power range, e.g., a 240V AC unit is of no use in the USA with its 110V AC.
I always put my active loop antenna ML200 (I use meanwhile a ML052), 5 meters (16,40 feet) of copper wire, the bias tee, a 2 and a 5 meters (16,40 feet) coaxial cable, 2 suction cups, a USB cable and a power bank in my carry-on. Because I always listen to the radio via a PC, I can power the antenna with either the Notebook or via the USB connector on the rear panel of the RadioJet 1305S. I have the power bank for recharging my Smartphone with me anyway and can use it at the same time for the antenna. At the hotel, I attach the ML200 loop antenna to a window with the suction cups. It only takes three minutes before you are “On air” and can listen to stations you would never hear at home.
Friends of the great outdoors can escape the noise of the city and listen to the radio in a noise-free environment. As already mentioned in my article “Designing a really portable SDR” this works for many hours. As can be seen in the photo, I just put the MegaLoop ML200 (active loop antenna) over the hatchback of the Caddy, so that my Megaloop was hanging freely and even gave me some shade. I was outside for 5 – 6 hours without any other power supply and would have been able to use the antenna for an additional three hours.
My hope is that with this article I could show you how well and how much to your advantage you can use the widely-available USB power supply as a power unit.