5
\$\begingroup\$

I'm building a quadcopter using Cortex A8 and I would like to use this USB WIFI dongle.

According to the description this is 3000 mW. What does this mean? 3000 mW consumption? In the USB 2.0 the maximum power can is the following 500 mA x 5V = 2500 mW. What is the 3000mW in this case? I also saw other WiFi dongle with 6000 mW powered from USB 2.0.

\$\endgroup\$
  • \$\begingroup\$ Surely the datasheet gives the power input requirements!? \$\endgroup\$ – Olin Lathrop Jul 2 '12 at 19:15
4
\$\begingroup\$

From the less than complete information provided in the advertisement, and the use of "3000 mW" on the box and on the device itself and elsewhere, it is almost certain that they are referring to the peak transmit power of the WiFi RF output stage. This is liable to be 3 Watts (= 3000 mW) DC in and not RF out, and there is a moderately good chance that actual power level is not even that high.

They say " ... The high power adapter greatly improves stability. ..." and " ... Great coverage 3000mW ... ".

It is common to market equipment wit stated power ratings that are either above actual or which relate to the power at the peak of a cycle or over a very short transmission period and which do not represent power as it would usually be measured or actual mean power over even quite short periods of time.

Peak RF power and mean RF power while transmitting and mean RF power can all be substantially different, and it is possible to have peak powers of 3W from a 2.5W DC source with the extra being provided for the very brief periods required by capacitors.


If I was building a Quad-Copter I'd want the performance of my coms link to be very well known and to be based on a reasonably complete set of relevant data. This unit cites "3000 mW" in a number of places but does not mention transmit power in the specifications and makes no mention of receiver sensitivity. About the only concessions to formal specifications are a statement of maximum VSWR and claimed antenna gain.

For this utterly indispensable part of a quad-copter system I'd buy something else which had more complete specifications and which was produced and backed by a reputable manufacturer.

One possible precaution against uncertain link performance would be a "fly back towards launch position on loss of signal" mode, with GPS, inertial and other relevant data input - but that's a whole new topic.

\$\endgroup\$
  • \$\begingroup\$ Can you suggest a WiFi module with GPS please, also I would like to transfer video from the Quadcopter, because of this it's important the bandwidth. \$\endgroup\$ – Kicsi Mano Jul 3 '12 at 14:44
  • \$\begingroup\$ If those 3000mW were real it would be illegal. And "11dB omnidirectional antenna" also triggered by bullshit detectors. \$\endgroup\$ – starblue Jul 5 '12 at 8:32
  • \$\begingroup\$ @starblue - A vaguely careful reading of my politely worded response may lead you to conclude that I tend to agree with your analysis :-). 11 dBi is not overly hard - but not so with a rubber ducky or mini version thereof as shown in the picture. A Yagi or Pringles Cantenna may be more in order, but pointing it at base from the quadcopter at all times (or at quadcopter from base) may be "problemmatic" [tm]. \$\endgroup\$ – Russell McMahon Jul 6 '12 at 3:54
  • \$\begingroup\$ @Russell McMahon Yes, but a Yagi or Pringles Cantenna isn't omnidirectional, quite far from it. It's the directionality that gives you the antenna gain, so "11dB" and "omnidirectional" contradict each other. (I'm sure you know this, but as a service to other readers I'm making it explicit.) \$\endgroup\$ – starblue Jul 6 '12 at 7:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.