# How much power does an RTL-SDR draw?

Background: Last night (and the night before) I was playing with my RTL-SDR and GNU-Radio again. Working with my FM Receiver, (which was working previously by the way), I detected that last night I was not getting any output? No matter where I tuned, I only got noise.

This had me flummoxed! This GNU-Radio flow-graph was working not more than a couple of months ago. What changed since then? The version of GNU Radio is the same (GNU Radio Companion 3.7.11). The Dongle is the same NooElec RTL-SDR Dongle.

CubicSDR: I then, just as a sanity check, decided to compare with CubicSDR. With Cubic-SDR and the same RTL-SDR Dongle connected to the same front panel USB, I immediately got an output when tuned to the right Radio-station frequency.

Connect to Motherboard's USB: Then just to test, I turned off CubicSDR. Unplugged the RTL-SDR Dongle from the front panel of the PC and put it in one of the four USB sockets that are directly attached to the motherboard and can be reached from the backside of the PC. I restarted GNU Radio and executed the same flowgraph for the FM Radio. And this time I got an output. I could listen to some radio stations.

1. So, it seems the front panel USB sockets are maybe not providing enough power for the Dongle to work? I googled how much power the Dongle draws? and apparently it varies from model to model.

2. Does running a GNU Radio flow graph stress the Dongle more, so that it has to draw more power from the USB? Because the CubicSDR was working without a problem when the RTL-SDR Dongle was connected to the same front panel USB where GNU Radio flowgraph was not giving any output. (The flowgraph is the same as in my first question, also shown below at the end of this post).

3. I am looking to buy, then, an USB extension set, to power the RTL-SDR externally. (As I am worried, it might be drawing too much power and could possibly damage the Motherboard, as happened to this guy's phone? And also to have the Dongle running stably.)

4. On a further note, if it is indeed a power issue, then it is a tricky little pitfall that a n00b like me can fall in. Because you get no error, no warning. The flowgraph runs. Everything seems to be working, except you get no output. You can never be really sure, if your flow graph has a bug or your Dongle is not working. How (IF it is even at all possible) can one be sure that the Dongle at least, is working correctly when testing different flowgraphs, applications, etc?

To extend what hotpaw2 said:

So, it seems the front panel USB sockets are maybe not providing enough power for the Dongle to work? I googled how much power the Dongle draws? and apparently it varies from model to model.

Exactly, different models use different tuners, some additional amplifiers, and some use linear power supplies only, others mix linear and switch-mode power supplies.

The actual power draw depends on frequency, sampling rate, gain, and a few other factors.

Does running a GNU Radio flow graph stress the Dongle more, so that it has to draw more power from the USB? Because the CubicSDR was working without a problem when the RTL-SDR Dongle was connected to the same front panel USB where GNU Radio flowgraph was not giving any output. (The flowgraph is the same as in my first question, also shown below at the end of this post).

The software using the rtlsdr driver to get the same amount of data at the same gain from the same frequency shouldn't matter.

But it might very well be that e.g. you're using GNU Radio to sample at 2MS/s and Cubic for 250 kS/s, and that makes a difference.

I am looking to buy, then, an USB extension set, to power the RTL-SDR externally. (As I am worried, it might be drawing too much power and could possibly damage the Motherboard, as happened to this guy's phone? And also to have the Dongle running stably.)

I've never seen that happen. USB ports are generally protected against overcurrent, and you'll really need a lot of bad luck or malicious intent to damage one electrically.

On a further note, if it is indeed a power issue, then it is a tricky little pitfall that a n00b like me can fall in. Because you get no error, no warning. The flowgraph runs. Everything seems to be working, except you get no output. You can never be really sure, if your flow graph has a bug or your Dongle is not working. How (IF it is even at all possible) can one be sure that the Dongle at least, is working correctly when testing different flowgraphs, applications, etc?

The console output of gr-osmosdr usually contains info on that.

general remarks:

• gr-wxgui is deprecated. We've removed it, after repeating this sentence for four years, from the current version of GNU Radio. Use Qt GUI instead. It's more efficient, more stable, and we're able to fix it when it breaks.
• Ok Marcus. As always thanks for your detailed reply. (I'd upvote your answer and the other one also, but unfortunately, I've used all 40 upvotes for today.) :) – Duck Dodgers Aug 8 '19 at 16:08

I have used RTL-SDR USB peripherals from several vendors. They run at different temperatures (implying different power draws), which suggests that your question does not have a single answer. The power level also seems to vary with what the device is doing (idle, streaming, sample rate, etc.) So you probably need to measure the USB current on your particular device, perhaps using a USB power meter (commonly available from Amazon, eBay, etc.)

• The small Noolec RTL-SDR I tried ran hottest, and eventually stopped working, which I assume to be a temperature related failure. – hotpaw2 Aug 8 '19 at 14:06
• Thank you for your answer. I will check out the USB power meter. I didn't know such a thing existed. – Duck Dodgers Aug 8 '19 at 14:08